Fix Trac #3813: unused variables in GHCi bindings

[ghc-hetmet.git] / compiler / rename / RnPat.lhs

diff --git a/compiler/rename/RnPat.lhs b/compiler/rename/RnPat.lhs
index 6367255..c06aa38 100644 (file)
--- a/compiler/rename/RnPat.lhs
+++ b/compiler/rename/RnPat.lhs
@@ -133,9 +133,11 @@ which is how you go from a RdrName to a Name
 data NameMaker 
   = LamMk      -- Lambdas 
       Bool     -- True <=> report unused bindings
+               --   (even if True, the warning only comes out 
+               --    if -fwarn-unused-matches is on)
 
   | LetMk       -- Let bindings, incl top level
-               -- Do not check for unused bindings
+               -- Do *not* check for unused bindings
       (Maybe Module)   -- Just m  => top level of module m
                        -- Nothing => not top level
       MiniFixityEnv
@@ -146,8 +148,14 @@ topRecNameMaker mod fix_env = LetMk (Just mod) fix_env
 localRecNameMaker :: MiniFixityEnv -> NameMaker
 localRecNameMaker fix_env = LetMk Nothing fix_env 
 
-matchNameMaker :: NameMaker
-matchNameMaker = LamMk True
+matchNameMaker :: HsMatchContext a -> NameMaker
+matchNameMaker ctxt = LamMk report_unused
+  where
+    -- Do not report unused names in interactive contexts
+    -- i.e. when you type 'x <- e' at the GHCi prompt
+    report_unused = case ctxt of
+                      StmtCtxt GhciStmt -> False
+                      _                 -> True
 
 newName :: NameMaker -> Located RdrName -> CpsRn Name
 newName (LamMk report_unused) rdr_name
@@ -212,8 +220,8 @@ rnPats ctxt pats thing_inside
          -- (0) bring into scope all of the type variables bound by the patterns
          -- (1) rename the patterns, bringing into scope all of the term variables
          -- (2) then do the thing inside.
-       ; bindPatSigTyVarsFV (collectSigTysFromPats pats) $ 
-         unCpsRn (rnLPatsAndThen matchNameMaker pats)    $ \ pats' -> do
+       ; bindPatSigTyVarsFV (collectSigTysFromPats pats)     $ 
+         unCpsRn (rnLPatsAndThen (matchNameMaker ctxt) pats) $ \ pats' -> do
         { -- Check for duplicated and shadowed names 
                 -- Because we don't bind the vars all at once, we can't
                 --     check incrementally for duplicates;