The way I first learned to think functionally was reading and working through http://realmofracket.com/ http://realmofracket.com/ It intros you to Racket, which

The way I first learned to think functionally was reading and working through http://realmofracket.com/ http://realmofracket.com/ It intros you to Racket, which is sort of a Scheme dialect (which is a Lisp dialect) and teaches functional programming. Haskell, OCaml, etc take those functional idioms and apply strong typing, algebraic data types, pattern matching and something like the Option/Maybe type - but they build on the same functional concepts in Realm of Racket. Caveats to the above: 1) Racket has an optional 'typed' variant which gives you type checking. 2) Rust is (IMHO) a little weaker with regards to pure functional programming than OCaml, but very nicely integrates pattern matching, type checking and algebraic data types in.