[project @ 1997-05-19 06:25:00 by sof]

[ghc-hetmet.git] / ghc / compiler / basicTypes / FieldLabel.lhs

diff --git a/ghc/compiler/basicTypes/FieldLabel.lhs b/ghc/compiler/basicTypes/FieldLabel.lhs
index 0173833..7eea7b8 100644 (file)
--- a/ghc/compiler/basicTypes/FieldLabel.lhs
+++ b/ghc/compiler/basicTypes/FieldLabel.lhs
@@ -19,9 +19,16 @@ import UniqFM           ( SYN_IE(Uniquable) )
 
 \begin{code}
 data FieldLabel
-  = FieldLabel Name            -- Also used as the Name of the field selector Id
-               Type
-               FieldLabelTag
+  = FieldLabel Name            -- Also used as the Name of the field selector Id
+               Type            -- Type of the field; may have free type variables that
+                               -- are the tyvar of the constructor
+                               -- e.g.  data T a = MkT { op1 :: a -> a, op2 :: a -> Int }
+                               -- The type in the FieldLabel for op1 will be simply (a->a).
+
+               FieldLabelTag   -- Indicates position within constructor
+                               -- If the same field occurs in more than one constructor
+                               -- then it'll have a separate FieldLabel on each occasion,
+                               -- but with a single name (and presumably the same type!)
 
 type FieldLabelTag = Int