GHC infers over-general types
Consider
f x = x + headGHC will (with no flags) will compile this almost-certainly-wrong program, giving f the type
f :: forall a. Num ([a] -> a) => ([a] -> a) -> [a] -> aThere's nothing wrong with that type, and in principle someone might later define a suitable instance of Num, but (a) it's not Haskell 98, and (b) it's unlikely to be right, so we've deferred a type error from the definition site of f to the (perhaps much later) call site.
I think GHC should complain, and require a type signature if that's what you really want. This came up on Stackoverflow
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.4.1 |
| Type | Bug |
| TypeOfFailure | OtherFailure |
| Priority | high |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |