Type inference interferes with referential transparency

Question

What is the precise promise/guarantee the Haskell language provides with respect to referential transparency? At least the Haskell report does not mention this notion.

C

Answer 1

Probably another type-inference and referential-transparency related thing is the „dreaded“ Monomorphism restriction (its absence, to be exact). A direct quote:

An example, from „A History of Haskell“:
Consider the genericLength function, from Data.List

genericLength :: Num a => [b] -> a

And consider the function:

f xs = (len, len) where len = genericLength xs

len has type Num a => a and, without the monomorphism restriction, it could be computed twice.

Notice that in this case types of both expressions are the same. Results are too, but the substitution isn't always possible.