class Parser():
'''Class Parser look at next token'''
A_COMMAND = 0
C_COMMAND = 1
L_COMMAND = 2
def __init__(self, file):
self.lex = Lexicon(file)
self._init_cmd_info()
def _init_cmd_info(self):
self._cmd_type = -1
self._symbol = ''
self._dest = ''
self._comp = ''
self._jmp = ''
def __str__(self):
pass
def has_more_commands(self):
return self.lex.has_more_commands()
# Get the next entire command - each command resides on its own line.
def advance(self):
self._init_cmd_info()
self.lex.next_command()
tok, val = self.lex.cur_token
if tok == self.lex.OP and val == '@':
self._a_command()
elif tok == self.lex.OP and val == '(':
self._l_command()
else:
self._c_command(tok, val)
# The following functions contain the extracted parts of the command.
def command_type(self):
return self._cmd_type
def symbol(self):
return self._symbol
def dest(self):
return self._dest
def comp(self):
return self._comp
def jmp(self):
return self._jmp
# @symbol or @number
def _a_command(self):
self._cmd_type = Parser.A_COMMAND
tok_type, self._symbol = self.lex.next_token()
# (symbol)
def _l_command(self):
self._cmd_type = Parser.L_COMMAND
tok_type, self._symbol = self.lex.next_token()
# dest=comp;jump
# dest=comp omitting jump
# comp;jump omitting dest
# comp omitting dest and jump
def _c_command(self, tok1, val1):
self._cmd_type = Parser.C_COMMAND
comp_tok, comp_val = self._get_dest(tok1, val1)
self._get_comp(comp_tok, comp_val)
self._get_jump()
# Get the 'dest' part if any. Return the first token of the 'comp' part.
def _get_dest(self, tok1, val1):
tok2, val2 = self.lex.peek_token()
if tok2 == self.lex.OP and val2 == '=':
self.lex.next_token()
self._dest = val1
comp_tok, comp_val = self.lex.next_token()
else:
comp_tok, comp_val = tok1, val1
return (comp_tok, comp_val)
# Get the 'comp' part - must be present.
def _get_comp(self, tok, val):
if tok == self.lex.OP and (val == '-' or val == '!'):
tok2, val2 = self.lex.next_token()
self._comp = val + val2
elif tok == self.lex.NUM or tok == self.lex.ID:
self._comp = val
tok2, val2 = self.lex.peek_token()
if tok2 == self.lex.OP and val2 != ';':
self.lex.next_token()
tok3, val3 = self.lex.next_token()
self._comp += val2 + val3
# Get the 'jump' part if any
def _get_jump(self):
tok, val = self.lex.next_token()
if tok == self.lex.OP and val == ';':
jump_tok, jump_val = self.lex.next_token()
self._jmp = jump_val
