I'm working through a Haskell book. It has the following example:
ghci> Right 3 >>= \x -> return (x + 100)
It expects that this blows up with this error:
<interactive>:1:0:
Ambiguous type variable `a' in the constraints:
`Error a' arising from a use of `it' at <interactive>:1:0-33
`Show a' arising from a use of `print' at <interactive>:1:0-33
Probable fix: add a type signature that fixes these type variable(s)
When I run it:
$ ghci
Prelude> Right 3 >>= \x -> return (x + 100)
I get:
Right 103
ie I don't get the error expected.
Now maybe the compiler or the library has changed - but I'm not sure how to verify that.
My question is: Why doesn't ghci provide the expected Ambiguous type variable error in this scenario?
Error
having been used in GHCi. Anyone know the history behind this? – Alec