Question

Let’s say I have a function a that takes one argument, and a list b with possible inputs, defined as:

let a x1 = x1 == 3
let b = [3, 3]

Now I want to test that all values in b returns True as arguments to a, which I can do with the all function:

all a b
> True

However, can I do something similar if a would take two arguments and b would be a list of tuples where each value in the tuple correspond to each argument?

E.g.:

let a x1 x2 = x1 == 3 && x2 == 1
let b = [(3,1), (3,1)]
all a b

This returns:

<interactive>:1:4:
    Couldn't match expected type `Bool'
           against inferred type `a1 -> Bool'
    In the first argument of `all', namely `a'
    In the expression: all a b
    In the definition of `it': it = all a b

Any ideas on how to do this?

Answer 1

To turn a function with two arguments into a function expecting one pair, use

uncurry :: (r -> s -> t) -> (r, s) -> t

So, how about

all (uncurry a) b

?