; What color is your function?
; Impure functions are functions that can call both pure and impure functions.
; Pure functions can only call pure functions.
; Impure function names end in an exclamation mark (!) by convention.
; The top-level context is impure but has special rules
;   related to `import`, `let`, and other builtins.

; this is a pure function
(let f (\[x] x))

(f 10) ; works

; this is an impure function
(let g! (\![x] (println! x)))

(g! "foo") ; works

; this is a pure function that tries to call an impure function
(let h (\[x] (g! x)))

(h "bar")
; error: cannot call impure function in pure context
;   when calling function g! at examples/purity-test.milch:19:15
;   in a function definition at examples/purity-test.milch:19:12
;   when calling function h at examples/purity-test.milch:21:1