diff options
Diffstat (limited to 'compiler/parser/Lexer.x')
| -rw-r--r-- | compiler/parser/Lexer.x | 48 |
1 files changed, 46 insertions, 2 deletions
diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x index cee8540c09..1bbbfbf20f 100644 --- a/compiler/parser/Lexer.x +++ b/compiler/parser/Lexer.x @@ -394,6 +394,14 @@ $tab { warnTab } { lex_qquasiquote_tok } } + -- See Note [Lexing type applications] +<0> { + [^ $idchar \) ] ^ + "@" + / { ifExtension typeApplicationEnabled `alexAndPred` notFollowedBySymbol } + { token ITtypeApp } +} + <0> { "(|" / { ifExtension arrowsEnabled `alexAndPred` notFollowedBySymbol } { special IToparenbar } @@ -507,6 +515,32 @@ $tab { warnTab } \" { lex_string_tok } } +-- Note [Lexing type applications] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- The desired syntax for type applications is to prefix the type application +-- with '@', like this: +-- +-- foo @Int @Bool baz bum +-- +-- This, of course, conflicts with as-patterns. The conflict arises because +-- expressions and patterns use the same parser, and also because we want +-- to allow type patterns within expression patterns. +-- +-- Disambiguation is accomplished by requiring *something* to appear betwen +-- type application and the preceding token. This something must end with +-- a character that cannot be the end of the variable bound in an as-pattern. +-- Currently (June 2015), this means that the something cannot end with a +-- $idchar or a close-paren. (The close-paren is necessary if the as-bound +-- identifier is symbolic.) +-- +-- Note that looking for whitespace before the '@' is insufficient, because +-- of this pathological case: +-- +-- foo {- hi -}@Int +-- +-- This design is predicated on the fact that as-patterns are generally +-- whitespace-free, and also that this whole thing is opt-in, with the +-- TypeApplications extension. -- ----------------------------------------------------------------------------- -- Alex "Haskell code fragment bottom" @@ -686,8 +720,13 @@ data Token | ITLarrowtail IsUnicodeSyntax -- -<< | ITRarrowtail IsUnicodeSyntax -- >>- - | ITunknown String -- Used when the lexer can't make sense of it - | ITeof -- end of file token + -- type application '@' (lexed differently than as-pattern '@', + -- due to checking for preceding whitespace) + | ITtypeApp + + + | ITunknown String -- Used when the lexer can't make sense of it + | ITeof -- end of file token -- Documentation annotations | ITdocCommentNext String -- something beginning '-- |' @@ -2023,6 +2062,7 @@ data ExtBits | LambdaCaseBit | BinaryLiteralsBit | NegativeLiteralsBit + | TypeApplicationsBit deriving Enum @@ -2083,6 +2123,8 @@ negativeLiteralsEnabled :: ExtsBitmap -> Bool negativeLiteralsEnabled = xtest NegativeLiteralsBit patternSynonymsEnabled :: ExtsBitmap -> Bool patternSynonymsEnabled = xtest PatternSynonymsBit +typeApplicationEnabled :: ExtsBitmap -> Bool +typeApplicationEnabled = xtest TypeApplicationsBit -- PState for parsing options pragmas -- @@ -2153,6 +2195,8 @@ mkPState flags buf loc = .|. BinaryLiteralsBit `setBitIf` xopt LangExt.BinaryLiterals flags .|. NegativeLiteralsBit `setBitIf` xopt LangExt.NegativeLiterals flags .|. PatternSynonymsBit `setBitIf` xopt LangExt.PatternSynonyms flags + .|. TypeApplicationsBit `setBitIf` xopt LangExt.TypeApplications flags + -- setBitIf :: ExtBits -> Bool -> ExtsBitmap b `setBitIf` cond | cond = xbit b |