[commit: ghc] type-holes-branch: Extended the parser to support "__", which will be used to denote a hole. (2f3e9e0)

Repository : ssh://darcs.haskell.org//srv/darcs/ghc

On branch  : type-holes-branch

http://hackage.haskell.org/trac/ghc/changeset/2f3e9e05f93669eb082ef05e7faf26cbabfc21d7

>---------------------------------------------------------------

commit 2f3e9e05f93669eb082ef05e7faf26cbabfc21d7
Author: Thijs Alkemade <[email protected]>
Date:   Fri Dec 2 09:53:21 2011 +0100

    Extended the parser to support "__", which will be used to denote a hole.

>---------------------------------------------------------------

 compiler/hsSyn/HsExpr.lhs     |    3 +++
 compiler/parser/Lexer.x       |    2 ++
 compiler/parser/Parser.y.pp   |    2 ++
 compiler/rename/RnExpr.lhs    |    3 +++
 compiler/typecheck/TcExpr.lhs |    2 ++
 5 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/compiler/hsSyn/HsExpr.lhs b/compiler/hsSyn/HsExpr.lhs
index 1dd3c83..121687c 100644
--- a/compiler/hsSyn/HsExpr.lhs
+++ b/compiler/hsSyn/HsExpr.lhs
@@ -290,6 +290,7 @@ data HsExpr id
 
   |  HsWrap     HsWrapper    -- TRANSLATION
                 (HsExpr id)
+  |  HsHole
   deriving (Data, Typeable)
 
 -- HsTupArg is used for tuple sections
@@ -545,6 +546,8 @@ ppr_expr (HsArrForm (L _ (HsVar v)) (Just _) [arg1, arg2])
 ppr_expr (HsArrForm op _ args)
   = hang (ptext (sLit "(|") <> ppr_lexpr op)
          4 (sep (map (pprCmdArg.unLoc) args) <> ptext (sLit "|)"))
+ppr_expr HsHole
+  = text "__"
 
 pprCmdArg :: OutputableBndr id => HsCmdTop id -> SDoc
 pprCmdArg (HsCmdTop cmd@(L _ (HsArrForm _ Nothing [])) _ _ _)
diff --git a/compiler/parser/Lexer.x b/compiler/parser/Lexer.x
index 21984ec..2595fc7 100644
--- a/compiler/parser/Lexer.x
+++ b/compiler/parser/Lexer.x
@@ -524,6 +524,7 @@ data Token
   | ITsemi
   | ITcomma
   | ITunderscore
+  | ITdoubleunderscore
   | ITbackquote
   | ITsimpleQuote               --  '
 
@@ -599,6 +600,7 @@ reservedWordsFM :: UniqFM (Token, Int)
 reservedWordsFM = listToUFM $
     map (\(x, y, z) -> (mkFastString x, (y, z)))
         [( "_",              ITunderscore,    0 ),
+         ( "__",          ITdoubleunderscore, 0 ),
          ( "as",             ITas,            0 ),
          ( "case",           ITcase,          0 ),
          ( "class",          ITclass,         0 ),
diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index 8a41fa4..3b3bbd4 100644
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -207,6 +207,7 @@ incorrect.
 
 %token
  '_'            { L _ ITunderscore }            -- Haskell keywords
+ '__'           { L _ ITdoubleunderscore }
  'as'           { L _ ITas }
  'case'         { L _ ITcase }          
  'class'        { L _ ITclass } 
@@ -1458,6 +1459,7 @@ aexp2   :: { LHsExpr RdrName }
         | '[' list ']'                  { LL (unLoc $2) }
         | '[:' parr ':]'                { LL (unLoc $2) }
         | '_'                           { L1 EWildPat }
+        | '__'                          { L1 HsHole }
         
         -- Template Haskell Extension
         | TH_ID_SPLICE          { L1 $ HsSpliceE (mkHsSplice 
diff --git a/compiler/rename/RnExpr.lhs b/compiler/rename/RnExpr.lhs
index 0487733..6773ed4 100644
--- a/compiler/rename/RnExpr.lhs
+++ b/compiler/rename/RnExpr.lhs
@@ -293,6 +293,9 @@ rnExpr (ArithSeq _ seq)
 rnExpr (PArrSeq _ seq)
   = rnArithSeq seq	 `thenM` \ (new_seq, fvs) ->
     return (PArrSeq noPostTcExpr new_seq, fvs)
+
+rnExpr HsHole
+  = return (HsHole, emptyFVs)
 \end{code}
 
 These three are pattern syntax appearing in expressions.
diff --git a/compiler/typecheck/TcExpr.lhs b/compiler/typecheck/TcExpr.lhs
index 67f212f..b9153ab 100644
--- a/compiler/typecheck/TcExpr.lhs
+++ b/compiler/typecheck/TcExpr.lhs
@@ -215,6 +215,8 @@ tcExpr (HsType ty) _
 	-- so it's not enabled yet.
 	-- Can't eliminate it altogether from the parser, because the
 	-- same parser parses *patterns*.
+tcExpr HsHole _
+  = return HsHole
 \end{code}