[project @ 2000-03-23 17:45:17 by simonpj]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcRules.lhs

diff --git a/ghc/compiler/typecheck/TcRules.lhs b/ghc/compiler/typecheck/TcRules.lhs
index 53fc649..c5cdf0c 100644 (file)
--- a/ghc/compiler/typecheck/TcRules.lhs
+++ b/ghc/compiler/typecheck/TcRules.lhs
@@ -72,6 +72,17 @@ tcRule (RuleDecl name sig_tvs vars lhs rhs src_loc)
        -- Gather the template variables and tyvars
     let
        tpl_ids = map instToId (bagToList lhs_dicts) ++ ids
+
+       -- IMPORTANT!  We *quantify* over any dicts that appear in the LHS
+       -- Reason: 
+       --      a) The particular dictionary isn't important, because its value
+       --         depends only on the type
+       --              e.g     gcd Int $fIntegralInt
+       --         Here we'd like to match against (gcd Int any_d) for any 'any_d'
+       --
+       --      b) We'd like to make available the dictionaries bound 
+       --         on the LHS in the RHS, so quantifying over them is good
+       --         See the 'lhs_dicts' in tcSimplifyAndCheck for the RHS
     in
 
        -- Gather type variables to quantify over