Question

I have the function pyths:

-- takes an Int and returns a list of pythagorean triples whose components 
---- are at most the given Int
pyths :: Int a => a -> [(Int, Int, Int)]
pyths n = [(x, y, z) | x <- f, y <- f, z <- f, x^2 + y^2 == z^2] 
  where f = factors n

I get the error that factors is out of scope. How can I write this function so it’s in scope?

I’ve tried:

pyths n = [(x, y, z) | x <- f, y <- f, z <- f, x^2 + y^2 == z^2 where f = factors n]

and:

pyths n = [(x, y, z) | x <- f, y <- f, z <- f, x^2 + y^2 == z^2, where f = factors n]

But then I just get syntax errors.

---

Note:
I know this may not actually do what I intend it to do.

Answer 1

As sepp2k said, you need to define factors. In your examples you change where f is defined, which uses factors in its definition, but no where do you say:

factors x = ...

Since there is no factors function defined in the Haskell prelude or other base libraries, you must write this yourself. The primes package will be useful to you, I expect.