On Sat, Apr 01, 2006 at 01:50:54PM +0100, Brian Hulley wrote:
Greg Buchholz wrote:
f x = x + 2 g x = x + 1 + 1
Interesting! Referential transparency (as I understand it) has indeed been violated. Perhaps the interaction of GADTs and type classes was not sufficiently studied before being introduced to the language.
You cal also tell them apart with some built-in Haskell types, try: (f 1e16 :: Double) == g 1e16 You automatically assume that Num operations have some additional properties, but it's not always true. When +, fromIntegral are unknown, you can't be sure that 1 + 1 is the same as 2. I think it is still meaningful to talk about referential transparency if you treat all functions like + and fromIntegral as black boxes. For example, in many programming languages it's not true that let y = f x in (y, y) is the same as (f x, f x) Best regards Tomasz