Hi,
:t 42 42 :: Num t => t
The parser has to make some choices to distinguish between negate and subtraction. In ambiguous cases, subtraction is chosen:
abs -42
<interactive>:2:1: error: • Non type-variable argument in the constraint: Num (a -> a) (Use FlexibleContexts to permit this) • When checking the inferred type it :: forall a. (Num (a -> a), Num a) => a -> a
abs (-42) 42 let abs=10 abs-42 -32 abs -42 -32 abs - 42 -32 abs (-42)
<interactive>:15:1: error: • Non type-variable argument in the constraint: Num (t -> t1) (Use FlexibleContexts to permit this) • When checking the inferred type it :: forall t t1. (Num (t -> t1), Num t) => t1 It leads to some confusion:
fmap (+ 42) [1,2] [43,44] fmap (- 42) [1,2]
<interactive>:12:1: error: • Non type-variable argument in the constraint: Num (a -> b) (Use FlexibleContexts to permit this) • When checking the inferred type it :: forall a b. (Num (a -> b), Num a) => [b]
fmap (flip (-) 42) [1,2] [-41,-40]
Cheers Sylvain On 24/09/2016 15:54, Olumide wrote:
Is 42 a function? And if it is why does 42 + 24 work, if both are functions. I know there's something I'm getting wrong here.
Also, is the expression abs -42 an error. I initially thought that abs to the operator (-) first but there is no space between - and 42. Or is there some associativity issue going on here.
- Olumide _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners