:info (->) doesn't print all relevant instances

I noticed that ":info (->)" does not does not print all relevant instances, specifically instances whose heads use -> in an infix way. For example,

$ ghci -v0
Prelude> import Data.Monoid
Prelude Data.Monoid> :i (->)
data (->) a b   -- Defined in `GHC.Prim'
instance Monad ((->) r) -- Defined in `GHC.Base'
instance Functor ((->) r) -- Defined in `GHC.Base'
Prelude Data.Monoid>

The instance Monoid b => Monoid (a -> b) is not printed.

Trac metadata

Trac field	Value
Version	7.6.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	GHCi
Test case
Differential revisions
BlockedBy
Related
Blocking
CC	hvr
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changed weight to 5

added GHCi Tbug Trac import labels

Here's a validated diff that fixes this issue:

diff --git a/compiler/typecheck/TcType.lhs b/compiler/typecheck/TcType.lhs
index 9ccb08a..430dfb0 100644
--- a/compiler/typecheck/TcType.lhs
+++ b/compiler/typecheck/TcType.lhs
@@ -1316,7 +1316,9 @@ orphNamesOfType (TyVarTy _)                = emptyNameSet
 orphNamesOfType (TyConApp tycon tys)       = orphNamesOfTyCon tycon
                                              `unionNameSets` orphNamesOfTypes tys
 orphNamesOfType (LitTy {})          = emptyNameSet
-orphNamesOfType (FunTy arg res)     = orphNamesOfType arg `unionNameSets` orphNamesOfType res
+orphNamesOfType (FunTy arg res)     = orphNamesOfTyCon funTyCon `unionNameSets`
+                                        orphNamesOfType arg `unionNameSets`
+                                        orphNamesOfType res
 orphNamesOfType (AppTy fun arg)     = orphNamesOfType fun `unionNameSets` orphNamesOfType arg
 orphNamesOfType (ForAllTy _ ty)     = orphNamesOfType ty

I am not sure how this diff affects the other callers (aside from the ":info" machinery, that is) of orphNamesOfType. It passes validation, at least.

Great point. I'll commit this.

Simon

mentioned in commit 26c9d591

mentioned in commit cb9a3b38

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed
Test case	→ ghci/scripts/T8535

added Pnormal label