Il 23 dicembre 2020 alle 21:12 Lawrence Bottorff ha scritto:
I have these three versions of addition
addA x y = x + y addB x = \y -> x + y addC = \x -> \y -> x + y
[…]
I can't see how addB and addC are actually accomplishing this. addA is currying, which I don't fully follow.
Parameters on the left-hand side of a function definition can always be expressed as a lambda, by «plucking» them from the rightmost one addA x y = x + y addA x = \y -> x + y addA = \x -> \y -> x + y -- those three are equal! Intuitively you can say that first we are binding the patterns in the function definition and then the one left in the lambda right-hand side (if any). So: add 3 5 addA x = \y -> x + y 3 5 \y -> 3 + y 5 3 + 5 I suspect what the book is trying to teach you is that you can partially apply a function and pass it around merrily: map (addA 3) [1, 2, 3] So by writing `addA 3` we obtain: addA :: Int -> Int -> Int addA :: Int -> (Int -> Int) -- can also be written like this -- since `(->)` is associates to -- the right add3 :: Int -> Int -- applying addA to 3 another function with one parameter less. Once everything is applied, you will get your result!