hylogen 1.4

findwithdefault.hs

import Hylogen.Expr
import Hylogen.WithHylide

findWithDefault :: ToGLSLType a =>
                   (Expr a -> Booly) -> Expr a ->  [Expr a] -> Expr a
findWithDefault predicate = foldr (\x acc -> sel (predicate x) x acc)


findWithDefault' :: (ToGLSLType a, ToGLSLType b) =>
                    (Expr a -> Booly) -> Expr b ->  [(Expr a, Expr b)] -> Expr b
findWithDefault' predicate x = foldr (\(a, b) acc -> sel (predicate a) b acc) x


foo :: Vec1
foo = findWithDefault (`lt`10) 0 [1, 2, 11, 12, 14]
-- ( (true && (1.0 < 10.0)) ? 1.0 : ( (true && (2.0 < 10.0)) ? 2.0 : ( (true && (11.0 < 10.0)) ? 11.0 : ( (true && (12.0 < 10.0)) ? 12.0 : ( (true && (14.0 < 10.0)) ? 14.0 : 0.0)))))

bar :: Vec1
bar = findWithDefault' (`gt` time) 0 [(0, 0), (100, 1)]
-- ( (true && (0.0 > time)) ? 0.0 : ( (true && (100.0 > time)) ? 1.0 : 0.0))

Here are the functions with explicit recursion:

Keep in mind sel is just the ternary operator:

-- haskell
sel b x y

-- C, javascript
b ? x : y

If x matches by the predicate, sel branches to x. Else, it recurses down the list.

findWithDefault predicate def (x:xs) = sel (predicate x) x (findWithDefault predicate def xs)
findWithDefault predicate def [] = def

Given (a, b) from the list, if a matches by the predicate, sel branches to b. Else, it recurses down the list.

findWithDefault' predicate def ((a, b):xs) = sel (predicate a) b (findWithDefault predicate def xs)
findWithDefault' predicate def [] = def