[project @ 1999-06-30 11:29:53 by simonmar]

Allow the following (not strictly H98) construct:

    do
	blah
	e $ do
	blah

This doesn't break any existing code, just allows more programs
through.  Only the semantics for layout after a 'do' have changed.

diff --git a/ghc/compiler/parser/Lex.lhs b/ghc/compiler/parser/Lex.lhs
index d705043..efcda1b 100644 (file)
--- a/ghc/compiler/parser/Lex.lhs
+++ b/ghc/compiler/parser/Lex.lhs
@@ -1198,13 +1198,25 @@ h = h
        - we still need to insert another '}' followed by a ';',
          hence the atbol trick.
 
+There's also a special hack in here to deal with
+
+       do
+          ....
+          e $ do
+          blah
+
+i.e. the inner context is at the same indentation level as the outer
+context.  This is strictly illegal according to Haskell 98, but
+there's a lot of existing code using this style and it doesn't make
+any sense to disallow it, since empty 'do' lists don't make sense.
 -}
 
-layoutOn :: P ()
-layoutOn buf s@(PState{ bol = bol, context = ctx }) =
+layoutOn :: Bool -> P ()
+layoutOn strict buf s@(PState{ bol = bol, context = ctx }) =
     let offset = lexemeIndex buf -# bol in
     case ctx of
-       Layout prev_off : _ | prev_off >=# offset ->
+       Layout prev_off : _ 
+          | if strict then prev_off >=# offset else prev_off ># offset ->
                --trace ("layout on, column: " ++  show (I# offset)) $
                POk s{ context = Layout (offset +# 1#) : ctx, atbol = 1# } ()
        other -> 

diff --git a/ghc/compiler/parser/Parser.y b/ghc/compiler/parser/Parser.y
index 3348da9..ef83b5e 100644 (file)
--- a/ghc/compiler/parser/Parser.y
+++ b/ghc/compiler/parser/Parser.y
@@ -1,6 +1,6 @@
 {-
 -----------------------------------------------------------------------------
-$Id: Parser.y,v 1.9 1999/06/28 16:42:23 simonmar Exp $
+$Id: Parser.y,v 1.10 1999/06/30 11:29:53 simonmar Exp $
 
 Haskell grammar.
 
@@ -760,8 +760,8 @@ gdpat       :: { RdrNameGRHS }
 -- Statement sequences
 
 stmtlist :: { [RdrNameStmt] }
-       : '{'            stmts '}'      { reverse $2 }
-       |     layout_on  stmts close    { reverse $2 }
+       : '{'                   stmts '}'       { reverse $2 }
+       |     layout_on_for_do  stmts close     { reverse $2 }
 
 stmts :: { [RdrNameStmt] }
        : ';' stmts1                    { $2 }
@@ -949,7 +949,8 @@ close :: { () }
        : vccurly               { () } -- context popped in lexer.
        | error                 {% popContext }
 
-layout_on  :: { () }   :       {% layoutOn  }
+layout_on        :: { () }     : {% layoutOn True{-strict-} }
+layout_on_for_do  :: { () }    : {% layoutOn False }
 
 -----------------------------------------------------------------------------
 -- Miscellaneous (mostly renamings)