bolt/src/test/type-inference.md

Record types can be unified without causing an error

struct Person.
  email: String
  age: Int

let bert = Person { email = "bar@boo.com", age = 32 }
let bob = Person { email = "boo", age = 43 }

bert == bob

Return types are polymorphic

let id x = x

id 1
id "foo"
id True

Nested definitions work

let foo x.
  let bar y z = y + z - x
  bar

foo True

Everything that can be type-checked will be type-checked

let foo n.
  let f : String = 1
  return n

Recursive definitions do not cause infinite loops in the type-checker

let fac n = fac_2 n

let fac_2 n = fac_3 n + fac n

let fac_3 n = fac_2 (n-1)

not (fac 1)

Example with mutual recursion works

let is_even x.
  if x == 0.
    return True
  else.
    return is_odd (x-1)

let is_odd x.
  if x == 1.
    return False
  else.
    return is_even (x-1)

not (is_even True)