[project @ 2000-11-28 11:38:35 by simonpj]

Trim example

diff --git a/ghc/tests/typecheck/should_compile/tc110.hs b/ghc/tests/typecheck/should_compile/tc110.hs
index 9f9fa24..1422d89 100644 (file)
--- a/ghc/tests/typecheck/should_compile/tc110.hs
+++ b/ghc/tests/typecheck/should_compile/tc110.hs
@@ -8,28 +8,15 @@ module ShouldCompile where
 -- Reported by Thomas Hallgren Nov 00
 
 
-foo = dup 1 >>= print
+primDup :: Int -> IO Int
+primDup = undefined
 
-foreign import "dup" primDup :: Int -> IO Int
---dup :: Int -> IO Int               -- not needed with (1), needed with (2)
-dup = call primDup                   -- ghc crashes here with (1), ok with (2)
+dup () = call primDup
 
-class Call    c h | c -> h where call  :: c -> h            -- (1) problematic
---class Call    c h          where call  :: c -> h          -- (2) ok
+class Call    c h | c -> h where
+    call  :: c -> h
 
-class Result  c h | c -> h where fromC :: c -> IO h
+instance Call c h => Call (Int->c) (Int->h) where 
+    call f = call . f
 
-instance Result c h => Call (IO c) (IO h) where call f = fromC =<< f
-instance Call c h => Call (Int->c) (Int->h) where call f = call . f
 
-instance Result Int Int where fromC = return
-
-
-{-
-The example is perhaps too stripped down to illustrate the purpose of these
-classes, but the idea is that the class "Call" should relate suitably declared
-low-level prim_types in foreign imports to sensible, high-level Haskell types,
-allowing high level functions to be obtained by simply applying the method
-"call" to the primitive function, as in the definition of dup above, without
-having to explicitly give also the type of the high level function.
--}