ite.py

#!/usr/bin/env python

def ite_interpretter(prog,inp):
    state = {'0':0, '1':1}
    for i,char in enumerate(inp):
        if char!='0' and char!='1':
            raise Exception("Invalid input character '%s'"%char)
        state['I%d'%i] = int(char)
    output = 0 # default value for empty programs
    output_num = 0
    line_num = 0
    for line in prog.splitlines():
        line_num += 1
        # allow comments and blank lines
        if line=="" or line[0]=="#":
            continue
        terms = line.rstrip().split(' ')
        try:
            # optionally allow custom names
            if len(terms) == 3:
                name=None
            elif len(terms) == 4:
                name=terms[0]
                del terms[0]
                if len(name)<2 or name[-1]!=":" or (name[0] in ['Q','I']):
                    raise Exception("invalid custom name specifier")
                name=name[:-1]
            else:
                raise Exception("invalid number of terms")
            terms = [state[x] for x in terms]
        except Exception as e:
            raise Exception("Error parsing line %d: %r, %s"%(line_num,line,e))
        output = terms[1] if terms[0] else terms[2]
        if name:
            state[name] = output
        state['Q%d'%output_num] = output
        output_num += 1
    return output

if __name__ == "__main__":
    import sys
    if len(sys.argv)<3:
        print "Usage: python ite.py <prog> <input>"
        sys.exit(1)

    prog=open(sys.argv[1]).read()
    inp=sys.argv[2]

    print ite_interpretter(prog,inp)