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Diffstat (limited to 'compiler/Language/Haskell/Syntax/Expr.hs')
| -rw-r--r-- | compiler/Language/Haskell/Syntax/Expr.hs | 1776 |
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diff --git a/compiler/Language/Haskell/Syntax/Expr.hs b/compiler/Language/Haskell/Syntax/Expr.hs new file mode 100644 index 0000000000..ecc7c9f828 --- /dev/null +++ b/compiler/Language/Haskell/Syntax/Expr.hs @@ -0,0 +1,1776 @@ +{-# LANGUAGE CPP #-} +{-# LANGUAGE ConstraintKinds #-} +{-# LANGUAGE DataKinds #-} +{-# LANGUAGE DeriveDataTypeable #-} +{-# LANGUAGE ExistentialQuantification #-} +{-# LANGUAGE FlexibleContexts #-} +{-# LANGUAGE FlexibleInstances #-} +{-# LANGUAGE LambdaCase #-} +{-# LANGUAGE ScopedTypeVariables #-} +{-# LANGUAGE StandaloneDeriving #-} +{-# LANGUAGE TypeApplications #-} +{-# LANGUAGE TypeFamilyDependencies #-} +{-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow] + -- in module Language.Haskell.Syntax.Extension + +{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-} + +{- +(c) The University of Glasgow 2006 +(c) The GRASP/AQUA Project, Glasgow University, 1992-1998 +-} + +-- See Note [Language.Haskell.Syntax.* Hierarchy] for why not GHC.Hs.* + +-- | Abstract Haskell syntax for expressions. +module Language.Haskell.Syntax.Expr where + +#include "HsVersions.h" + +-- friends: +import GHC.Prelude + +import Language.Haskell.Syntax.Decls +import Language.Haskell.Syntax.Pat +import Language.Haskell.Syntax.Lit +import Language.Haskell.Syntax.Extension +import Language.Haskell.Syntax.Type +import Language.Haskell.Syntax.Binds + +-- others: +import GHC.Tc.Types.Evidence +import GHC.Core +import GHC.Types.Name +import GHC.Types.Basic +import GHC.Types.Fixity +import GHC.Types.SourceText +import GHC.Types.SrcLoc +import GHC.Core.ConLike +import GHC.Unit.Module (ModuleName) +import GHC.Utils.Outputable +import GHC.Utils.Panic +import GHC.Data.FastString +import GHC.Core.Type + +-- libraries: +import Data.Data hiding (Fixity(..)) +import qualified Data.Data as Data (Fixity(..)) + +import GHCi.RemoteTypes ( ForeignRef ) +import qualified Language.Haskell.TH as TH (Q) + +{- +************************************************************************ +* * +\subsection{Expressions proper} +* * +************************************************************************ +-} + +-- * Expressions proper + +-- | Located Haskell Expression +type LHsExpr p = XRec p (HsExpr p) + -- ^ May have 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnComma' when + -- in a list + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + +------------------------- +{- Note [NoSyntaxExpr] +~~~~~~~~~~~~~~~~~~~~~~ +Syntax expressions can be missing (NoSyntaxExprRn or NoSyntaxExprTc) +for several reasons: + + 1. As described in Note [Rebindable if] + + 2. In order to suppress "not in scope: xyz" messages when a bit of + rebindable syntax does not apply. For example, when using an irrefutable + pattern in a BindStmt, we don't need a `fail` operator. + + 3. Rebindable syntax might just not make sense. For example, a BodyStmt + contains the syntax for `guard`, but that's used only in monad comprehensions. + If we had more of a whiz-bang type system, we might be able to rule this + case out statically. +-} + +-- | Syntax Expression +-- +-- SyntaxExpr is represents the function used in interpreting rebindable +-- syntax. In the parser, we have no information to supply; in the renamer, +-- we have the name of the function (but see +-- Note [Monad fail : Rebindable syntax, overloaded strings] for a wrinkle) +-- and in the type-checker we have a more elaborate structure 'SyntaxExprTc'. +-- +-- In some contexts, rebindable syntax is not implemented, and so we have +-- constructors to represent that possibility in both the renamer and +-- typechecker instantiations. +-- +-- E.g. @(>>=)@ is filled in before the renamer by the appropriate 'Name' for +-- @(>>=)@, and then instantiated by the type checker with its type args +-- etc +type family SyntaxExpr p + +-- | Command Syntax Table (for Arrow syntax) +type CmdSyntaxTable p = [(Name, HsExpr p)] +-- See Note [CmdSyntaxTable] + +{- +Note [CmdSyntaxTable] +~~~~~~~~~~~~~~~~~~~~~ +Used only for arrow-syntax stuff (HsCmdTop), the CmdSyntaxTable keeps +track of the methods needed for a Cmd. + +* Before the renamer, this list is an empty list + +* After the renamer, it takes the form @[(std_name, HsVar actual_name)]@ + For example, for the 'arr' method + * normal case: (GHC.Control.Arrow.arr, HsVar GHC.Control.Arrow.arr) + * with rebindable syntax: (GHC.Control.Arrow.arr, arr_22) + where @arr_22@ is whatever 'arr' is in scope + +* After the type checker, it takes the form [(std_name, <expression>)] + where <expression> is the evidence for the method. This evidence is + instantiated with the class, but is still polymorphic in everything + else. For example, in the case of 'arr', the evidence has type + forall b c. (b->c) -> a b c + where 'a' is the ambient type of the arrow. This polymorphism is + important because the desugarer uses the same evidence at multiple + different types. + +This is Less Cool than what we normally do for rebindable syntax, which is to +make fully-instantiated piece of evidence at every use site. The Cmd way +is Less Cool because + * The renamer has to predict which methods are needed. + See the tedious GHC.Rename.Expr.methodNamesCmd. + + * The desugarer has to know the polymorphic type of the instantiated + method. This is checked by Inst.tcSyntaxName, but is less flexible + than the rest of rebindable syntax, where the type is less + pre-ordained. (And this flexibility is useful; for example we can + typecheck do-notation with (>>=) :: m1 a -> (a -> m2 b) -> m2 b.) +-} + +-- | A Haskell expression. +data HsExpr p + = HsVar (XVar p) + (LIdP p) -- ^ Variable + -- See Note [Located RdrNames] + + | HsUnboundVar (XUnboundVar p) + OccName -- ^ Unbound variable; also used for "holes" + -- (_ or _x). + -- Turned from HsVar to HsUnboundVar by the + -- renamer, when it finds an out-of-scope + -- variable or hole. + -- The (XUnboundVar p) field becomes an HoleExprRef + -- after typechecking; this is where the + -- erroring expression will be written after + -- solving. See Note [Holes] in GHC.Tc.Types.Constraint. + + | HsConLikeOut (XConLikeOut p) + ConLike -- ^ After typechecker only; must be different + -- HsVar for pretty printing + + | HsRecFld (XRecFld p) + (AmbiguousFieldOcc p) -- ^ Variable pointing to record selector + -- The parser produces HsVars + -- The renamer renames record-field selectors to HsRecFld + -- The typechecker preserves HsRecFld + + | HsOverLabel (XOverLabel p) + (Maybe (IdP p)) FastString + -- ^ Overloaded label (Note [Overloaded labels] in GHC.OverloadedLabels) + -- @Just id@ means @RebindableSyntax@ is in use, and gives the id of the + -- in-scope 'fromLabel'. + -- NB: Not in use after typechecking + + | HsIPVar (XIPVar p) + HsIPName -- ^ Implicit parameter (not in use after typechecking) + | HsOverLit (XOverLitE p) + (HsOverLit p) -- ^ Overloaded literals + + | HsLit (XLitE p) + (HsLit p) -- ^ Simple (non-overloaded) literals + + | HsLam (XLam p) + (MatchGroup p (LHsExpr p)) + -- ^ Lambda abstraction. Currently always a single match + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLam', + -- 'GHC.Parser.Annotation.AnnRarrow', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsLamCase (XLamCase p) (MatchGroup p (LHsExpr p)) -- ^ Lambda-case + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLam', + -- 'GHC.Parser.Annotation.AnnCase','GHC.Parser.Annotation.AnnOpen', + -- 'GHC.Parser.Annotation.AnnClose' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsApp (XApp p) (LHsExpr p) (LHsExpr p) -- ^ Application + + | HsAppType (XAppTypeE p) -- After typechecking: the type argument + (LHsExpr p) + (LHsWcType (NoGhcTc p)) -- ^ Visible type application + -- + -- Explicit type argument; e.g f @Int x y + -- NB: Has wildcards, but no implicit quantification + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnAt', + + -- | Operator applications: + -- NB Bracketed ops such as (+) come out as Vars. + + -- NB We need an expr for the operator in an OpApp/Section since + -- the typechecker may need to apply the operator to a few types. + + | OpApp (XOpApp p) + (LHsExpr p) -- left operand + (LHsExpr p) -- operator + (LHsExpr p) -- right operand + + -- | Negation operator. Contains the negated expression and the name + -- of 'negate' + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnMinus' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | NegApp (XNegApp p) + (LHsExpr p) + (SyntaxExpr p) + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'('@, + -- 'GHC.Parser.Annotation.AnnClose' @')'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsPar (XPar p) + (LHsExpr p) -- ^ Parenthesised expr; see Note [Parens in HsSyn] + + | SectionL (XSectionL p) + (LHsExpr p) -- operand; see Note [Sections in HsSyn] + (LHsExpr p) -- operator + | SectionR (XSectionR p) + (LHsExpr p) -- operator; see Note [Sections in HsSyn] + (LHsExpr p) -- operand + + -- | Used for explicit tuples and sections thereof + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen', + -- 'GHC.Parser.Annotation.AnnClose' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + -- Note [ExplicitTuple] + | ExplicitTuple + (XExplicitTuple p) + [LHsTupArg p] + Boxity + + -- | Used for unboxed sum types + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'(#'@, + -- 'GHC.Parser.Annotation.AnnVbar', 'GHC.Parser.Annotation.AnnClose' @'#)'@, + -- + -- There will be multiple 'GHC.Parser.Annotation.AnnVbar', (1 - alternative) before + -- the expression, (arity - alternative) after it + | ExplicitSum + (XExplicitSum p) + ConTag -- Alternative (one-based) + Arity -- Sum arity + (LHsExpr p) + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnCase', + -- 'GHC.Parser.Annotation.AnnOf','GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnClose' @'}'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsCase (XCase p) + (LHsExpr p) + (MatchGroup p (LHsExpr p)) + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnIf', + -- 'GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnThen','GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnElse', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsIf (XIf p) -- GhcPs: this is a Bool; False <=> do not use + -- rebindable syntax + (LHsExpr p) -- predicate + (LHsExpr p) -- then part + (LHsExpr p) -- else part + + -- | Multi-way if + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnIf' + -- 'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnClose', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsMultiIf (XMultiIf p) [LGRHS p (LHsExpr p)] + + -- | let(rec) + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLet', + -- 'GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnClose' @'}'@,'GHC.Parser.Annotation.AnnIn' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsLet (XLet p) + (LHsLocalBinds p) + (LHsExpr p) + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDo', + -- 'GHC.Parser.Annotation.AnnOpen', 'GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnVbar', + -- 'GHC.Parser.Annotation.AnnClose' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsDo (XDo p) -- Type of the whole expression + (HsStmtContext (HsDoRn p)) + -- The parameterisation of the above is unimportant + -- because in this context we never use + -- the PatGuard or ParStmt variant + (XRec p [ExprLStmt p]) -- "do":one or more stmts + + -- | Syntactic list: [a,b,c,...] + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'['@, + -- 'GHC.Parser.Annotation.AnnClose' @']'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + -- See Note [Empty lists] + | ExplicitList + (XExplicitList p) -- Gives type of components of list + (Maybe (SyntaxExpr p)) + -- For OverloadedLists, the fromListN witness + [LHsExpr p] + + -- | Record construction + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnDotdot','GHC.Parser.Annotation.AnnClose' @'}'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | RecordCon + { rcon_ext :: XRecordCon p + , rcon_con_name :: LIdP p -- The constructor name; + -- not used after type checking + , rcon_flds :: HsRecordBinds p } -- The fields + + -- | Record update + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnDotdot','GHC.Parser.Annotation.AnnClose' @'}'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | RecordUpd + { rupd_ext :: XRecordUpd p + , rupd_expr :: LHsExpr p + , rupd_flds :: [LHsRecUpdField p] + } + -- For a type family, the arg types are of the *instance* tycon, + -- not the family tycon + + -- | Expression with an explicit type signature. @e :: type@ + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDcolon' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | ExprWithTySig + (XExprWithTySig p) + + (LHsExpr p) + (LHsSigWcType (NoGhcTc p)) + + -- | Arithmetic sequence + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'['@, + -- 'GHC.Parser.Annotation.AnnComma','GHC.Parser.Annotation.AnnDotdot', + -- 'GHC.Parser.Annotation.AnnClose' @']'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | ArithSeq + (XArithSeq p) + (Maybe (SyntaxExpr p)) + -- For OverloadedLists, the fromList witness + (ArithSeqInfo p) + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + ----------------------------------------------------------- + -- MetaHaskell Extensions + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen', + -- 'GHC.Parser.Annotation.AnnOpenE','GHC.Parser.Annotation.AnnOpenEQ', + -- 'GHC.Parser.Annotation.AnnClose','GHC.Parser.Annotation.AnnCloseQ' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsBracket (XBracket p) (HsBracket p) + + -- See Note [Pending Splices] + | HsRnBracketOut + (XRnBracketOut p) + (HsBracket (HsBracketRn p)) -- Output of the renamer is the *original* renamed + -- expression, plus + [PendingRnSplice' p] -- _renamed_ splices to be type checked + + | HsTcBracketOut + (XTcBracketOut p) + (Maybe QuoteWrapper) -- The wrapper to apply type and dictionary argument + -- to the quote. + (HsBracket (HsBracketRn p)) -- Output of the type checker is the *original* + -- renamed expression, plus + [PendingTcSplice' p] -- _typechecked_ splices to be + -- pasted back in by the desugarer + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen', + -- 'GHC.Parser.Annotation.AnnClose' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsSpliceE (XSpliceE p) (HsSplice p) + + ----------------------------------------------------------- + -- Arrow notation extension + + -- | @proc@ notation for Arrows + -- + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnProc', + -- 'GHC.Parser.Annotation.AnnRarrow' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsProc (XProc p) + (LPat p) -- arrow abstraction, proc + (LHsCmdTop p) -- body of the abstraction + -- always has an empty stack + + --------------------------------------- + -- static pointers extension + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnStatic', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsStatic (XStatic p) -- Free variables of the body + (LHsExpr p) -- Body + + --------------------------------------- + -- Haskell program coverage (Hpc) Support + + | HsTick + (XTick p) + (Tickish (IdP p)) + (LHsExpr p) -- sub-expression + + | HsBinTick + (XBinTick p) + Int -- module-local tick number for True + Int -- module-local tick number for False + (LHsExpr p) -- sub-expression + + --------------------------------------- + -- Expressions annotated with pragmas, written as {-# ... #-} + | HsPragE (XPragE p) (HsPragE p) (LHsExpr p) + + | XExpr !(XXExpr p) + -- Note [Trees that Grow] extension constructor for the + -- general idea, and Note [Rebindable syntax and HsExpansion] + -- for an example of how we use it. + +-- | The AST used to hard-refer to GhcPass, which was a layer violation. For now, +-- we paper it over with this new extension point. +type family HsDoRn p +type family HsBracketRn p +type family PendingRnSplice' p +type family PendingTcSplice' p + +-- --------------------------------------------------------------------- + +{- +Note [Rebindable syntax and HsExpansion] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +We implement rebindable syntax (RS) support by performing a desugaring +in the renamer. We transform GhcPs expressions affected by RS into the +appropriate desugared form, but **annotated with the original expression**. + +Let us consider a piece of code like: + + {-# LANGUAGE RebindableSyntax #-} + ifThenElse :: Char -> () -> () -> () + ifThenElse _ _ _ = () + x = if 'a' then () else True + +The parsed AST for the RHS of x would look something like (slightly simplified): + + L locif (HsIf (L loca 'a') (L loctrue ()) (L locfalse True)) + +Upon seeing such an AST with RS on, we could transform it into a +mere function call, as per the RS rules, equivalent to the +following function application: + + ifThenElse 'a' () True + +which doesn't typecheck. But GHC would report an error about +not being able to match the third argument's type (Bool) with the +expected type: (), in the expression _as desugared_, i.e in +the aforementioned function application. But the user never +wrote a function application! This would be pretty bad. + +To remedy this, instead of transforming the original HsIf +node into mere applications of 'ifThenElse', we keep the +original 'if' expression around too, using the TTG +XExpr extension point to allow GHC to construct an +'HsExpansion' value that will keep track of the original +expression in its first field, and the desugared one in the +second field. The resulting renamed AST would look like: + + L locif (XExpr + (HsExpanded + (HsIf (L loca 'a') + (L loctrue ()) + (L locfalse True) + ) + (App (L generatedSrcSpan + (App (L generatedSrcSpan + (App (L generatedSrcSpan (Var ifThenElse)) + (L loca 'a') + ) + ) + (L loctrue ()) + ) + ) + (L locfalse True) + ) + ) + ) + +When comes the time to typecheck the program, we end up calling +tcMonoExpr on the AST above. If this expression gives rise to +a type error, then it will appear in a context line and GHC +will pretty-print it using the 'Outputable (HsExpansion a b)' +instance defined below, which *only prints the original +expression*. This is the gist of the idea, but is not quite +enough to recover the error messages that we had with the +SyntaxExpr-based, typechecking/desugaring-to-core time +implementation of rebindable syntax. The key idea is to decorate +some elements of the desugared expression so as to be able to +give them a special treatment when typechecking the desugared +expression, to print a different context line or skip one +altogether. + +Whenever we 'setSrcSpan' a 'generatedSrcSpan', we update a field in +TcLclEnv called 'tcl_in_gen_code', setting it to True, which indicates that we +entered generated code, i.e code fabricated by the compiler when rebinding some +syntax. If someone tries to push some error context line while that field is set +to True, the pushing won't actually happen and the context line is just dropped. +Once we 'setSrcSpan' a real span (for an expression that was in the original +source code), we set 'tcl_in_gen_code' back to False, indicating that we +"emerged from the generated code tunnel", and that the expressions we will be +processing are relevant to report in context lines again. + +You might wonder why we store a RealSrcSpan in addition to a Bool in +the TcLclEnv: could we not store a Maybe RealSrcSpan? The problem is +that we still generate constraints when processing generated code, +and a CtLoc must contain a RealSrcSpan -- otherwise, error messages +might appear without source locations. So we keep the RealSrcSpan of +the last location spotted that wasn't generated; it's as good as +we're going to get in generated code. Once we get to sub-trees that +are not generated, then we update the RealSrcSpan appropriately, and +set the tcl_in_gen_code Bool to False. + +--- + +A general recipe to follow this approach for new constructs could go as follows: + +- Remove any GhcRn-time SyntaxExpr extensions to the relevant constructor for your + construct, in HsExpr or related syntax data types. +- At renaming-time: + - take your original node of interest (HsIf above) + - rename its subexpressions (condition, true branch, false branch above) + - construct the suitable "rebound"-and-renamed result (ifThenElse call + above), where the 'SrcSpan' attached to any _fabricated node_ (the + HsVar/HsApp nodes, above) is set to 'generatedSrcSpan' + - take both the original node and that rebound-and-renamed result and wrap + them in an XExpr: XExpr (HsExpanded <original node> <desugared>) + - At typechecking-time: + - remove any logic that was previously dealing with your rebindable + construct, typically involving [tc]SyntaxOp, SyntaxExpr and friends. + - the XExpr (HsExpanded ... ...) case in tcExpr already makes sure that we + typecheck the desugared expression while reporting the original one in + errors + +-} + +-- See Note [Rebindable syntax and HsExpansion] just above. +data HsExpansion a b + = HsExpanded a b + deriving Data + +-- | Build a "wrapped" 'HsExpansion' out of an extension constructor, +-- and the two components of the expansion: original and desugared +-- expressions. +-- +-- See Note [Rebindable Syntax and HsExpansion] above for more details. +mkExpanded + :: (HsExpansion a b -> b) -- ^ XExpr, XCmd, ... + -> a -- ^ source expression ('GhcPs') + -> b -- ^ "desugared" expression + -- ('GhcRn') + -> b -- ^ suitably wrapped + -- 'HsExpansion' +mkExpanded xwrap a b = xwrap (HsExpanded a b) + +-- | Just print the original expression (the @a@). +instance (Outputable a, Outputable b) => Outputable (HsExpansion a b) where + ppr (HsExpanded a b) = ifPprDebug (vcat [ppr a, ppr b]) (ppr a) + +-- --------------------------------------------------------------------- + +-- | A pragma, written as {-# ... #-}, that may appear within an expression. +data HsPragE p + = HsPragSCC (XSCC p) + SourceText -- Note [Pragma source text] in GHC.Types.SourceText + StringLiteral -- "set cost centre" SCC pragma + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen', + -- 'GHC.Parser.Annotation.AnnOpen' @'{-\# GENERATED'@, + -- 'GHC.Parser.Annotation.AnnVal','GHC.Parser.Annotation.AnnVal', + -- 'GHC.Parser.Annotation.AnnColon','GHC.Parser.Annotation.AnnVal', + -- 'GHC.Parser.Annotation.AnnMinus', + -- 'GHC.Parser.Annotation.AnnVal','GHC.Parser.Annotation.AnnColon', + -- 'GHC.Parser.Annotation.AnnVal', + -- 'GHC.Parser.Annotation.AnnClose' @'\#-}'@ + + | XHsPragE !(XXPragE p) + +-- | Located Haskell Tuple Argument +-- +-- 'HsTupArg' is used for tuple sections +-- @(,a,)@ is represented by +-- @ExplicitTuple [Missing ty1, Present a, Missing ty3]@ +-- Which in turn stands for @(\x:ty1 \y:ty2. (x,a,y))@ +type LHsTupArg id = XRec id (HsTupArg id) +-- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnComma' + +-- For details on above see note [Api annotations] in GHC.Parser.Annotation + +-- | Haskell Tuple Argument +data HsTupArg id + = Present (XPresent id) (LHsExpr id) -- ^ The argument + | Missing (XMissing id) -- ^ The argument is missing, but this is its type + | XTupArg !(XXTupArg id) -- ^ Note [Trees that Grow] extension point + +{- +Note [Parens in HsSyn] +~~~~~~~~~~~~~~~~~~~~~~ +HsPar (and ParPat in patterns, HsParTy in types) is used as follows + + * HsPar is required; the pretty printer does not add parens. + + * HsPars are respected when rearranging operator fixities. + So a * (b + c) means what it says (where the parens are an HsPar) + + * For ParPat and HsParTy the pretty printer does add parens but this should be + a no-op for ParsedSource, based on the pretty printer round trip feature + introduced in + https://phabricator.haskell.org/rGHC499e43824bda967546ebf95ee33ec1f84a114a7c + + * ParPat and HsParTy are pretty printed as '( .. )' regardless of whether or + not they are strictly necessary. This should be addressed when #13238 is + completed, to be treated the same as HsPar. + + +Note [Sections in HsSyn] +~~~~~~~~~~~~~~~~~~~~~~~~ +Sections should always appear wrapped in an HsPar, thus + HsPar (SectionR ...) +The parser parses sections in a wider variety of situations +(See Note [Parsing sections]), but the renamer checks for those +parens. This invariant makes pretty-printing easier; we don't need +a special case for adding the parens round sections. + +Note [Rebindable if] +~~~~~~~~~~~~~~~~~~~~ +The rebindable syntax for 'if' is a bit special, because when +rebindable syntax is *off* we do not want to treat + (if c then t else e) +as if it was an application (ifThenElse c t e). Why not? +Because we allow an 'if' to return *unboxed* results, thus + if blah then 3# else 4# +whereas that would not be possible using a all to a polymorphic function +(because you can't call a polymorphic function at an unboxed type). + +So we use NoSyntaxExpr to mean "use the old built-in typing rule". + +A further complication is that, in the `deriving` code, we never want +to use rebindable syntax. So, even in GhcPs, we want to denote whether +to use rebindable syntax or not. This is done via the type instance +for XIf GhcPs. + +Note [Record Update HsWrapper] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +There is a wrapper in RecordUpd which is used for the *required* +constraints for pattern synonyms. This wrapper is created in the +typechecking and is then directly used in the desugaring without +modification. + +For example, if we have the record pattern synonym P, + pattern P :: (Show a) => a -> Maybe a + pattern P{x} = Just x + + foo = (Just True) { x = False } +then `foo` desugars to something like + foo = case Just True of + P x -> P False +hence we need to provide the correct dictionaries to P's matcher on +the RHS so that we can build the expression. + +Note [Located RdrNames] +~~~~~~~~~~~~~~~~~~~~~~~ +A number of syntax elements have seemingly redundant locations attached to them. +This is deliberate, to allow transformations making use of the API Annotations +to easily correlate a Located Name in the RenamedSource with a Located RdrName +in the ParsedSource. + +There are unfortunately enough differences between the ParsedSource and the +RenamedSource that the API Annotations cannot be used directly with +RenamedSource, so this allows a simple mapping to be used based on the location. + +Note [ExplicitTuple] +~~~~~~~~~~~~~~~~~~~~ +An ExplicitTuple is never just a data constructor like (,,,). +That is, the `[LHsTupArg p]` argument of `ExplicitTuple` has at least +one `Present` member (and is thus never empty). + +A tuple data constructor like () or (,,,) is parsed as an `HsVar`, not an +`ExplicitTuple`, and stays that way. This is important for two reasons: + + 1. We don't need -XTupleSections for (,,,) + 2. The type variables in (,,,) can be instantiated with visible type application. + That is, + + (,,) :: forall a b c. a -> b -> c -> (a,b,c) + (True,,) :: forall {b} {c}. b -> c -> (Bool,b,c) + + Note that the tuple section has *inferred* arguments, while the data + constructor has *specified* ones. + (See Note [Required, Specified, and Inferred for types] in GHC.Tc.TyCl + for background.) + +Sadly, the grammar for this is actually ambiguous, and it's only thanks to the +preference of a shift in a shift/reduce conflict that the parser works as this +Note details. Search for a reference to this Note in GHC.Parser for further +explanation. + +Note [Empty lists] +~~~~~~~~~~~~~~~~~~ +An empty list could be considered either a data constructor (stored with +HsVar) or an ExplicitList. This Note describes how empty lists flow through the +various phases and why. + +Parsing +------- +An empty list is parsed by the sysdcon nonterminal. It thus comes to life via +HsVar nilDataCon (defined in GHC.Builtin.Types). A freshly-parsed (HsExpr GhcPs) empty list +is never a ExplicitList. + +Renaming +-------- +If -XOverloadedLists is enabled, we must type-check the empty list as if it +were a call to fromListN. (This is true regardless of the setting of +-XRebindableSyntax.) This is very easy if the empty list is an ExplicitList, +but an annoying special case if it's an HsVar. So the renamer changes a +HsVar nilDataCon to an ExplicitList [], but only if -XOverloadedLists is on. +(Why not always? Read on, dear friend.) This happens in the HsVar case of rnExpr. + +Type-checking +------------- +We want to accept an expression like [] @Int. To do this, we must infer that +[] :: forall a. [a]. This is easy if [] is a HsVar with the right DataCon inside. +However, the type-checking for explicit lists works differently: [x,y,z] is never +polymorphic. Instead, we unify the types of x, y, and z together, and use the +unified type as the argument to the cons and nil constructors. Thus, treating +[] as an empty ExplicitList in the type-checker would prevent [] @Int from working. + +However, if -XOverloadedLists is on, then [] @Int really shouldn't be allowed: +it's just like fromListN 0 [] @Int. Since + fromListN :: forall list. IsList list => Int -> [Item list] -> list +that expression really should be rejected. Thus, the renamer's behaviour is +exactly what we want: treat [] as a datacon when -XNoOverloadedLists, and as +an empty ExplicitList when -XOverloadedLists. + +See also #13680, which requested [] @Int to work. +-} + + +----------------------- +pprExternalSrcLoc :: (StringLiteral,(Int,Int),(Int,Int)) -> SDoc +pprExternalSrcLoc (StringLiteral _ src,(n1,n2),(n3,n4)) + = ppr (src,(n1,n2),(n3,n4)) + +{- +HsSyn records exactly where the user put parens, with HsPar. +So generally speaking we print without adding any parens. +However, some code is internally generated, and in some places +parens are absolutely required; so for these places we use +pprParendLExpr (but don't print double parens of course). + +For operator applications we don't add parens, because the operator +fixities should do the job, except in debug mode (-dppr-debug) so we +can see the structure of the parse tree. +-} + +{- +************************************************************************ +* * +\subsection{Commands (in arrow abstractions)} +* * +************************************************************************ + +We re-use HsExpr to represent these. +-} + +-- | Located Haskell Command (for arrow syntax) +type LHsCmd id = XRec id (HsCmd id) + +-- | Haskell Command (e.g. a "statement" in an Arrow proc block) +data HsCmd id + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.Annlarrowtail', + -- 'GHC.Parser.Annotation.Annrarrowtail','GHC.Parser.Annotation.AnnLarrowtail', + -- 'GHC.Parser.Annotation.AnnRarrowtail' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + = HsCmdArrApp -- Arrow tail, or arrow application (f -< arg) + (XCmdArrApp id) -- type of the arrow expressions f, + -- of the form a t t', where arg :: t + (LHsExpr id) -- arrow expression, f + (LHsExpr id) -- input expression, arg + HsArrAppType -- higher-order (-<<) or first-order (-<) + Bool -- True => right-to-left (f -< arg) + -- False => left-to-right (arg >- f) + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpenB' @'(|'@, + -- 'GHC.Parser.Annotation.AnnCloseB' @'|)'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | HsCmdArrForm -- Command formation, (| e cmd1 .. cmdn |) + (XCmdArrForm id) + (LHsExpr id) -- The operator. + -- After type-checking, a type abstraction to be + -- applied to the type of the local environment tuple + LexicalFixity -- Whether the operator appeared prefix or infix when + -- parsed. + (Maybe Fixity) -- fixity (filled in by the renamer), for forms that + -- were converted from OpApp's by the renamer + [LHsCmdTop id] -- argument commands + + | HsCmdApp (XCmdApp id) + (LHsCmd id) + (LHsExpr id) + + | HsCmdLam (XCmdLam id) + (MatchGroup id (LHsCmd id)) -- kappa + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLam', + -- 'GHC.Parser.Annotation.AnnRarrow', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdPar (XCmdPar id) + (LHsCmd id) -- parenthesised command + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnOpen' @'('@, + -- 'GHC.Parser.Annotation.AnnClose' @')'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdCase (XCmdCase id) + (LHsExpr id) + (MatchGroup id (LHsCmd id)) -- bodies are HsCmd's + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnCase', + -- 'GHC.Parser.Annotation.AnnOf','GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnClose' @'}'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdLamCase (XCmdLamCase id) + (MatchGroup id (LHsCmd id)) -- bodies are HsCmd's + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLam', + -- 'GHC.Parser.Annotation.AnnCase','GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnClose' @'}'@ + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdIf (XCmdIf id) + (SyntaxExpr id) -- cond function + (LHsExpr id) -- predicate + (LHsCmd id) -- then part + (LHsCmd id) -- else part + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnIf', + -- 'GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnThen','GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnElse', + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdLet (XCmdLet id) + (LHsLocalBinds id) -- let(rec) + (LHsCmd id) + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLet', + -- 'GHC.Parser.Annotation.AnnOpen' @'{'@, + -- 'GHC.Parser.Annotation.AnnClose' @'}'@,'GHC.Parser.Annotation.AnnIn' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | HsCmdDo (XCmdDo id) -- Type of the whole expression + (XRec id [CmdLStmt id]) + -- ^ - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnDo', + -- 'GHC.Parser.Annotation.AnnOpen', 'GHC.Parser.Annotation.AnnSemi', + -- 'GHC.Parser.Annotation.AnnVbar', + -- 'GHC.Parser.Annotation.AnnClose' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + + | XCmd !(XXCmd id) -- Note [Trees that Grow] extension point + + +-- | Haskell Array Application Type +data HsArrAppType = HsHigherOrderApp | HsFirstOrderApp + deriving Data + + +{- | Top-level command, introducing a new arrow. +This may occur inside a proc (where the stack is empty) or as an +argument of a command-forming operator. +-} + +-- | Located Haskell Top-level Command +type LHsCmdTop p = XRec p (HsCmdTop p) + +-- | Haskell Top-level Command +data HsCmdTop p + = HsCmdTop (XCmdTop p) + (LHsCmd p) + | XCmdTop !(XXCmdTop p) -- Note [Trees that Grow] extension point + +----------------------- + +{- +************************************************************************ +* * +\subsection{Record binds} +* * +************************************************************************ +-} + +-- | Haskell Record Bindings +type HsRecordBinds p = HsRecFields p (LHsExpr p) + +{- +************************************************************************ +* * +\subsection{@Match@, @GRHSs@, and @GRHS@ datatypes} +* * +************************************************************************ + +@Match@es are sets of pattern bindings and right hand sides for +functions, patterns or case branches. For example, if a function @g@ +is defined as: +\begin{verbatim} +g (x,y) = y +g ((x:ys),y) = y+1, +\end{verbatim} +then \tr{g} has two @Match@es: @(x,y) = y@ and @((x:ys),y) = y+1@. + +It is always the case that each element of an @[Match]@ list has the +same number of @pats@s inside it. This corresponds to saying that +a function defined by pattern matching must have the same number of +patterns in each equation. +-} + +data MatchGroup p body + = MG { mg_ext :: XMG p body -- Post-typechecker, types of args and result + , mg_alts :: XRec p [LMatch p body] -- The alternatives + , mg_origin :: Origin } + -- The type is the type of the entire group + -- t1 -> ... -> tn -> tr + -- where there are n patterns + | XMatchGroup !(XXMatchGroup p body) + +data MatchGroupTc + = MatchGroupTc + { mg_arg_tys :: [Scaled Type] -- Types of the arguments, t1..tn + , mg_res_ty :: Type -- Type of the result, tr + } deriving Data + +-- | Located Match +type LMatch id body = XRec id (Match id body) +-- ^ May have 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnSemi' when in a +-- list + +-- For details on above see note [Api annotations] in GHC.Parser.Annotation +data Match p body + = Match { + m_ext :: XCMatch p body, + m_ctxt :: HsMatchContext (NoGhcTc p), + -- See note [m_ctxt in Match] + m_pats :: [LPat p], -- The patterns + m_grhss :: (GRHSs p body) + } + | XMatch !(XXMatch p body) + +{- +Note [m_ctxt in Match] +~~~~~~~~~~~~~~~~~~~~~~ + +A Match can occur in a number of contexts, such as a FunBind, HsCase, HsLam and +so on. + +In order to simplify tooling processing and pretty print output, the provenance +is captured in an HsMatchContext. + +This is particularly important for the API Annotations for a multi-equation +FunBind. + +The parser initially creates a FunBind with a single Match in it for +every function definition it sees. + +These are then grouped together by getMonoBind into a single FunBind, +where all the Matches are combined. + +In the process, all the original FunBind fun_id's bar one are +discarded, including the locations. + +This causes a problem for source to source conversions via API +Annotations, so the original fun_ids and infix flags are preserved in +the Match, when it originates from a FunBind. + +Example infix function definition requiring individual API Annotations + + (&&& ) [] [] = [] + xs &&& [] = xs + ( &&& ) [] ys = ys + + + +-} + + +isInfixMatch :: Match id body -> Bool +isInfixMatch match = case m_ctxt match of + FunRhs {mc_fixity = Infix} -> True + _ -> False + +-- | Guarded Right-Hand Sides +-- +-- GRHSs are used both for pattern bindings and for Matches +-- +-- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnVbar', +-- 'GHC.Parser.Annotation.AnnEqual','GHC.Parser.Annotation.AnnWhere', +-- 'GHC.Parser.Annotation.AnnOpen','GHC.Parser.Annotation.AnnClose' +-- 'GHC.Parser.Annotation.AnnRarrow','GHC.Parser.Annotation.AnnSemi' + +-- For details on above see note [Api annotations] in GHC.Parser.Annotation +data GRHSs p body + = GRHSs { + grhssExt :: XCGRHSs p body, + grhssGRHSs :: [LGRHS p body], -- ^ Guarded RHSs + grhssLocalBinds :: LHsLocalBinds p -- ^ The where clause + } + | XGRHSs !(XXGRHSs p body) + +-- | Located Guarded Right-Hand Side +type LGRHS id body = XRec id (GRHS id body) + +-- | Guarded Right Hand Side. +data GRHS p body = GRHS (XCGRHS p body) + [GuardLStmt p] -- Guards + body -- Right hand side + | XGRHS !(XXGRHS p body) + +-- We know the list must have at least one @Match@ in it. + +{- +************************************************************************ +* * +\subsection{Do stmts and list comprehensions} +* * +************************************************************************ +-} + +-- | Located @do@ block Statement +type LStmt id body = XRec id (StmtLR id id body) + +-- | Located Statement with separate Left and Right id's +type LStmtLR idL idR body = XRec idL (StmtLR idL idR body) + +-- | @do@ block Statement +type Stmt id body = StmtLR id id body + +-- | Command Located Statement +type CmdLStmt id = LStmt id (LHsCmd id) + +-- | Command Statement +type CmdStmt id = Stmt id (LHsCmd id) + +-- | Expression Located Statement +type ExprLStmt id = LStmt id (LHsExpr id) + +-- | Expression Statement +type ExprStmt id = Stmt id (LHsExpr id) + +-- | Guard Located Statement +type GuardLStmt id = LStmt id (LHsExpr id) + +-- | Guard Statement +type GuardStmt id = Stmt id (LHsExpr id) + +-- | Ghci Located Statement +type GhciLStmt id = LStmt id (LHsExpr id) + +-- | Ghci Statement +type GhciStmt id = Stmt id (LHsExpr id) + +-- The SyntaxExprs in here are used *only* for do-notation and monad +-- comprehensions, which have rebindable syntax. Otherwise they are unused. +-- | API Annotations when in qualifier lists or guards +-- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnVbar', +-- 'GHC.Parser.Annotation.AnnComma','GHC.Parser.Annotation.AnnThen', +-- 'GHC.Parser.Annotation.AnnBy','GHC.Parser.Annotation.AnnBy', +-- 'GHC.Parser.Annotation.AnnGroup','GHC.Parser.Annotation.AnnUsing' + +-- For details on above see note [Api annotations] in GHC.Parser.Annotation +data StmtLR idL idR body -- body should always be (LHs**** idR) + = LastStmt -- Always the last Stmt in ListComp, MonadComp, + -- and (after the renamer, see GHC.Rename.Expr.checkLastStmt) DoExpr, MDoExpr + -- Not used for GhciStmtCtxt, PatGuard, which scope over other stuff + (XLastStmt idL idR body) + body + (Maybe Bool) -- Whether return was stripped + -- Just True <=> return with a dollar was stripped by ApplicativeDo + -- Just False <=> return without a dollar was stripped by ApplicativeDo + -- Nothing <=> Nothing was stripped + (SyntaxExpr idR) -- The return operator + -- The return operator is used only for MonadComp + -- For ListComp we use the baked-in 'return' + -- For DoExpr, MDoExpr, we don't apply a 'return' at all + -- See Note [Monad Comprehensions] + -- - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLarrow' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | BindStmt (XBindStmt idL idR body) + -- ^ Post renaming has optional fail and bind / (>>=) operator. + -- Post typechecking, also has multiplicity of the argument + -- and the result type of the function passed to bind; + -- that is, (P, S) in (>>=) :: Q -> (R # P -> S) -> T + -- See Note [The type of bind in Stmts] + (LPat idL) + body + + -- | 'ApplicativeStmt' represents an applicative expression built with + -- '<$>' and '<*>'. It is generated by the renamer, and is desugared into the + -- appropriate applicative expression by the desugarer, but it is intended + -- to be invisible in error messages. + -- + -- For full details, see Note [ApplicativeDo] in "GHC.Rename.Expr" + -- + | ApplicativeStmt + (XApplicativeStmt idL idR body) -- Post typecheck, Type of the body + [ ( SyntaxExpr idR + , ApplicativeArg idL) ] + -- [(<$>, e1), (<*>, e2), ..., (<*>, en)] + (Maybe (SyntaxExpr idR)) -- 'join', if necessary + + | BodyStmt (XBodyStmt idL idR body) -- Post typecheck, element type + -- of the RHS (used for arrows) + body -- See Note [BodyStmt] + (SyntaxExpr idR) -- The (>>) operator + (SyntaxExpr idR) -- The `guard` operator; used only in MonadComp + -- See notes [Monad Comprehensions] + + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnLet' + -- 'GHC.Parser.Annotation.AnnOpen' @'{'@,'GHC.Parser.Annotation.AnnClose' @'}'@, + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | LetStmt (XLetStmt idL idR body) (LHsLocalBindsLR idL idR) + + -- ParStmts only occur in a list/monad comprehension + | ParStmt (XParStmt idL idR body) -- Post typecheck, + -- S in (>>=) :: Q -> (R -> S) -> T + [ParStmtBlock idL idR] + (HsExpr idR) -- Polymorphic `mzip` for monad comprehensions + (SyntaxExpr idR) -- The `>>=` operator + -- See notes [Monad Comprehensions] + -- After renaming, the ids are the binders + -- bound by the stmts and used after themp + + | TransStmt { + trS_ext :: XTransStmt idL idR body, -- Post typecheck, + -- R in (>>=) :: Q -> (R -> S) -> T + trS_form :: TransForm, + trS_stmts :: [ExprLStmt idL], -- Stmts to the *left* of the 'group' + -- which generates the tuples to be grouped + + trS_bndrs :: [(IdP idR, IdP idR)], -- See Note [TransStmt binder map] + + trS_using :: LHsExpr idR, + trS_by :: Maybe (LHsExpr idR), -- "by e" (optional) + -- Invariant: if trS_form = GroupBy, then grp_by = Just e + + trS_ret :: SyntaxExpr idR, -- The monomorphic 'return' function for + -- the inner monad comprehensions + trS_bind :: SyntaxExpr idR, -- The '(>>=)' operator + trS_fmap :: HsExpr idR -- The polymorphic 'fmap' function for desugaring + -- Only for 'group' forms + -- Just a simple HsExpr, because it's + -- too polymorphic for tcSyntaxOp + } -- See Note [Monad Comprehensions] + + -- Recursive statement (see Note [How RecStmt works] below) + -- | - 'GHC.Parser.Annotation.AnnKeywordId' : 'GHC.Parser.Annotation.AnnRec' + + -- For details on above see note [Api annotations] in GHC.Parser.Annotation + | RecStmt + { recS_ext :: XRecStmt idL idR body + , recS_stmts :: [LStmtLR idL idR body] + + -- The next two fields are only valid after renaming + , recS_later_ids :: [IdP idR] + -- The ids are a subset of the variables bound by the + -- stmts that are used in stmts that follow the RecStmt + + , recS_rec_ids :: [IdP idR] + -- Ditto, but these variables are the "recursive" ones, + -- that are used before they are bound in the stmts of + -- the RecStmt. + -- An Id can be in both groups + -- Both sets of Ids are (now) treated monomorphically + -- See Note [How RecStmt works] for why they are separate + + -- Rebindable syntax + , recS_bind_fn :: SyntaxExpr idR -- The bind function + , recS_ret_fn :: SyntaxExpr idR -- The return function + , recS_mfix_fn :: SyntaxExpr idR -- The mfix function + } + | XStmtLR !(XXStmtLR idL idR body) + +data TransForm -- The 'f' below is the 'using' function, 'e' is the by function + = ThenForm -- then f or then f by e (depending on trS_by) + | GroupForm -- then group using f or then group by e using f (depending on trS_by) + deriving Data + +-- | Parenthesised Statement Block +data ParStmtBlock idL idR + = ParStmtBlock + (XParStmtBlock idL idR) + [ExprLStmt idL] + [IdP idR] -- The variables to be returned + (SyntaxExpr idR) -- The return operator + | XParStmtBlock !(XXParStmtBlock idL idR) + +-- | The fail operator +-- +-- This is used for `.. <-` "bind statments" in do notation, including +-- non-monadic "binds" in applicative. +-- +-- The fail operator is 'Just expr' if it potentially fail monadically. if the +-- pattern match cannot fail, or shouldn't fail monadically (regular incomplete +-- pattern exception), it is 'Nothing'. +-- +-- See Note [Monad fail : Rebindable syntax, overloaded strings] for the type of +-- expression in the 'Just' case, and why it is so. +-- +-- See Note [Failing pattern matches in Stmts] for which contexts for +-- '@BindStmt@'s should use the monadic fail and which shouldn't. +type FailOperator id = Maybe (SyntaxExpr id) + +-- | Applicative Argument +data ApplicativeArg idL + = ApplicativeArgOne -- A single statement (BindStmt or BodyStmt) + { xarg_app_arg_one :: XApplicativeArgOne idL + -- ^ The fail operator, after renaming + -- + -- The fail operator is needed if this is a BindStmt + -- where the pattern can fail. E.g.: + -- (Just a) <- stmt + -- The fail operator will be invoked if the pattern + -- match fails. + -- It is also used for guards in MonadComprehensions. + -- The fail operator is Nothing + -- if the pattern match can't fail + , app_arg_pattern :: LPat idL -- WildPat if it was a BodyStmt (see below) + , arg_expr :: LHsExpr idL + , is_body_stmt :: Bool + -- ^ True <=> was a BodyStmt, + -- False <=> was a BindStmt. + -- See Note [Applicative BodyStmt] + } + | ApplicativeArgMany -- do { stmts; return vars } + { xarg_app_arg_many :: XApplicativeArgMany idL + , app_stmts :: [ExprLStmt idL] -- stmts + , final_expr :: HsExpr idL -- return (v1,..,vn), or just (v1,..,vn) + , bv_pattern :: LPat idL -- (v1,...,vn) + , stmt_context :: HsStmtContext (ApplicativeArgStmCtxPass idL) + -- ^ context of the do expression, used in pprArg + } + | XApplicativeArg !(XXApplicativeArg idL) + +type family ApplicativeArgStmCtxPass idL + +{- +Note [The type of bind in Stmts] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Some Stmts, notably BindStmt, keep the (>>=) bind operator. +We do NOT assume that it has type + (>>=) :: m a -> (a -> m b) -> m b +In some cases (see #303, #1537) it might have a more +exotic type, such as + (>>=) :: m i j a -> (a -> m j k b) -> m i k b +So we must be careful not to make assumptions about the type. +In particular, the monad may not be uniform throughout. + +Note [TransStmt binder map] +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The [(idR,idR)] in a TransStmt behaves as follows: + + * Before renaming: [] + + * After renaming: + [ (x27,x27), ..., (z35,z35) ] + These are the variables + bound by the stmts to the left of the 'group' + and used either in the 'by' clause, + or in the stmts following the 'group' + Each item is a pair of identical variables. + + * After typechecking: + [ (x27:Int, x27:[Int]), ..., (z35:Bool, z35:[Bool]) ] + Each pair has the same unique, but different *types*. + +Note [BodyStmt] +~~~~~~~~~~~~~~~ +BodyStmts are a bit tricky, because what they mean +depends on the context. Consider the following contexts: + + A do expression of type (m res_ty) + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * BodyStmt E any_ty: do { ....; E; ... } + E :: m any_ty + Translation: E >> ... + + A list comprehensions of type [elt_ty] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * BodyStmt E Bool: [ .. | .... E ] + [ .. | ..., E, ... ] + [ .. | .... | ..., E | ... ] + E :: Bool + Translation: if E then fail else ... + + A guard list, guarding a RHS of type rhs_ty + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * BodyStmt E BooParStmtBlockl: f x | ..., E, ... = ...rhs... + E :: Bool + Translation: if E then fail else ... + + A monad comprehension of type (m res_ty) + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + * BodyStmt E Bool: [ .. | .... E ] + E :: Bool + Translation: guard E >> ... + +Array comprehensions are handled like list comprehensions. + +Note [How RecStmt works] +~~~~~~~~~~~~~~~~~~~~~~~~ +Example: + HsDo [ BindStmt x ex + + , RecStmt { recS_rec_ids = [a, c] + , recS_stmts = [ BindStmt b (return (a,c)) + , LetStmt a = ...b... + , BindStmt c ec ] + , recS_later_ids = [a, b] + + , return (a b) ] + +Here, the RecStmt binds a,b,c; but + - Only a,b are used in the stmts *following* the RecStmt, + - Only a,c are used in the stmts *inside* the RecStmt + *before* their bindings + +Why do we need *both* rec_ids and later_ids? For monads they could be +combined into a single set of variables, but not for arrows. That +follows from the types of the respective feedback operators: + + mfix :: MonadFix m => (a -> m a) -> m a + loop :: ArrowLoop a => a (b,d) (c,d) -> a b c + +* For mfix, the 'a' covers the union of the later_ids and the rec_ids +* For 'loop', 'c' is the later_ids and 'd' is the rec_ids + +Note [Typing a RecStmt] +~~~~~~~~~~~~~~~~~~~~~~~ +A (RecStmt stmts) types as if you had written + + (v1,..,vn, _, ..., _) <- mfix (\~(_, ..., _, r1, ..., rm) -> + do { stmts + ; return (v1,..vn, r1, ..., rm) }) + +where v1..vn are the later_ids + r1..rm are the rec_ids + +Note [Monad Comprehensions] +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Monad comprehensions require separate functions like 'return' and +'>>=' for desugaring. These functions are stored in the statements +used in monad comprehensions. For example, the 'return' of the 'LastStmt' +expression is used to lift the body of the monad comprehension: + + [ body | stmts ] + => + stmts >>= \bndrs -> return body + +In transform and grouping statements ('then ..' and 'then group ..') the +'return' function is required for nested monad comprehensions, for example: + + [ body | stmts, then f, rest ] + => + f [ env | stmts ] >>= \bndrs -> [ body | rest ] + +BodyStmts require the 'Control.Monad.guard' function for boolean +expressions: + + [ body | exp, stmts ] + => + guard exp >> [ body | stmts ] + +Parallel statements require the 'Control.Monad.Zip.mzip' function: + + [ body | stmts1 | stmts2 | .. ] + => + mzip stmts1 (mzip stmts2 (..)) >>= \(bndrs1, (bndrs2, ..)) -> return body + +In any other context than 'MonadComp', the fields for most of these +'SyntaxExpr's stay bottom. + + +Note [Applicative BodyStmt] + +(#12143) For the purposes of ApplicativeDo, we treat any BodyStmt +as if it was a BindStmt with a wildcard pattern. For example, + + do + x <- A + B + return x + +is transformed as if it were + + do + x <- A + _ <- B + return x + +so it transforms to + + (\(x,_) -> x) <$> A <*> B + +But we have to remember when we treat a BodyStmt like a BindStmt, +because in error messages we want to emit the original syntax the user +wrote, not our internal representation. So ApplicativeArgOne has a +Bool flag that is True when the original statement was a BodyStmt, so +that we can pretty-print it correctly. +-} + + +{- +************************************************************************ +* * + Template Haskell quotation brackets +* * +************************************************************************ +-} + +-- | Haskell Splice +data HsSplice id + = HsTypedSplice -- $$z or $$(f 4) + (XTypedSplice id) + SpliceDecoration -- Whether $$( ) variant found, for pretty printing + (IdP id) -- A unique name to identify this splice point + (LHsExpr id) -- See Note [Pending Splices] + + | HsUntypedSplice -- $z or $(f 4) + (XUntypedSplice id) + SpliceDecoration -- Whether $( ) variant found, for pretty printing + (IdP id) -- A unique name to identify this splice point + (LHsExpr id) -- See Note [Pending Splices] + + | HsQuasiQuote -- See Note [Quasi-quote overview] in GHC.Tc.Gen.Splice + (XQuasiQuote id) + (IdP id) -- Splice point + (IdP id) -- Quoter + SrcSpan -- The span of the enclosed string + FastString -- The enclosed string + + -- AZ:TODO: use XSplice instead of HsSpliced + | HsSpliced -- See Note [Delaying modFinalizers in untyped splices] in + -- GHC.Rename.Splice. + -- This is the result of splicing a splice. It is produced by + -- the renamer and consumed by the typechecker. It lives only + -- between the two. + (XSpliced id) + ThModFinalizers -- TH finalizers produced by the splice. + (HsSplicedThing id) -- The result of splicing + | XSplice !(XXSplice id) -- Note [Trees that Grow] extension point + +-- | A splice can appear with various decorations wrapped around it. This data +-- type captures explicitly how it was originally written, for use in the pretty +-- printer. +data SpliceDecoration + = DollarSplice -- ^ $splice or $$splice + | BareSplice -- ^ bare splice + deriving (Data, Eq, Show) + +instance Outputable SpliceDecoration where + ppr x = text $ show x + + +isTypedSplice :: HsSplice id -> Bool +isTypedSplice (HsTypedSplice {}) = True +isTypedSplice _ = False -- Quasi-quotes are untyped splices + +-- | Finalizers produced by a splice with +-- 'Language.Haskell.TH.Syntax.addModFinalizer' +-- +-- See Note [Delaying modFinalizers in untyped splices] in GHC.Rename.Splice. For how +-- this is used. +-- +newtype ThModFinalizers = ThModFinalizers [ForeignRef (TH.Q ())] + +-- A Data instance which ignores the argument of 'ThModFinalizers'. +instance Data ThModFinalizers where + gunfold _ z _ = z $ ThModFinalizers [] + toConstr a = mkConstr (dataTypeOf a) "ThModFinalizers" [] Data.Prefix + dataTypeOf a = mkDataType "HsExpr.ThModFinalizers" [toConstr a] + +-- | Haskell Spliced Thing +-- +-- Values that can result from running a splice. +data HsSplicedThing id + = HsSplicedExpr (HsExpr id) -- ^ Haskell Spliced Expression + | HsSplicedTy (HsType id) -- ^ Haskell Spliced Type + | HsSplicedPat (Pat id) -- ^ Haskell Spliced Pattern + + +-- See Note [Pending Splices] +type SplicePointName = Name + +data UntypedSpliceFlavour + = UntypedExpSplice + | UntypedPatSplice + | UntypedTypeSplice + | UntypedDeclSplice + deriving Data + +-- | Haskell Bracket +data HsBracket p + = ExpBr (XExpBr p) (LHsExpr p) -- [| expr |] + | PatBr (XPatBr p) (LPat p) -- [p| pat |] + | DecBrL (XDecBrL p) [LHsDecl p] -- [d| decls |]; result of parser + | DecBrG (XDecBrG p) (HsGroup p) -- [d| decls |]; result of renamer + | TypBr (XTypBr p) (LHsType p) -- [t| type |] + | VarBr (XVarBr p) Bool (IdP p) -- True: 'x, False: ''T + -- (The Bool flag is used only in pprHsBracket) + | TExpBr (XTExpBr p) (LHsExpr p) -- [|| expr ||] + | XBracket !(XXBracket p) -- Note [Trees that Grow] extension point + +isTypedBracket :: HsBracket id -> Bool +isTypedBracket (TExpBr {}) = True +isTypedBracket _ = False + +{- +************************************************************************ +* * +\subsection{Enumerations and list comprehensions} +* * +************************************************************************ +-} + +-- | Arithmetic Sequence Information +data ArithSeqInfo id + = From (LHsExpr id) + | FromThen (LHsExpr id) + (LHsExpr id) + | FromTo (LHsExpr id) + (LHsExpr id) + | FromThenTo (LHsExpr id) + (LHsExpr id) + (LHsExpr id) +-- AZ: Should ArithSeqInfo have a TTG extension? + +{- +************************************************************************ +* * +\subsection{HsMatchCtxt} +* * +************************************************************************ +-} + +-- | Haskell Match Context +-- +-- Context of a pattern match. This is more subtle than it would seem. See Note +-- [Varieties of pattern matches]. +data HsMatchContext p + = FunRhs { mc_fun :: LIdP p -- ^ function binder of @f@ + , mc_fixity :: LexicalFixity -- ^ fixing of @f@ + , mc_strictness :: SrcStrictness -- ^ was @f@ banged? + -- See Note [FunBind vs PatBind] + } + -- ^A pattern matching on an argument of a + -- function binding + | LambdaExpr -- ^Patterns of a lambda + | CaseAlt -- ^Patterns and guards on a case alternative + | IfAlt -- ^Guards of a multi-way if alternative + | ProcExpr -- ^Patterns of a proc + | PatBindRhs -- ^A pattern binding eg [y] <- e = e + | PatBindGuards -- ^Guards of pattern bindings, e.g., + -- (Just b) | Just _ <- x = e + -- | otherwise = e' + + | RecUpd -- ^Record update [used only in GHC.HsToCore.Expr to + -- tell matchWrapper what sort of + -- runtime error message to generate] + + | StmtCtxt (HsStmtContext p) -- ^Pattern of a do-stmt, list comprehension, + -- pattern guard, etc + + | ThPatSplice -- ^A Template Haskell pattern splice + | ThPatQuote -- ^A Template Haskell pattern quotation [p| (a,b) |] + | PatSyn -- ^A pattern synonym declaration + +isPatSynCtxt :: HsMatchContext p -> Bool +isPatSynCtxt ctxt = + case ctxt of + PatSyn -> True + _ -> False + +-- | Haskell Statement Context. +data HsStmtContext p + = ListComp + | MonadComp + + | DoExpr (Maybe ModuleName) -- ^[ModuleName.]do { ... } + | MDoExpr (Maybe ModuleName) -- ^[ModuleName.]mdo { ... } ie recursive do-expression + | ArrowExpr -- ^do-notation in an arrow-command context + + | GhciStmtCtxt -- ^A command-line Stmt in GHCi pat <- rhs + | PatGuard (HsMatchContext p) -- ^Pattern guard for specified thing + | ParStmtCtxt (HsStmtContext p) -- ^A branch of a parallel stmt + | TransStmtCtxt (HsStmtContext p) -- ^A branch of a transform stmt + +qualifiedDoModuleName_maybe :: HsStmtContext p -> Maybe ModuleName +qualifiedDoModuleName_maybe ctxt = case ctxt of + DoExpr m -> m + MDoExpr m -> m + _ -> Nothing + +isComprehensionContext :: HsStmtContext id -> Bool +-- Uses comprehension syntax [ e | quals ] +isComprehensionContext ListComp = True +isComprehensionContext MonadComp = True +isComprehensionContext (ParStmtCtxt c) = isComprehensionContext c +isComprehensionContext (TransStmtCtxt c) = isComprehensionContext c +isComprehensionContext _ = False + +-- | Is this a monadic context? +isMonadStmtContext :: HsStmtContext id -> Bool +isMonadStmtContext MonadComp = True +isMonadStmtContext DoExpr{} = True +isMonadStmtContext MDoExpr{} = True +isMonadStmtContext GhciStmtCtxt = True +isMonadStmtContext (ParStmtCtxt ctxt) = isMonadStmtContext ctxt +isMonadStmtContext (TransStmtCtxt ctxt) = isMonadStmtContext ctxt +isMonadStmtContext _ = False -- ListComp, PatGuard, ArrowExpr + +isMonadCompContext :: HsStmtContext id -> Bool +isMonadCompContext MonadComp = True +isMonadCompContext _ = False + +matchSeparator :: HsMatchContext p -> SDoc +matchSeparator (FunRhs {}) = text "=" +matchSeparator CaseAlt = text "->" +matchSeparator IfAlt = text "->" +matchSeparator LambdaExpr = text "->" +matchSeparator ProcExpr = text "->" +matchSeparator PatBindRhs = text "=" +matchSeparator PatBindGuards = text "=" +matchSeparator (StmtCtxt _) = text "<-" +matchSeparator RecUpd = text "=" -- This can be printed by the pattern + -- match checker trace +matchSeparator ThPatSplice = panic "unused" +matchSeparator ThPatQuote = panic "unused" +matchSeparator PatSyn = panic "unused" + +pprMatchContext :: (Outputable (IdP p), UnXRec p) + => HsMatchContext p -> SDoc +pprMatchContext ctxt + | want_an ctxt = text "an" <+> pprMatchContextNoun ctxt + | otherwise = text "a" <+> pprMatchContextNoun ctxt + where + want_an (FunRhs {}) = True -- Use "an" in front + want_an ProcExpr = True + want_an _ = False + +pprMatchContextNoun :: forall p. (Outputable (IdP p), UnXRec p) + => HsMatchContext p -> SDoc +pprMatchContextNoun (FunRhs {mc_fun=fun}) + = text "equation for" + <+> quotes (ppr (unXRec @p fun)) +pprMatchContextNoun CaseAlt = text "case alternative" +pprMatchContextNoun IfAlt = text "multi-way if alternative" +pprMatchContextNoun RecUpd = text "record-update construct" +pprMatchContextNoun ThPatSplice = text "Template Haskell pattern splice" +pprMatchContextNoun ThPatQuote = text "Template Haskell pattern quotation" +pprMatchContextNoun PatBindRhs = text "pattern binding" +pprMatchContextNoun PatBindGuards = text "pattern binding guards" +pprMatchContextNoun LambdaExpr = text "lambda abstraction" +pprMatchContextNoun ProcExpr = text "arrow abstraction" +pprMatchContextNoun (StmtCtxt ctxt) = text "pattern binding in" + $$ pprAStmtContext ctxt +pprMatchContextNoun PatSyn = text "pattern synonym declaration" + +----------------- +pprAStmtContext, pprStmtContext :: (Outputable (IdP p), UnXRec p) + => HsStmtContext p -> SDoc +pprAStmtContext ctxt = article <+> pprStmtContext ctxt + where + pp_an = text "an" + pp_a = text "a" + article = case ctxt of + MDoExpr Nothing -> pp_an + GhciStmtCtxt -> pp_an + _ -> pp_a + + +----------------- +pprStmtContext GhciStmtCtxt = text "interactive GHCi command" +pprStmtContext (DoExpr m) = prependQualified m (text "'do' block") +pprStmtContext (MDoExpr m) = prependQualified m (text "'mdo' block") +pprStmtContext ArrowExpr = text "'do' block in an arrow command" +pprStmtContext ListComp = text "list comprehension" +pprStmtContext MonadComp = text "monad comprehension" +pprStmtContext (PatGuard ctxt) = text "pattern guard for" $$ pprMatchContext ctxt + +-- Drop the inner contexts when reporting errors, else we get +-- Unexpected transform statement +-- in a transformed branch of +-- transformed branch of +-- transformed branch of monad comprehension +pprStmtContext (ParStmtCtxt c) = + ifPprDebug (sep [text "parallel branch of", pprAStmtContext c]) + (pprStmtContext c) +pprStmtContext (TransStmtCtxt c) = + ifPprDebug (sep [text "transformed branch of", pprAStmtContext c]) + (pprStmtContext c) + +prependQualified :: Maybe ModuleName -> SDoc -> SDoc +prependQualified Nothing t = t +prependQualified (Just _) t = text "qualified" <+> t |