The only book I found helpful in learning functional programming was Lambda calculus and combinators by Hindley. Although you can find it online for free it’s w

The only book I found helpful in learning functional programming was Lambda calculus and combinators by Hindley. Although you can find it online for free it’s worth buying. What I discovered was that books on Haskell simply weren’t enough to understand the language, you really do need to understand lambda calculus first.