T2688

testsuite/tests/ghc-regress/typecheck/should_fail/T2688.hs

+{-# OPTIONS_GHC -XFunctionalDependencies -XMultiParamTypeClasses #-}
+
+module T2688 where
+
+class VectorSpace v s | v -> s where
+    (*^)    :: s -> v -> v
+    (^/)    :: v -> s -> v
+    v ^/ s = v *^ (1/s)

testsuite/tests/ghc-regress/typecheck/should_fail/T2688.stderr

+
+T2688.hs:1:0:
+    Couldn't match expected type `s' against inferred type `v'
+      `s' is a rigid type variable bound by
+          the class declaration for `VectorSpace' at T2688.hs:5:20
+      `v' is a rigid type variable bound by
+          the class declaration for `VectorSpace' at T2688.hs:5:18
+    When using functional dependencies to combine
+      VectorSpace v v, arising from a use of `*^' at T2688.hs:8:13-22
+      VectorSpace v s,
+        arising from the class declaration for `VectorSpace'
+                     at T2688.hs:(5,0)-(8,22)
+
+T2688.hs:8:13:
+    Could not deduce (VectorSpace v v)
+      from the context (VectorSpace v s)
+      arising from a use of `*^' at T2688.hs:8:13-22
+    Possible fix:
+      add (VectorSpace v v) to the context of
+        the class declaration for `VectorSpace'
+    In the expression: v *^ (1 / s)
+    In the definition of `^/': v ^/ s = v *^ (1 / s)
+
+T2688.hs:8:13:
+    Couldn't match expected type `v' against inferred type `s'
+      `v' is a rigid type variable bound by
+          the class declaration for `VectorSpace' at T2688.hs:5:18
+      `s' is a rigid type variable bound by
+          the class declaration for `VectorSpace' at T2688.hs:5:20
+    In the expression: v *^ (1 / s)
+    In the definition of `^/': v ^/ s = v *^ (1 / s)
+
+T2688.hs:8:19:
+    Could not deduce (Fractional v) from the context (VectorSpace v s)
+      arising from a use of `/' at T2688.hs:8:19-21
+    Possible fix:
+      add (Fractional v) to the context of
+        the class declaration for `VectorSpace'
+    In the second argument of `(*^)', namely `(1 / s)'
+    In the expression: v *^ (1 / s)
+    In the definition of `^/': v ^/ s = v *^ (1 / s)

testsuite/tests/ghc-regress/typecheck/should_fail/all.T

@@ -198,3 +198,4 @@ test('T2126', normal, compile_fail, [''])
 test('T2307', normal, compile_fail, [''])
 test('T2414', normal, compile_fail, [''])
 test('T2538', normal, compile_fail, [''])
+test('T2688', normal, compile_fail, [''])