diff options
| -rw-r--r-- | compiler/parser/Parser.y.pp | 48 |
1 files changed, 37 insertions, 11 deletions
diff --git a/compiler/parser/Parser.y.pp b/compiler/parser/Parser.y.pp index 8806a3d4ef..b73deb534a 100644 --- 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 } +---------------------- +-- 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 } @@ -1011,32 +1022,47 @@ ctype :: { LHsType RdrName } -- 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 } +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 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 } -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 } |