[commit: ghc] master: Comments only (ef391f8)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/ef391f88ecde6d66cae0fd216ba0d25956fec1fb/ghc

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

commit ef391f88ecde6d66cae0fd216ba0d25956fec1fb
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Thu Feb 19 20:53:55 2015 +0000

    Comments only


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

ef391f88ecde6d66cae0fd216ba0d25956fec1fb
 compiler/typecheck/TcBinds.hs |  2 +-
 compiler/typecheck/TcPat.hs   | 37 +++++++++++++++++++++----------------
 2 files changed, 22 insertions(+), 17 deletions(-)

diff --git a/compiler/typecheck/TcBinds.hs b/compiler/typecheck/TcBinds.hs
index acdaf8f..7b988da 100644
--- a/compiler/typecheck/TcBinds.hs
+++ b/compiler/typecheck/TcBinds.hs
@@ -542,7 +542,7 @@ tcPolyCheck :: RecFlag       -- Whether it's recursive after breaking
             -> TcM (LHsBinds TcId, [TcId], TopLevelFlag)
 -- There is just one binding,
 --   it binds a single variable,
---   it has a signature,
+--   it has a complete type signature,
 tcPolyCheck rec_tc prag_fn
             sig@(TcSigInfo { sig_name = name, sig_poly_id = Just poly_id
                            , sig_tvs = tvs_w_scoped
diff --git a/compiler/typecheck/TcPat.hs b/compiler/typecheck/TcPat.hs
index 7856413..9f37a56 100644
--- a/compiler/typecheck/TcPat.hs
+++ b/compiler/typecheck/TcPat.hs
@@ -140,12 +140,16 @@ data TcSigInfo
                               -- sig_id = Just id, then sig_name = idName id.
 
         sig_poly_id :: Maybe TcId,
-                              -- Just <=> complete type signature of
-                              -- which the polymorphic type is known.
-                              -- Nothing <=> partial type signature of
-                              -- which the type is not yet fully
-                              -- known.
-                              -- See Note [Complete and partial type signatures]
+             -- Just f <=> the type signature had no wildcards, so the precise, 
+             --            complete polymorphic type is known.  In that case,
+             --            f is the polymorphic Id, with that type
+           
+             -- Nothing <=> the type signature is partial (i.e. includes one or more
+             --             wildcards). In this case it doesn't make sense to give
+             --             the polymorphic Id, because we are going to /infer/ its
+             --             type, so we can't make the polymorphic Id ab-initio
+             --
+             -- See Note [Complete and partial type signatures]
 
         sig_tvs    :: [(Maybe Name, TcTyVar)],
                            -- Instantiated type and kind variables
@@ -154,16 +158,17 @@ data TcSigInfo
 
         sig_nwcs   :: [(Name, TcTyVar)],
                            -- Instantiated wildcard variables
+                           -- If sig_poly_id = Just f, then sig_nwcs must be empty
 
-        sig_theta  :: TcThetaType,  -- Instantiated theta
-
-        sig_extra_cts :: Maybe SrcSpan, -- Just loc <=> An extra-constraints
-                                        -- wildcard was present. Any extra
-                                        -- constraints inferred during
-                                        -- type-checking will be added to the
-                                        -- partial type signature. Stores the
-                                        -- location of the wildcard.
+        sig_extra_cts :: Maybe SrcSpan, 
+                           -- Just loc <=> An extra-constraints wildcard was present
+                           --              at location loc
+                           --   e.g.   f :: (Eq a, _) => a -> a
+                           -- Any extra constraints inferred during
+                           -- type-checking will be added to the sig_theta.
+                           -- If sig_poly_id = Just f, sig_extra_cts must be Nothing
 
+        sig_theta  :: TcThetaType,  -- Instantiated theta
         sig_tau    :: TcSigmaType,  -- Instantiated tau
                                     -- See Note [sig_tau may be polymorphic]
 
@@ -288,8 +293,8 @@ res_ty free vars.
 
 Note [Complete and partial type signatures]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-A type signature is partial when it contains one or more wildcards.
-The wildcard can either be:
+A type signature is partial when it contains one or more wildcards
+(= type holes).  The wildcard can either be:
 * A (type) wildcard occurring in sig_theta or sig_tau. These are
   stored in sig_nwcs.
       f :: Bool -> _