Hi Oscar, Define result = (.) Then '(result f) g' applies f to the result part of a function g. That's what you want when negating the result of not. For (==), you want to negate the result of the result, so you'd instead say '(result.result) not (==)'. Keep composing result for deeper applications. If you want to edit/transform the first or second part of a pair instead of the result of a function, then you'd use 'first' or 'second' in place of 'result'. If you think of f (here f=not) as an "semantic editor" (transformer) of values, then 'result', 'first', and 'second' are "semantic editor combinators", which can be composed together arbitrarily. See http://conal.net/blog/semantic-editor-combinators . - Conal 2008/12/26 Oscar Picasso <oscarpicasso@gmail.com>
Hi,
I can write: *Main> let yes = not . not *Main> :t yes yes :: Bool -> Bool
But not: *Main> let isNotEqual = not . (==)
<interactive>:1:23: Couldn't match expected type `Bool' against inferred type `a -> Bool' Probable cause: `==' is applied to too few arguments In the second argument of `(.)', namely `(==)' In the expression: not . (==)
Why?
Oscar