parser.py

#!/usr/bin/python
# author: imlach
# file: parser.py
import drawFunctions, sys
from string import *


fns = drawFunctions.draw()

##
# Prompt the user for a filename, if not supplied as the first
# command line arg.
def filePrompt(args=[]):
    if len(args) > 1:
        fName = args[1]
    else:
        fName = raw_input("Please enter your filename: ")


    try:
        lstFile = open(fName,"r")
        return lstFile,fName
    except IOError:
        print "Error opening file "+fName+"..."
        return filePrompt(),fName


##
# Defines what commands are recognised, and how to handle them.
# returns a pair of vals, used for different things
def execFn(fnStr, args, defs):

    ## Little 'hack' to check if parameters are numerical.
    for arg in args[1:]:
        try:
            float(arg)
        except ValueError:
            return "valErr",arg

    ## Begin working things out
    if fnStr == "position":
        fns.pos(args[1],args[2])
        return fnStr,True
    elif fnStr == "move":
        fns.mov(args[1],args[2])
        return fnStr,True
    elif fnStr == "line":
        fns.line(args[1],args[2])
        return fnStr,True
    elif fnStr == "circle":
        fns.circ(args[1])
        return fnStr,True
    elif fnStr == "define":
        defs[args[1]] = []
        curDef = args[1]
        return fnStr,args[1]
    elif fnStr == "end":
        return fnStr,""
    elif fnStr in defs.keys():
        ## Execute function call
        for line in defs[fnStr]:
            execFn(line[0],line,defs)
        return fnStr,True
    elif fnStr == "" or fnStr[0] == "#":
        #Ignore comments or blank lines
        pass
        return "",""
    else:
        return "error",False


##
# Runs through the file returned by filePrompt, and goes through
# each line.
def parse(listing,fName):

    ## Set up vars and objects.

    defs = {}
    lines = []
    curDef = ""
    i = 0
    loops = 0
    backTo = 0

    for line in listing:
        line = split(line[:-1]," ")
        lines += [line]

    while i < len(lines):
        line = lines[i]


        if line[0] == "loop":
            ## If in loop mode, store the number of loops and which line
            #  to return to.
            loops = int(line[1])-1
            backTo = i
        elif curDef != "" and line[0] != "end":
            ## Add line to def if in define mode
            defs[curDef] += [line]
        else:
            ## Execute current line
            rtVal = execFn(line[0],line,defs)
            if rtVal[0] == "define":
                # Enter define mode
                curDef = rtVal[1]
            elif rtVal[0] == "end":
                if loops == 0:
                    # If not in loop mode, exit define mode
                    curDef = rtVal[1]
                else:
                    # Decrement loop counter, and return to the line i,
                    # so it gets incremented so to be on the correct
                    # line in the next loop.
                    loops -= 1
                    i = backTo

            ## Handle errors nicely
            elif rtVal[0] == "error":
                print "Syntax error on line "+str(i+1)+" of "+fName+": '"+line[0]+"'"
                return False
            elif rtVal[0] == "valErr":
                print "Value error on line "+str(i+1)+" of "+fName+": '"+rtVal[1]+"'"
                return False


        i += 1

    fns.complete()
    return True


lst = filePrompt(sys.argv)
parse(lst[0],lst[1])