path: root/compiler/hsSyn/HsUtils.lhs

%
% (c) The University of Glasgow, 1992-2006
%

Here we collect a variety of helper functions that construct or
analyse HsSyn.  All these functions deal with generic HsSyn; functions
which deal with the intantiated versions are located elsewhere:

   Parameterised by	Module
   ----------------     -------------
   RdrName		parser/RdrHsSyn
   Name			rename/RnHsSyn
   Id			typecheck/TcHsSyn	

\begin{code}
{-# OPTIONS_GHC -w #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--     http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
-- for details

module HsUtils where

#include "HsVersions.h"

import HsBinds
import HsExpr
import HsPat
import HsTypes	
import HsLit

import RdrName
import Var
import Type
import DataCon
import Name
import BasicTypes
import SrcLoc
import FastString
import Outputable
import Util
import Bag
\end{code}


%************************************************************************
%*									*
	Some useful helpers for constructing syntax
%*									*
%************************************************************************

These functions attempt to construct a not-completely-useless SrcSpan
from their components, compared with the nl* functions below which
just attach noSrcSpan to everything.

\begin{code}
mkHsPar :: LHsExpr id -> LHsExpr id
mkHsPar e = L (getLoc e) (HsPar e)

mkSimpleMatch :: [LPat id] -> LHsExpr id -> LMatch id
mkSimpleMatch pats rhs 
  = L loc $
    Match pats Nothing (unguardedGRHSs rhs)
  where
    loc = case pats of
		[]      -> getLoc rhs
		(pat:_) -> combineSrcSpans (getLoc pat) (getLoc rhs)

unguardedGRHSs :: LHsExpr id -> GRHSs id
unguardedGRHSs rhs = GRHSs (unguardedRHS rhs) emptyLocalBinds

unguardedRHS :: LHsExpr id -> [LGRHS id]
unguardedRHS rhs@(L loc _) = [L loc (GRHS [] rhs)]

mkHsAppTy :: LHsType name -> LHsType name -> LHsType name
mkHsAppTy t1 t2 = addCLoc t1 t2 (HsAppTy t1 t2)

mkHsApp :: LHsExpr name -> LHsExpr name -> LHsExpr name
mkHsApp e1 e2 = addCLoc e1 e2 (HsApp e1 e2)

nlHsTyApp :: name -> [Type] -> LHsExpr name
nlHsTyApp fun_id tys = noLoc (HsWrap (mkWpTyApps tys) (HsVar fun_id))

mkLHsWrap :: HsWrapper -> LHsExpr id -> LHsExpr id
mkLHsWrap co_fn (L loc e) = L loc (mkHsWrap co_fn e)

mkHsWrap :: HsWrapper -> HsExpr id -> HsExpr id
mkHsWrap co_fn e | isIdHsWrapper co_fn = e
		 | otherwise	      = HsWrap co_fn e

mkHsLam :: [LPat id] -> LHsExpr id -> LHsExpr id
mkHsLam pats body = mkHsPar (L (getLoc body) (HsLam matches))
	where
	  matches = mkMatchGroup [mkSimpleMatch pats body]

mkMatchGroup :: [LMatch id] -> MatchGroup id
mkMatchGroup matches = MatchGroup matches placeHolderType

mkHsDictLet :: LHsBinds Id -> LHsExpr Id -> LHsExpr Id
-- Used for the dictionary bindings gotten from TcSimplify
-- We make them recursive to be on the safe side
mkHsDictLet binds expr 
  | isEmptyLHsBinds binds = expr
  | otherwise             = L (getLoc expr) (HsLet (HsValBinds val_binds) expr)
			  where
			    val_binds = ValBindsOut [(Recursive, binds)] []

mkHsConApp :: DataCon -> [Type] -> [HsExpr Id] -> LHsExpr Id
-- Used for constructing dictionary terms etc, so no locations 
mkHsConApp data_con tys args 
  = foldl mk_app (nlHsTyApp (dataConWrapId data_con) tys) args
  where
    mk_app f a = noLoc (HsApp f (noLoc a))

mkSimpleHsAlt :: LPat id -> LHsExpr id -> LMatch id
-- A simple lambda with a single pattern, no binds, no guards; pre-typechecking
mkSimpleHsAlt pat expr 
  = mkSimpleMatch [pat] expr

-------------------------------
-- These are the bits of syntax that contain rebindable names
-- See RnEnv.lookupSyntaxName

mkHsIntegral   i       = HsIntegral   i  noSyntaxExpr
mkHsFractional f       = HsFractional f  noSyntaxExpr
mkHsIsString   s       = HsIsString   s  noSyntaxExpr
mkHsDo ctxt stmts body = HsDo ctxt stmts body placeHolderType

mkNPat lit neg     = NPat lit neg noSyntaxExpr placeHolderType
mkNPlusKPat id lit = NPlusKPat id lit noSyntaxExpr noSyntaxExpr

mkExprStmt expr	    = ExprStmt expr noSyntaxExpr placeHolderType
mkBindStmt pat expr = BindStmt pat expr noSyntaxExpr noSyntaxExpr
mkRecStmt stmts	    = RecStmt stmts [] [] [] emptyLHsBinds

-------------------------------
--- A useful function for building @OpApps@.  The operator is always a
-- variable, and we don't know the fixity yet.
mkHsOpApp e1 op e2 = OpApp e1 (noLoc (HsVar op)) (error "mkOpApp:fixity") e2

mkHsSplice e = HsSplice unqualSplice e

unqualSplice = mkRdrUnqual (mkVarOccFS FSLIT("splice"))
		-- A name (uniquified later) to
		-- identify the splice

mkHsString s = HsString (mkFastString s)

-------------
userHsTyVarBndrs :: [Located name] -> [Located (HsTyVarBndr name)]
userHsTyVarBndrs bndrs = [ L loc (UserTyVar v) | L loc v <- bndrs ]
\end{code}


%************************************************************************
%*									*
	Constructing syntax with no location info
%*									*
%************************************************************************

\begin{code}
nlHsVar :: id -> LHsExpr id
nlHsVar n = noLoc (HsVar n)

nlHsLit :: HsLit -> LHsExpr id
nlHsLit n = noLoc (HsLit n)

nlVarPat :: id -> LPat id
nlVarPat n = noLoc (VarPat n)

nlLitPat :: HsLit -> LPat id
nlLitPat l = noLoc (LitPat l)

nlHsApp :: LHsExpr id -> LHsExpr id -> LHsExpr id
nlHsApp f x = noLoc (HsApp f x)

nlHsIntLit n = noLoc (HsLit (HsInt n))

nlHsApps :: id -> [LHsExpr id] -> LHsExpr id
nlHsApps f xs = foldl nlHsApp (nlHsVar f) xs
	     
nlHsVarApps :: id -> [id] -> LHsExpr id
nlHsVarApps f xs = noLoc (foldl mk (HsVar f) (map HsVar xs))
		 where
		   mk f a = HsApp (noLoc f) (noLoc a)

nlConVarPat :: id -> [id] -> LPat id
nlConVarPat con vars = nlConPat con (map nlVarPat vars)

nlInfixConPat :: id -> LPat id -> LPat id -> LPat id
nlInfixConPat con l r = noLoc (ConPatIn (noLoc con) (InfixCon l r))

nlConPat :: id -> [LPat id] -> LPat id
nlConPat con pats = noLoc (ConPatIn (noLoc con) (PrefixCon pats))

nlNullaryConPat :: id -> LPat id
nlNullaryConPat con = noLoc (ConPatIn (noLoc con) (PrefixCon []))

nlWildConPat :: DataCon -> LPat RdrName
nlWildConPat con = noLoc (ConPatIn (noLoc (getRdrName con))
				   (PrefixCon (nOfThem (dataConSourceArity con) nlWildPat)))

nlTuplePat pats box = noLoc (TuplePat pats box placeHolderType)
nlWildPat  = noLoc (WildPat placeHolderType)	-- Pre-typechecking

nlHsDo :: HsStmtContext Name -> [LStmt id] -> LHsExpr id -> LHsExpr id
nlHsDo ctxt stmts body = noLoc (mkHsDo ctxt stmts body)

nlHsOpApp e1 op e2 = noLoc (mkHsOpApp e1 op e2)

nlHsLam	match		= noLoc (HsLam (mkMatchGroup [match]))
nlHsPar e		= noLoc (HsPar e)
nlHsIf cond true false	= noLoc (HsIf cond true false)
nlHsCase expr matches	= noLoc (HsCase expr (mkMatchGroup matches))
nlTuple exprs box	= noLoc (ExplicitTuple exprs box)
nlList exprs		= noLoc (ExplicitList placeHolderType exprs)

nlHsAppTy f t		= noLoc (HsAppTy f t)
nlHsTyVar x		= noLoc (HsTyVar x)
nlHsFunTy a b		= noLoc (HsFunTy a b)

nlHsTyConApp tycon tys  = foldl nlHsAppTy (nlHsTyVar tycon) tys
\end{code}



%************************************************************************
%*									*
		Bindings; with a location at the top
%*									*
%************************************************************************

\begin{code}
mkFunBind :: Located id -> [LMatch id] -> HsBind id
-- Not infix, with place holders for coercion and free vars
mkFunBind fn ms = FunBind { fun_id = fn, fun_infix = False, fun_matches = mkMatchGroup ms,
			    fun_co_fn = idHsWrapper, bind_fvs = placeHolderNames,
			    fun_tick = Nothing }


mkVarBind :: SrcSpan -> RdrName -> LHsExpr RdrName -> LHsBind RdrName
mkVarBind loc var rhs = mk_easy_FunBind loc var [] rhs

------------
mk_easy_FunBind :: SrcSpan -> RdrName -> [LPat RdrName]
		-> LHsExpr RdrName -> LHsBind RdrName

mk_easy_FunBind loc fun pats expr
  = L loc $ mkFunBind (L loc fun) [mkMatch pats expr emptyLocalBinds]

------------
mk_FunBind :: SrcSpan -> RdrName
	   -> [([LPat RdrName], LHsExpr RdrName)]
	   -> LHsBind RdrName

mk_FunBind loc fun [] = panic "TcGenDeriv:mk_FunBind"
mk_FunBind loc fun pats_and_exprs
  = L loc $ mkFunBind (L loc fun) matches
  where
    matches = [mkMatch p e emptyLocalBinds | (p,e) <-pats_and_exprs]

------------
mkMatch :: [LPat id] -> LHsExpr id -> HsLocalBinds id -> LMatch id
mkMatch pats expr binds
  = noLoc (Match (map paren pats) Nothing 
		 (GRHSs (unguardedRHS expr) binds))
  where
    paren p = case p of
		L _ (VarPat _) -> p
		L l _	       -> L l (ParPat p)
\end{code}


%************************************************************************
%*									*
	Collecting binders from HsBindGroups and HsBinds
%*									*
%************************************************************************

Get all the binders in some HsBindGroups, IN THE ORDER OF APPEARANCE. eg.

...
where
  (x, y) = ...
  f i j  = ...
  [a, b] = ...

it should return [x, y, f, a, b] (remember, order important).

\begin{code}
collectLocalBinders :: HsLocalBinds name -> [Located name]
collectLocalBinders (HsValBinds val_binds) = collectHsValBinders val_binds
collectLocalBinders (HsIPBinds _)   = []
collectLocalBinders EmptyLocalBinds = []

collectHsValBinders :: HsValBinds name -> [Located name]
collectHsValBinders (ValBindsIn binds sigs)  = collectHsBindLocatedBinders binds
collectHsValBinders (ValBindsOut binds sigs) = foldr collect_one [] binds
  where
   collect_one (_,binds) acc = foldrBag (collectAcc . unLoc) acc binds

collectAcc :: HsBind name -> [Located name] -> [Located name]
collectAcc (PatBind { pat_lhs = p }) acc = collectLocatedPatBinders p ++ acc
collectAcc (FunBind { fun_id = f })  acc    = f : acc
collectAcc (VarBind { var_id = f })  acc    = noLoc f : acc
collectAcc (AbsBinds { abs_exports = dbinds, abs_binds = binds }) acc
  = [noLoc dp | (_,dp,_,_) <- dbinds] ++ acc
	-- ++ foldr collectAcc acc binds
	-- I don't think we want the binders from the nested binds
	-- The only time we collect binders from a typechecked 
	-- binding (hence see AbsBinds) is in zonking in TcHsSyn

collectHsBindBinders :: LHsBinds name -> [name]
collectHsBindBinders binds = map unLoc (collectHsBindLocatedBinders binds)

collectHsBindLocatedBinders :: LHsBinds name -> [Located name]
collectHsBindLocatedBinders binds = foldrBag (collectAcc . unLoc) [] binds
\end{code}


%************************************************************************
%*									*
	Getting binders from statements
%*									*
%************************************************************************

\begin{code}
collectLStmtsBinders :: OutputableBndr id => [LStmt id] -> [Located id]
collectLStmtsBinders = concatMap collectLStmtBinders

collectStmtsBinders :: OutputableBndr id => [Stmt id] -> [Located id]
collectStmtsBinders = concatMap collectStmtBinders

collectLStmtBinders :: OutputableBndr id => LStmt id -> [Located id]
collectLStmtBinders = collectStmtBinders . unLoc

collectStmtBinders :: OutputableBndr id => Stmt id -> [Located id]
  -- Id Binders for a Stmt... [but what about pattern-sig type vars]?
collectStmtBinders (BindStmt pat _ _ _) = collectLocatedPatBinders pat
collectStmtBinders (LetStmt binds)      = collectLocalBinders binds
collectStmtBinders (ExprStmt _ _ _)     = []
collectStmtBinders (ParStmt xs)         = collectLStmtsBinders
                                        $ concatMap fst xs
collectStmtBinders (RecStmt ss _ _ _ _) = collectLStmtsBinders ss
collectStmtBinders s                    = pprPanic "collectStmtBinders" (ppr s)
\end{code}


%************************************************************************
%*									*
%* 	Gathering stuff out of patterns
%*									*
%************************************************************************

This function @collectPatBinders@ works with the ``collectBinders''
functions for @HsBinds@, etc.  The order in which the binders are
collected is important; see @HsBinds.lhs@.

It collects the bounds *value* variables in renamed patterns; type variables
are *not* collected.

\begin{code}
collectPatBinders :: LPat a -> [a]
collectPatBinders pat = map unLoc (collectLocatedPatBinders pat)

collectLocatedPatBinders :: LPat a -> [Located a]
collectLocatedPatBinders pat = collectl pat []

collectPatsBinders :: [LPat a] -> [a]
collectPatsBinders pats = map unLoc (collectLocatedPatsBinders pats)

collectLocatedPatsBinders :: [LPat a] -> [Located a]
collectLocatedPatsBinders pats = foldr collectl [] pats

---------------------
collectl (L l pat) bndrs
  = go pat
  where
    go (VarPat var) 	   	  = L l var : bndrs
    go (VarPatOut var bs) 	  = L l var : collectHsBindLocatedBinders bs 
				    ++ bndrs
    go (WildPat _)	      	  = bndrs
    go (LazyPat pat)     	  = collectl pat bndrs
    go (BangPat pat)     	  = collectl pat bndrs
    go (AsPat a pat)     	  = a : collectl pat bndrs
    go (ParPat  pat)     	  = collectl pat bndrs
				  
    go (ListPat pats _)    	  = foldr collectl bndrs pats
    go (PArrPat pats _)    	  = foldr collectl bndrs pats
    go (TuplePat pats _ _)  	  = foldr collectl bndrs pats
				  
    go (ConPatIn c ps)   	  = foldr collectl bndrs (hsConPatArgs ps)
    go (ConPatOut {pat_args=ps})  = foldr collectl bndrs (hsConPatArgs ps)
	-- See Note [Dictionary binders in ConPatOut]
    go (LitPat _)	      	  = bndrs
    go (NPat _ _ _ _)		  = bndrs
    go (NPlusKPat n _ _ _)        = n : bndrs
 				  
    go (SigPatIn pat _)	 	  = collectl pat bndrs
    go (SigPatOut pat _)	  = collectl pat bndrs
    go (TypePat ty)               = bndrs
    go (CoPat _ pat ty)           = collectl (noLoc pat) bndrs
\end{code}

Note [Dictionary binders in ConPatOut]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Do *not* gather (a) dictionary and (b) dictionary bindings as binders
of a ConPatOut pattern.  For most calls it doesn't matter, because
it's pre-typechecker and there are no ConPatOuts.  But it does matter
more in the desugarer; for example, DsUtils.mkSelectorBinds uses
collectPatBinders.  In a lazy pattern, for example f ~(C x y) = ...,
we want to generate bindings for x,y but not for dictionaries bound by
C.  (The type checker ensures they would not be used.)

Desugaring of arrow case expressions needs these bindings (see DsArrows
and arrowcase1), but SPJ (Jan 2007) says it's safer for it to use its
own pat-binder-collector:

Here's the problem.  Consider

data T a where
   C :: Num a => a -> Int -> T a

f ~(C (n+1) m) = (n,m)

Here, the pattern (C (n+1)) binds a hidden dictionary (d::Num a),
and *also* uses that dictionary to match the (n+1) pattern.  Yet, the
variables bound by the lazy pattern are n,m, *not* the dictionary d.
So in mkSelectorBinds in DsUtils, we want just m,n as the variables bound.

\begin{code}
collectSigTysFromPats :: [InPat name] -> [LHsType name]
collectSigTysFromPats pats = foldr collect_lpat [] pats

collectSigTysFromPat :: InPat name -> [LHsType name]
collectSigTysFromPat pat = collect_lpat pat []

collect_lpat pat acc = collect_pat (unLoc pat) acc

collect_pat (SigPatIn pat ty)  	acc = collect_lpat pat (ty:acc)
collect_pat (TypePat ty)       	acc = ty:acc

collect_pat (LazyPat pat)      	acc = collect_lpat pat acc
collect_pat (BangPat pat)      	acc = collect_lpat pat acc
collect_pat (AsPat a pat)      	acc = collect_lpat pat acc
collect_pat (ParPat  pat)      	acc = collect_lpat pat acc
collect_pat (ListPat pats _)   	acc = foldr collect_lpat acc pats
collect_pat (PArrPat pats _)   	acc = foldr collect_lpat acc pats
collect_pat (TuplePat pats _ _) acc = foldr collect_lpat acc pats
collect_pat (ConPatIn c ps)     acc = foldr collect_lpat acc (hsConPatArgs ps)
collect_pat other	        acc = acc 	-- Literals, vars, wildcard
\end{code}