Comments only; record remarks about removing 'type' nonterminal

diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp
index 8806a3d..b73deb5 100644 (file)
--- a/compiler/parser/Parser.y.pp
+++ b/compiler/parser/Parser.y.pp
@@ -1004,6 +1004,17 @@ strict_mark :: { Located HsBang }
        : '!'                           { L1 HsStrict }
        | '{-# UNPACK' '#-}' '!'        { LL HsUnbox }
 
        : '!'                           { L1 HsStrict }
        | '{-# UNPACK' '#-}' '!'        { LL HsUnbox }
 

+----------------------
+-- Notes for 'ctype'
+-- We should probably use 'gentype' rather than 'type' in the LHS of type declarations
+-- That would leave the only use of 'type' in 'ctype'; and only one of its occurrences 
+-- makes sense there too! So it might make sense to inline type there:
+--    ctype : 'forall' tv_bndrs '.' ctype
+--          | context '=>' ctype           
+--          | ipvar '::' gentype
+--          | gentype
+-- Which in turn would let us rename gentype to type 
+

 -- A ctype is a for-all type
 ctype  :: { LHsType RdrName }
        : 'forall' tv_bndrs '.' ctype   { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }
 -- A ctype is a for-all type
 ctype  :: { LHsType RdrName }
        : 'forall' tv_bndrs '.' ctype   { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }

@@ -1011,32 +1022,47 @@ ctype   :: { LHsType RdrName }
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | type                          { $1 }
 
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | type                          { $1 }
 

+type :: { LHsType RdrName }
+       : ipvar '::' gentype            { LL (HsPredTy (HsIParam (unLoc $1) $3)) }
+       | gentype                       { $1 }
+
+----------------------
+-- Notes for 'ctypedoc'
+-- It would have been nice to simplify the grammar by unifying `ctype` and 
+-- ctypedoc` into one production, allowing comments on types everywhere (and
+-- rejecting them after parsing, where necessary).  This is however not possible
+-- since it leads to ambiguity. The reason is the support for comments on record
+-- fields: 
+--         data R = R { field :: Int -- ^ comment on the field }
+-- If we allow comments on types here, it's not clear if the comment applies
+-- to 'field' or to 'Int'. So we must use `ctype` to describe the type.
+

 ctypedoc :: { LHsType RdrName }
        : 'forall' tv_bndrs '.' ctypedoc        { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }
        | context '=>' ctypedoc         { LL $ mkImplicitHsForAllTy   $1 $3 }
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | typedoc                               { $1 }
 
 ctypedoc :: { LHsType RdrName }
        : 'forall' tv_bndrs '.' ctypedoc        { LL $ mkExplicitHsForAllTy $2 (noLoc []) $4 }
        | context '=>' ctypedoc         { LL $ mkImplicitHsForAllTy   $1 $3 }
        -- A type of form (context => type) is an *implicit* HsForAllTy
        | typedoc                               { $1 }
 

+typedoc :: { LHsType RdrName }
+       : ipvar '::' gentype            { LL (HsPredTy (HsIParam (unLoc $1) $3)) }
+       | gentypedoc                    { $1 }
+
+----------------------
+-- Notes for 'context'

 -- We parse a context as a btype so that we don't get reduce/reduce
 -- errors in ctype.  The basic problem is that
 --     (Eq a, Ord a)
 -- looks so much like a tuple type.  We can't tell until we find the =>
 -- We parse a context as a btype so that we don't get reduce/reduce
 -- errors in ctype.  The basic problem is that
 --     (Eq a, Ord a)
 -- looks so much like a tuple type.  We can't tell until we find the =>

---
--- We have the t1 ~ t2 form here and in gentype, to permit an individual
--- equational constraint without parenthesis.
+
+-- We have the t1 ~ t2 form both in 'context' and in gentype, 
+-- to permit an individual equational constraint without parenthesis.
+-- Thus for some reason we allow    f :: a~b => blah
+-- but not                         f :: ?x::Int => blah

 context :: { LHsContext RdrName }
         : btype '~'      btype         {% checkContext
                                             (LL $ HsPredTy (HsEqualP $1 $3)) }
        | btype                         {% checkContext $1 }
 
 context :: { LHsContext RdrName }
         : btype '~'      btype         {% checkContext
                                             (LL $ HsPredTy (HsEqualP $1 $3)) }
        | btype                         {% checkContext $1 }
 

-type :: { LHsType RdrName }
-       : ipvar '::' gentype            { LL (HsPredTy (HsIParam (unLoc $1) $3)) }
-       | gentype                       { $1 }
-
-typedoc :: { LHsType RdrName }
-       : ipvar '::' gentype            { LL (HsPredTy (HsIParam (unLoc $1) $3)) }
-       | gentypedoc                    { $1 }
-

 gentype :: { LHsType RdrName }
         : btype                         { $1 }
         | btype qtyconop gentype        { LL $ HsOpTy $1 $2 $3 }
 gentype :: { LHsType RdrName }
         : btype                         { $1 }
         | btype qtyconop gentype        { LL $ HsOpTy $1 $2 $3 }