runghc shows the value produced by main when its type is a non-() Show instance

When running a program like this:

main :: IO Int
main = return 5

With runghc, it'll print a value, which is contrary to expected behavior and to compiled program behavior:

$ runghc Main.hs
5
$ ghc Main.hs
[1 of 1] Compiling Main             ( Main.hs, Main.o )
Linking Main ...
$ ./Main
$

This is the same as ghci's behavior with an IO action, so presumably runghc is taking a shortcut here. But a program should behave the same way in both cases.

Trac metadata

Trac field	Value
Version	7.8.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture