code-conjure-0.7.6: eg/factorial.hs

-- factorial.hs: conjuring a factorial function
--
-- Copyright (C) 2021-2025 Rudy Matela
-- Distributed under the 3-Clause BSD licence (see the file LICENSE).
import Conjure

factorial :: Int -> Int
factorial 1  =  1
factorial 2  =  2
factorial 3  =  6
factorial 4  =  24


main :: IO ()
main  =  do
  -- explicit recursion
  conjure "factorial n" factorial
    [ con (0::Int)
    , con (1::Int)
    , fun "+" ((+) :: Int -> Int -> Int)
    , fun "*" ((*) :: Int -> Int -> Int)
    , fun "-" ((-) :: Int -> Int -> Int)
    ]
  -- should produce:
  -- factorial 0  =  1
  -- factorial x  =  x * factorial (x - 1)

  -- using foldr and enumFromTo
  conjure "factorial n" factorial
    [ con (0::Int)
    , con (1::Int)
    , fun "+" ((+) :: Int -> Int -> Int)
    , fun "*" ((*) :: Int -> Int -> Int)
    , fun "-" ((-) :: Int -> Int -> Int)
    , fun ".." (enumFromTo :: Int -> Int -> [Int])
    , fun "foldr" (foldr :: (Int -> Int -> Int) -> Int -> [Int] -> Int)
    ]
  -- should produce:
  -- factorial x  =  foldr (*) 1 [1..x]