repl attempts to parse type-annotated expressions as type signatures

For example:

```
> bottom :: Int
Error found:
in module $PSCI
at <internal> line 0, column 0 - line 0, column 0

  The type declaration for bottom should be followed by its definition.

> (bottom :: Int)
-2147483648
```

It would be nice if both of these behaved the same way, I think.