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lexer.py
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lexer.py
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from typing import TextIO
from enum import Enum, auto
import re
class TokenType(Enum):
EOF = auto()
ERR = auto()
DIRECTIVE = auto()
# label represents opcode, label name or type. Which of these it is is
# determined by parser based on context.
LABEL = auto()
IDENT = auto()
NIL = auto()
BOOL = auto()
INT = auto()
STRING = auto()
TYPE = auto()
class Token:
"""Contains the token type and string value of the token."""
def __init__(self, typ: TokenType, value: str = ""):
self.type = typ
self.value = value
# regexes for checking validity of some tokens
# Checks for valid identifiers, labels or instructions
_IDENT_RE = re.compile(r"[A-Za-z_\-$&%*!?][0-9A-Za-z_\-$&%*!?]*")
# Checks for valid integer literals
_INT_RE = re.compile(r"[+\-]?([0-9][0-9_]*|0x[0-9A-Fa-f_]*|0o[0-7_]*)")
# checks for valid string literals
_STRING_RE = re.compile(r"([^\\]|\\[0-9][0-9][0-9])*")
class Lexer:
def __init__(self, input: TextIO) -> None:
# The input stream
self.input = input
# comments will be ignored with tokenization, the stats about them must
# be collected here
self.comment_count = 0
def next(self) -> list[Token]:
"""Gets the next token"""
n = self._read_next();
while not n:
n = self._read_next();
return n
def _read_next(self) -> list[Token]:
"""Reads next line of input and creates it into tokens"""
# read next line and check for eof
line = self.input.readline()
if not line:
return [Token(TokenType.EOF)]
queue: list[Token] = []
for s in line.split():
# check for comments
spl = s.split('#', maxsplit=1)
if spl[0]:
t = Lexer._parse_token(spl[0]);
if t.type == TokenType.ERR:
return [t]
queue.append(t)
if len(spl) > 1:
self.comment_count += 1;
return queue
return queue
@staticmethod
def _parse_token(s: str) -> Token:
# check for special directives (e.g. '.IPPcode24')
if s[0] == ".":
return Token(TokenType.DIRECTIVE, s)
# empty string literals are special case where there is nothing after
# the `@` symbol
if s == "string@":
return Token(TokenType.STRING)
# split by `@`, if there is no `@` it is label, otherwise the first
# of the splitted array will determine the token type
spl = s.split("@")
if len(spl) == 1:
return Lexer._parse_label(s)
# string literals can contain `@`
if len(spl) > 2:
if spl[0] == "string":
return Lexer._parse_string("@".join(spl[1:]))
return Token(
TokenType.ERR,
f"unexpected character '@' in '{s}'"
)
type = spl[0]
value = spl[1]
# check for the type of the token
match type:
case "TF" | "LF" | "GF":
return Lexer._parse_ident(s)
case "nil":
return Lexer._parse_nil(value)
case "bool":
return Lexer._parse_bool(value)
case "int":
return Lexer._parse_int(value)
case "string":
return Lexer._parse_string(value)
case _:
return Token(
TokenType.ERR,
f"Unknown data type '{type}'"
)
@staticmethod
def _parse_label(s: str) -> Token:
if _IDENT_RE.fullmatch(s):
return Token(TokenType.LABEL, s.replace("&", "&"))
return Token(TokenType.ERR, f"Invalid label name '{s}'")
@staticmethod
def _parse_ident(s: str) -> Token:
# `s` also contains the frame, run the checks only on the name
id = s[3:]
if _IDENT_RE.fullmatch(id):
return Token(TokenType.IDENT, s.replace("&", "&"))
return Token(TokenType.ERR, f"Invalid variable name '{s}'")
@staticmethod
def _parse_nil(s: str) -> Token:
if s == "nil":
return Token(TokenType.NIL, "nil")
return Token(TokenType.ERR, "type 'nil' can only have value 'nil'")
@staticmethod
def _parse_bool(s: str) -> Token:
match s:
case "true":
return Token(TokenType.BOOL, "true")
case "false":
return Token(TokenType.BOOL, "false")
case _:
return Token(TokenType.ERR, f"Invalid bool value '{s}'")
@staticmethod
def _parse_int(s: str) -> Token:
if _INT_RE.fullmatch(s):
return Token(TokenType.INT, s)
return Token(TokenType.ERR, f"Invalid int value '{s}'")
@staticmethod
def _parse_string(s: str) -> Token:
if _STRING_RE.fullmatch(s):
return Token(
TokenType.STRING,
s.replace("&", "&")
.replace("<", "<")
.replace(">", ">")
)
return Token(TokenType.ERR, f"Invalid string value '{s}'")