On Thu, Dec 27, 2012 at 8:26 PM, Kim-Ee Yeoh
Hi David, it looks like Rustom's aware that haskell's not lisp. What he really wants methinks is a way to suppress type classes altogether! That or a NoOverloadedNumerals extension.
-- Kim-Ee
I'm not really sure about that... Look! ghci with default startup -------------------- $ ghci GHCi, version 7.4.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :t [[1,2],3] [[1,2],3] :: (Num [t], Num t) => [[t]] So it would appear that ghci is giving a well-typing for [[1,2], 3]. But is it? Prelude> [[1,2],3] <interactive>:3:8: No instance for (Num [t0]) arising from the literal `3' Possible fix: add an instance declaration for (Num [t0]) In the expression: 3 In the expression: [[1, 2], 3] In an equation for `it': it = [[1, 2], 3] ------------------- So is it well-typed in ghci or not?? And now we add Roman's suggestions... $ cat .ghci :set -XRebindableSyntax let fromInteger = id And run ghci again $ ghci GHCi, version 7.4.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :t [[1,2],3] <interactive>:1:8: Couldn't match expected type `[Integer]' with actual type `Integer' Expected type: Integer -> [Integer] Actual type: Integer -> Integer In the expression: 3 In the expression: [[1, 2], 3] Prelude> [[1,2],3] <interactive>:3:8: Couldn't match expected type `[Integer]' with actual type `Integer' Expected type: Integer -> [Integer] Actual type: Integer -> Integer In the expression: 3 In the expression: [[1, 2], 3] Prelude> So far so good -- when an expression is type-wrong, its 'wrongness' is the same irrespective of whether I ask for its type or evaluate it. But now we are in for new surprises: Try out f x y = x / y Prelude> :l f [1 of 1] Compiling Main ( f.hs, interpreted ) f.hs:1:11: Not in scope: `/' Failed, modules loaded: none. Prelude> (/) Oh is it that now integer literals are just plain Integers and cant be divided using '/' ?? So lets replace '/' with '+' f.hs:1:11: Not in scope: `+' And now I am at my wits end!