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Ever heard of an esoteric language named COW or wanted to run a program written with just the letters M and O? This recipe provides a COW interpreter that is able to run such programs and decodes them so that they are much easier to read for those who do not know the common bovine tongue.

Python, 247 lines
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INS = ['moo', 'mOo', 'moO', 'mOO', 'Moo', 'MOo',
       'MoO', 'MOO', 'OOO', 'MMM', 'OOM', 'oom']

HLP = dict((s, i) for i, s in enumerate(INS))

import sys
import msvcrt

################################################################################

class COD:

    def __init__(self, code):
        for ins in code:
            assert 0 <= ins < len(INS)
        self.cod = code
        self.pos = 0

    def get(self):
        return self.cod[self.pos]

    def inc(self):
        self.pos += 1
        if self.pos == len(self.cod):
            raise SystemExit

    def dec(self):
        self.pos -= 1
        assert self.pos >= 0

################################################################################

class MEM:
    
    def __init__(self):
        self.mem = {}
        self.pos = 0
        
    def get(self):
        if self.pos in self.mem:
            return self.mem[self.pos]
        return 0
    
    def set(self, value):
        if value:
            self.mem[self.pos] = value
        elif self.pos in self.mem:
            del self.mem[self.pos]

    def inc(self):
        self.pos += 1

    def dec (self):
        self.pos -= 1

################################################################################

def parse(string):
    index = 0
    code = []
    ins = string[index:index+3]
    while len(ins) == 3:
        if ins in INS:
            code.append(INS.index(ins))
            index += 3
        else:
            index += 1
        ins = string[index:index+3]
    return tuple(code)

DECODE = ['END', 'P--', 'P++', 'EXE', 'I/O', 'M--',
          'M++', 'LOP', 'M=0', 'REG', 'OUT', 'INP']

def decode(code):
    for ins in code:
        print INS[ins] + '\t' + DECODE[ins]
    print

def engine(code):
    global REG
    REG = None
    mem = MEM()
    cod = COD(code)
    ins = cod.get()
    while True:
        ins = run(mem, cod, ins)

def run(mem, cod, ins):
    global REG
    # INS - 0 - moo
    if ins == 0:
        cod.dec()
        cod.dec()
        # INIT
        level = 1
        temp = cod.get()
        if temp == HLP['moo']:
            level += 1
        elif temp == HLP['MOO']:
            level -= 1
        while level:
            # LOOP
            cod.dec()
            temp = cod.get()
            if temp == HLP['moo']:
                level += 1
            elif temp == HLP['MOO']:
                level -= 1
        return HLP['MOO']
    # INS - 1 - mOo
    elif ins == 1:
        mem.dec()
        cod.inc()
        return cod.get()
    # INS - 2 - moO
    elif ins == 2:
        mem.inc()
        cod.inc()
        return cod.get()
    # INS - 3 - mOO
    elif ins == 3:
        temp = mem.get()
        assert temp != 3
        if 0 <= temp < len(INS):
            return run(mem, cod, temp)
        else:
            raise SystemExit
    # INS - 4 - Moo
    elif ins == 4:
        temp = mem.get()
        if temp:
            sys.stdout.write(chr(temp & 0x7F))
        else:
            char = get_char()
            mem.set(ord(char) & 0x7F)
        cod.inc()
        return cod.get()
    # INS - 5 - MOo
    elif ins == 5:
        mem.set(mem.get() - 1)
        cod.inc()
        return cod.get()
    # INS - 6 - MoO
    elif ins == 6:
        mem.set(mem.get() + 1)
        cod.inc()
        return cod.get()
    # INS - 7 - MOO
    elif ins == 7:
        temp = mem.get()
        if temp:
            cod.inc()
            return cod.get()
        else:
            cod.inc()
            cod.inc()
            # INIT
            level = 1
            temp = cod.get()
            if temp == HLP['moo']:
                level -= 1
            elif temp == HLP['MOO']:
                level += 1
            while level:
                # LOOP
                cod.inc()
                temp = cod.get()
                if temp == HLP['moo']:
                    level -= 1
                elif temp == HLP['MOO']:
                    level += 1
            cod.inc()
            return cod.get()
    # INS - 8 - OOO
    elif ins == 8:
        mem.set(0)
        cod.inc()
        return cod.get()
    # INS - 9 - MMM
    elif ins == 9:
        if REG is None:
            REG = mem.get()
        else:
            mem.set(REG)
            REG = None
        cod.inc()
        return cod.get()
    # INS - 10 - OOM
    elif ins == 10:
        sys.stdout.write(str(mem.get()) + '\n')
        cod.inc()
        return cod.get()
    # INS - 11 - oom
    elif ins == 11:
        mem.set(get_int())
        cod.inc()
        return cod.get()
    # ERROR
    else:
        raise Exception

def get_char():
    while msvcrt.kbhit():
        msvcrt.getch()
    func = False
    char = msvcrt.getch()
    if char in ('\x00', '\xE0'):
        func = True
    while func:
        msvcrt.getch()
        func = False
        char = msvcrt.getch()
        if char in ('\x00', '\xE0'):
            func = True
    return char.replace('\r', '\n')

def get_int():
    while msvcrt.kbhit():
        msvcrt.getch()
    buff = ''
    char = msvcrt.getch()
    while char != '\r' or not buff:
        if '0' <= char <= '9':
            sys.stdout.write(char)
            buff += char
        char = msvcrt.getch()
    sys.stdout.write('\n')
    return int(buff)

################################################################################

def main():
    path = raw_input('Run File: ') + '.cow'
    code = parse(file(path).read())
    decode(code)
    engine(code)
        
################################################################################

if __name__ == '__main__':
    try:
        main()
    except SystemExit:
        raw_input()
    except:
        import traceback
        raw_input(traceback.format_exc())

Several demonstration COW programs can be found below.

BOB

moOMoOMoOMoOMoOmoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMMMmoOMMMMoOMoOMoOMoOMoOMoO
MoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMMMmoOMMMommMoOMoOMoOMoOMoO
MoOMoOMoOMoOMoOMoOMoOMMMmoOMMMMoOMoOMMMmoOMMMMoOMoOMoOMoOMoOMoOMoOMoOMoOMoO
MoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoO
MoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMoOMMMmoOMMMMoOMMMmOomOomOomOo
mOomOoMMMMoOmoOmoOmoOmoOmoOmoOMMMmoOMMMMoOMoOMMMmoOMMMMoOMMMmoOMMMMoOMMMmoO
MMMMoOMoOMMMmoOMMMMoOMMMmoOMMMMoOMoOMMMmoOMMMMoOMMMmoOMMMMoOMoOMMMmoOMMMMoO
MMMmoOMMMMoOMMMmoOMMMMoOMoOMMMmoOMMMMoOMMMmoOMMMMoOMMMmoOMMMMoOMMMmoOMMMMoO
MoOmOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOoMOOOOMmoO
moOmoOmoOmoOmoOMoomoOmoOmoOmoOmoOmoOmoOmoOmoOMoomoOmoOmoOmoOMooMoomOomOomOo
mOomOomOoMoomOomOomOomOomOoMoomOomOomOomOomOomOomOomOoMMMMOoMOOmoOmoOmoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOo
mOomOomOomOomOomOomOomOoOOOmooMMMmoOmoOmoOmoOmoOmoOmoOmoOmOomOomOomOomOomOo
MoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOoMoomOomOomOo
mOomOomOomOoMoomoOmoOmoOmoOMoomoOmoOMooMoomoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOo
mOomOomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoO
moOmoOmoOMoomOoMoomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOoMoomOomOoMoo
mOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoO
moOMoomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoO
moOmoOMooMoomOomOomOomOomOomOomOomOomOomOoMoomOomOoMoomOoOOMmoOmoOmoOmoOmoO
moOMoomoOmoOmoOmoOmoOmoOmoOmoOmoOMoomoOmoOmoOmoOMooMoomOomOomOomOomOomOoMoo
mOomOomOomOomOoMoomOomOomOomOomOomOomOomOoMMMMOoMOOmoOmoOmoOmoOmoOmoOmoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOomOomOomOo
mOomOomOomOoOOOmooMMMmoOmoOmoOmoOmoOmoOmoOmoOmOomOomOomOomOomOoMoomoOmoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOoMoomOomOomOomOomOomOomOo
MoomoOmoOmoOmoOMoomoOmoOMooMoomoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOo
mOomOomOomOomOomOomOomOomOoMoomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoO
moOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoO
moOmoOmoOmoOMoomOomOomOomOoMoomOomOomOomOomOomOoMoomOomOoMMMmOoOOOMoOmoOMOo
MOOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOoMoomOomOomOomOomOomOo
MoomOomOomOomOomOomOomOomOomOoOOOmoOOOOmooMMMmOoMOOmoOmoOmoOmoOmoOmoOmoOmoO
moOmoOmoOmoOMoomoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOo
mOomOomOomOomOomOomOomOomOoOOOmoomoOmoOmoOMoomoOmoOmoOmoOmoOMoomoOmoOmoOmoO
moOmoOmoOmoOMoomoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOoMoomOomOomOomOomOo
mOomOomOomOomOomOoMoomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOo
mOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoo
MoomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoO
moOmoOMoomoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOomOomOo
mOomOomOomOoMoomoOmoOmoOMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOoMoo
moOmoOmoOmoOmoOMoomOomOomOomOomOomOoMoomOomOomOomOomOomOomOoMoomOomOomOomOo
MoomOomOoMoomOoMOoOOMmoOmoOmoOmoOmoOmoOMoomoOmoOmoOmoOmoOmoOmoOmoOmoOMoomoO
moOmoOmoOMooMoomOomOomOomOomOomOoMoomOomOomOomOomOoMoomOomOomOomOomOomOomOo
mOoMMMMOoMOOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOo
mOomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOoOOOmooMMMmoOmoOmoOmoOmoOmoO
moOmoOmOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOo
mOomOomOomOoMoomOomOomOomOomOomOomOoMoomoOmoOmoOmoOMoomoOmoOMooMoomoOmoOmoO
moOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOoMoomoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOoMoomOomOomOomOomOomOomOomOomOomOomOo
mOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOo
mOomOomOomOoMoomOomOoMoomOomOomOomOomOomOoMoomoOmoOmoOmoOmoOmoOmoOmoOmoOmoO
moOmoOmoOmoOmoOmoOmoOmoOmoOMoomOomOomOomOomOomOomOomOomOomOomOomOomOomOomOo
mOoMoomoOmoOmoOmoOmoOmoOmoOmoOMooMoomOomOomOomOomOomOomOomOomOoMoomOomOomOo
MooMoomOomoo

Echo

MoO
MOO
moO
Moo
Moo
OOO
mOo
moo

Fibonacci Generator

MoO     M++     a = 1 #
moO     P++           #
MoO     M++     b = 1 # a = b = 1
mOo     P--
MOO     LOP     while a: # while True:
OOM     OUT          print a  # print a
MMM     REG          temp = a #
moO     P++                   #
moO     P++                   #
MMM     REG          c = temp # c = a #
mOo     P--                   #       #
MMM     REG          temp = b #       #
mOo     P--                   #       #
MMM     REG          a = temp # a = b # c, a = a, b
moO     P++
moO     P++
MOO     LOP          while c:    #
MOo     M--               c -= 1 #
mOo     P--                      #
MoO     M++               b += 1 # b += c
moO     P++
moo     END
mOo     P--
mOo     P--
moo     END