Kitten

A Concatenative language by Jon Purdy with static typing, type inference, and effect types. Not actively developed since 2018.

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Example

define fib_naive (UInt64 -> UInt64):
  -> n;
  if (n <= 1u64):
    1u64
  else:
    (n - 2u64) fib_naive + (n - 1u64) fib_naive

define fib_tailrec (UInt64 -> UInt64):
  1u64 1u64 fib_tailrec_helper

define fib_tailrec_helper (UInt64, UInt64, UInt64 -> UInt64):
  -> n, a, b;
  if (n = 0u64):
    a
  elif (n = 1u64):
    b
  else:
    (n - 1u64) b (a + b) fib_tailrec_helper

define fib_fix (UInt64 -> UInt64):
  do (fix) -> n, rec:
    if (n <= 1u64):
      1u64
    else:
      (n - 2u64) rec call -> a;
      (n - 1u64) rec call -> b;
      a + b

define test ((UInt64 -> UInt64) -> +IO):
  10u64 swap call say

[\fib_naive, \fib_tailrec, \fib_fix] \test each