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lexer.py
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lexer.py
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from threading import Thread
from string import ascii_letters, digits
from queue import Queue
# Lexer
class Lexer(Thread):
"""
Handles all lexing.
Threaded because parsing can start before lexing finishes
every token consumed by _lex_{token_name} function
"""
def __init__(self, source, que, name="No Name"):
super().__init__()
self._source = source # source code here
self._que = que
self._start = 0 # holds the begining of next token
self._pos = 0 # current cursor position
self.name = name
self._line = 1
self.keywords = ("if", "else", "while", "for", "fn", "print", "let")
self._opertors = [
"+",
"-",
"*",
"/",
"=",
":",
"==",
"<",
">",
"|",
"&",
",",
"::",
]
self.operators = self._opertors
self.indentlevels = [0]
def run(self):
"""
heart of the lexer
works as a state machine
"""
state = self._lex_initial
while True:
try:
state = state() # Function changes itself to handle next state starting from _lex_initial
except Consumed:
self._cleanup()
break
except LexException as e:
print(e)
self._add("END") # EOF
break
def _add(self, token_type, value=None):
""" After _lex functions determine what is a token, they call this to consume """
self._que.put((token_type, self._line, self._source[self._start : self._pos]))
self._start = self._pos
def _lex_initial(self):
"""
This function reads char by char to determine which function can
correctly identify next token.
Returns the function that can handle it.
(except simple operators. they can be consumed directly)
"""
while True:
current = self._current_char()
if current in ascii_letters:
return self._lex_name
elif current in digits:
return self._lex_number
elif current == '"':
self._pos += 1
return self._lex_string
elif current in self._opertors:
self._pos += 1
if self._current_char() == "*" and current == "*":
self._pos += 1
self._add("**")
elif self._current_char() == "/" and current == "/":
self._pos += 1
self._add("//")
elif self._current_char() == "=" and current == "=":
self._pos += 1
self._add("==")
elif self._current_char() == ":" and current == ":":
self._pos += 1
self._add("::")
else:
self._add(current)
elif current in " \t":
self._pos += 1
self._start = self._pos
elif current == "\n":
self._line += 1
self._pos += 1
self._start = self._pos
self._add("NEWLINE")
return self._lex_indent
elif current == "(":
self._pos += 1
self._add("LEFT_PAREN")
self._start = self._pos
elif current == ")":
self._pos += 1
self._add("RIGHT_PAREN")
self._start = self._pos
elif current == "#":
self._pos += 1
while True:
current = self._current_char()
self._pos += 1
if current == "\n":
self._start = self._pos
return self._lex_initial
else:
raise LexException("Unknown character at line " + str(self._line))
def _current_char(self):
try:
return self._source[self._pos]
except IndexError:
raise Consumed("Input END")
def _lex_string(self):
escape = False
while True:
try:
current = self._current_char()
except Consumed:
raise LexException("Unclosed string????")
self._pos += 1
if escape:
escape = False
continue
if current == "\\":
escape = True
elif current == '"':
self._add("STRING")
return self._lex_initial()
elif current == "\n":
self._line += 1
self._pos += 1
self._start = self._pos
def _lex_number(self):
while True:
try:
current = self._current_char()
except Consumed:
self._add("NUMBER")
raise
if current in digits:
self._pos += 1
elif current == ".":
self._pos += 1
return self._lex_float()
else:
if (
current != " "
and current not in self._opertors
and current != "("
and current != ")"
and current != "\n"
):
raise LexException(
f"Integer error at line {self._line } (( {current} ))"
)
else:
self._add("NUMBER")
# self._pos += 1
return self._lex_initial
def _lex_float(self):
while True:
try:
current = self._current_char()
except Consumed:
self._add("FLOAT")
raise
if current in digits:
self._pos += 1
else:
if (
current != " "
and current not in self._opertors
and current != "("
and current != ")"
and current != "\n"
):
raise LexException(f"Float error at line {self._line }")
else:
self._add("FLOAT")
self._pos += 1
return self._lex_initial
def _lex_name(self):
def add_keyword_or_name():
token = self._source[self._start : self._pos]
if token in self.keywords:
return self._add("KEYWORD")
elif token in ["True", "False"]:
return self._add("BOOL")
else:
return self._add("NAME")
while True:
try:
current = self._current_char()
except Consumed:
add_keyword_or_name()
raise
if current in ascii_letters:
self._pos += 1
else:
add_keyword_or_name()
return self._lex_initial
def _lex_indent(self):
current_indent = 0
while True:
current = self._current_char()
if current == " ":
self._pos += 1
current_indent += 1
elif current == "\t":
self._pos += 1
current_indent += 4
elif current == "\n":
self._pos += 1
current_indent = 0
else:
if current_indent < self.indentlevels[-1]:
if current_indent in self.indentlevels:
while True:
if current_indent < self.indentlevels[-1]:
self._add("DEDENT")
self.indentlevels.pop()
else:
return self._lex_initial
else:
raise LexException(
"Congratz! Your indentation is all messed up!"
)
elif current_indent > self.indentlevels[-1]:
self._add("INDENT")
self.indentlevels.append(current_indent)
return self._lex_initial
else:
# yeni tokeni indentten sonra başlat
self._start = self._pos
return self._lex_initial
def _cleanup(self):
current_indentation = self.indentlevels.pop()
while current_indentation != 0:
self._add("DEDENT")
current_indentation = self.indentlevels.pop()
self._add("END")
class Consumed(Exception):
pass
class LexException(Exception):
pass
### FOR TESTING PURPOSES. PRINTS TO TOKENS TO SEE
if __name__ == "__main__":
import sys
def source_read():
if len(sys.argv) > 1:
with open(sys.argv[1]) as ff:
data = ff.read()
return data
else:
sys.exit()
q = Queue()
ll = Lexer(source_read(), q)
ll.start()
while True:
ttype, line, tvalue = q.get()
print(ttype, line, tvalue)
if ttype == "END":
break