vm.py

def pairs(l):
    return zip(l[::2], l[1::2])

def vm(ops, env={}):
    class closure:
        def __init__(self, pc, env): self.pc, self.env = pc, env
    def popn(n):
        if len(stack) < n: print 'not enough elements for pop: %d needed, %d left' % (n, len(stack))
        top = stack[-n:]
        stack[-n:] = []
        return top
    pc, stack, fstack = 0, [], []
    labels = {op[1]: index for index, op in enumerate(ops) if op[0] == 'label'}
    while pc < len(ops):
        op, args, pc = ops[pc][0], ops[pc][1:], pc + 1
        arg = args[0] if args else None
        if op == 'label':
            pass
        elif op == 'val':
            stack.append(arg)
        elif op == 'fn':
            stack.append(closure(labels[arg], env))
        elif op == 'set' or op == 'get':
            e = env
            while e is not None and arg not in e:
                e = e[''] if '' in e else None
            if op == 'set': (env if e is None else e)[arg] = stack.pop()
            elif op == 'get':
                if e: stack.append(e[arg])
                else: print('undefined variable %s' % arg)
        elif op == 'arr':
            stack.append(popn(arg))
        elif op == 'map':
            stack.append(dict(pairs(popn(arg * 2))))
        elif op == 'call' or op == 'tcall':
            fn = stack.pop()
            if args and arg:
                stack.append(popn(arg))
            if isinstance(fn, closure):
                if op == 'call':
                    fstack.append((pc, env))
                pc, env = fn.pc, {'': fn.env}
            elif hasattr(fn, '__call__'):
                stack.append(fn(stack.pop()))
        elif op == 'args':
            vals = stack.pop()
            if len(args) != len(vals): print 'warning: wrong arguments count: %d expected, %d given' % (len(args), len(vals))
            env.update(dict(zip(args, vals)))
        elif op == 'ret':
            if not fstack: break
            pc, env = fstack.pop()
        elif op == 'jmp':
            pc = labels[arg]
        elif op == 'jmpf':
            if not stack.pop(): pc = labels[arg]