pl0_compiler.py

#!/usr/bin/env python
#
# Copyright (c) 2012 Samuel G. D. Williams. <http://www.oriontransfer.co.nz>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#

import os
import sys
import StringIO
import pl0_parser
from pl0_node_visitor import StackingNodeVisitor

class Compiler(StackingNodeVisitor):

    def __init__(self):
        super(Compiler, self).__init__()
        self.label_id = 0

    def intermediate_label(self, hint = ''):
        self.label_id += 1
        return 't_' + hint + '_' + `self.label_id`

    def generate(self, node):
        self.push()
        result = self.visit_node(node)
        return [self.pop(), result]

    def accept_variables(self, *node):
        for var in node[1:]:
            # Generate a unique name for the variable
            variable_name = self.intermediate_label('var_' + var[1])
            
            # Save the unique name for loading this variable in the future.
            self.stack[-1].update(var[1], variable_name)
            
            # Allocate static storage space for the variable
            print variable_name + ":"
            print "    0"
    
    def accept_constants(self, *node):
        for var in node[1:]:
            self.stack[-1].define(var[1], var[2])

    def accept_procedures(self, *node):
        for proc in node[1:]:
            # Generate a unique name for the procedure
            proc_name = self.intermediate_label('proc_' + proc[1])

            # Save the unique procedure name on the lexical stack
            self.stack[-1].declare(proc[1], proc_name)

            # Define a new lexical scope
            self.push()

            # Generate any static storage required by the procedure
            print "# Procedure " + proc[1]
            self.visit_expressions(proc[2][1:3])

            # Generate the code for the procedure
            print proc_name + ":"
            self.visit_node(proc[2][4])
            print "\tRET"

            # Finished with lexical scope
            self.pop()

    def accept_program(self, *node):
        print "JMP main"

        block = node[1]
        self.visit_expressions(block[1:4])

        print "main:"
        self.visit_node(block[4])
        print "\tHALT"

    def accept_while(self, *node):
        top_label = self.intermediate_label("while_start")
        bottom_label = self.intermediate_label("while_end")

        condition = node[1]
        loop = node[2]

        print top_label + ":"
        # Result of condition is on top of stack
        self.visit_node(condition)

        print "\tJE " + bottom_label

        self.visit_node(loop)

        print "\tJMP " + top_label
        print bottom_label + ":"

    def accept_if(self, *node):
        false_label = self.intermediate_label("if_false")

        condition = node[1]
        body = node[2]

        self.visit_node(condition)

        print "\tJE " + false_label

        self.visit_node(body)

        print false_label + ":"

    def accept_condition(self, *node):
        operator = node[2]
        lhs = node[1]
        rhs = node[3]

        self.visit_node(lhs)
        self.visit_node(rhs)

        print "\tCMP" + operator

    def accept_set(self, *node):
        name = node[1][1]

        self.visit_node(node[2])

        assign_to = node[1][1]
        defined, value, level = self.find(assign_to)

        if defined != 'VARIABLE':
            raise NameError("Invalid assignment to non-variable " + assign_to + " of type " + defined)

        print "\tSAVE " + value

    def accept_call(self, *node):
        defined, value, level = self.find(node[1])

        if defined != 'PROCEDURE':
            raise NameError("Expecting procedure but got: " + defined)

        print "\tCALL " + value

    def accept_term(self, *node):
        self.visit_node(node[1])

        for term in node[2:]:
            self.visit_node(term[1])

            if term[0] == 'TIMES':
                print "\tMUL"
            elif term[0] == 'DIVIDES':
                print "\tDIV"

    def accept_expression(self, *node):
        # Result of this expression will be on the top of stack
        self.visit_node(node[2])

        for term in node[3:]:
            self.visit_node(term[1])

            if term[0] == 'PLUS':
                print "\tADD"
            elif term[0] == 'MINUS':
                print "\tSUB"

        if node[1] == 'MINUS':
            print "\tPUSH -1"
            print "\tMUL"

    def accept_print(self, *node):
        self.visit_node(node[1])
        print "\tPRINT"
        print "\tPOP"

    def accept_number(self, *node):
        print "\tPUSH " + `node[1]`

    def accept_name(self, *node):
        defined, value, level = self.find(node[1])

        if defined == 'VARIABLE':
            print "\tLOAD", value
        elif defined == 'CONSTANT':
            print "\tPUSH", value
        else:
            raise NameError("Invalid value name " + node[1] + " of type " + defined)

if __name__ == '__main__':
    code = sys.stdin.read()
    parser = pl0_parser.Parser()
    parser.input(code)
    program = parser.p_program()

    compiler = Compiler()
    compiler.generate(program)