Minimum

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Minimum is a joke language by Ihope127 which is functional and has Unlambda-like syntax. Unlike Unlambda, a Minimum program defines a function which takes the two essential primitive functions, s and k (in that order), and uses them to construct something useful, instead of actually allowing s and k to be specified directly in the program. Though Minimum has an apply operator (Unlambda's `), it has no primitive combinators, therefore making it impossible to program in. The syntax:

<program> ::= "`" <program> <program>

Interpreter

As a functional language, it is especially suiting for an interpreter to be written in Haskell:

{-# LANGUAGE OverloadedStrings #-}

import Data.Attoparsec.ByteString
import Data.Void
import System.Exit (die)
import qualified Data.ByteString as B

data Program = App Program Program

eval :: Program -> Void
eval (App x y) = app (eval x) (eval y)
  where app = absurd

parser :: Parser Program
parser = string "`" *> (App <$> parser <*> parser)

main :: IO ()
main = do
  code <- B.getContents
  case parseOnly parser code of
    Left _ -> die "Invalid program."
    Right program -> absurd (eval program) (\x y z -> x z (y z)) const