A brainfuck interpreter written using mostly lambdas, helped along by the Church gem.

brainfuck_church.rb

require 'church'
include  Church

brainfuck = -> prog {
  tape = []
  sz = SIZE[prog]
  pc = bp = i = 0
  jumps, stack = {}, []
 
  (jumper = -> {
    prog[i] == '[' ? (stack << i) : 0
    prog[i] == ']' ? (jumps[stack[-1]] = i; stack = stack[0..-2]) : 0
    (i += 1) == sz ? 0 : jumper[]
  })[]
 
  jumps = jumps == {} ? {} : MERGE[jumps, INVERT[jumps]]
 
  (brainfuck_p = -> {
    prog[pc] ==
    '+' ? (tape[bp] ||= 0; tape[bp] += 1) : prog[pc] ==
    '-' ? (tape[bp] ||= 0; tape[bp] -= 1) : prog[pc] ==
    '>' ? (bp += 1) : prog[pc] ==
    '<' ? (bp -= 1) : prog[pc] ==
    '[' ? (pc = (tape[bp] || 0) == 0 ? jumps[pc] : pc) : prog[pc] ==
    ']' ? (pc = (tape[bp] || 0) != 0 ? jumps[pc] : pc) : prog[pc] ==
    '.' ? ($> << ('' << tape[bp])) : 0
 
    (pc += 1) == sz ? prog : brainfuck_p[]
  })[]
}