basic.py

##################
# Constants
##################

DIGITS = '0123456789'

##################
# Errors
##################
class Error:
    def __init__(self, error_name, pos_start, pos_end,  details):
        self.pos_start = pos_start
        self.pos_end = pos_end
        self.error_name = error_name
        self.details = details
    
    def as_string(self):
        result = f'{self.error_name}:{self.details}\n'
        result += f'File {self.pos_start.file_name}, line {self.pos_start.line + 1}'
        return result

class IllegalCharError(Error):
    def __init__(self,pos_start, pos_end, details):
        super().__init__('Illegal Character',pos_start, pos_end, details)

##################
# Position
##################
class Position:
    def __init__(self, index, line, column, file_name, file_text):
        self.index = index
        self.line = line
        self.column = column
        self.file_name = file_name
        self.file_text = file_text
    
    def advance(self, current_char):
        self.index += 1
        self.column += 1

        if current_char == '\n':
            self.line += 1
            self.column = 0

        return self
    
    def copy(self):
        return Position(self.index, self.line, self.column, self.file_name, self.file_text)
    


##################
# Tokens
##################
# TT means Token Type
TT_INT = 'INT'
TT_FLOAT = 'FLOAT'

TT_PLUS = 'PLUS'
TT_MINUS = 'MINUS'
TT_MUL = 'MUL'
TT_DIV = 'DIV'

TT_LPAREN = 'LPAREN'
TT_RPAREN = 'RPAREN'


class Token:
    def __init__(self, type_, value=None):
        self.type = type_
        self.value = value

    def __repr__(self):
        if self.value:
            return f'{self.type}:{self.value}'
        return f'{self.type}'


###########################
# LEXER
###########################

class Lexer:
    def __init__(self, file_name, text):
        """text: the text we will be processing
        pos: keep track of current position
        current_char: keep track of current character"""

        self.file_name = file_name
        self.text = text
        self.pos = Position(-1, 0, -1, file_name, file_text=text)
        self.current_char = None
        self.advance()

    def advance(self):
        self.pos.advance(self.current_char)
        self.current_char = self.text[self.pos.index] if self.pos.index < len(self.text) else None
    
    def make_tokens(self):
        tokens = []

        while self.current_char != None:
            if self.current_char in ' \t':
                self.advance()
            elif self.current_char in DIGITS:
                tokens.append(self.make_number())
            elif self.current_char == '+':
                tokens.append(Token(TT_PLUS))
                self.advance()
            elif self.current_char == '-':
                tokens.append(Token(TT_MINUS))
                self.advance()
            elif self.current_char == '*':
                tokens.append(Token(TT_MUL))
                self.advance()
            elif self.current_char == '/':
                tokens.append(Token(TT_DIV))
                self.advance()
            elif self.current_char == '(':
                tokens.append(Token(TT_LPAREN))
                self.advance()
            elif self.current_char == ')':
                tokens.append(Token(TT_RPAREN))
                self.advance()
            else:
                pos_start = self.pos.copy()
                char = self.current_char
                self.advance()
                return [], IllegalCharError(pos_start, self.pos,  f"'{char}'")

        return tokens, None
    
    def make_number(self):
        '''creats number one digit at a time'''
        '''[dot_count] to detect float or int'''
        num_str = ''
        dot_count = 0

        while self.current_char != None and self.current_char in DIGITS + '.':
            if self.current_char == '.':
                if dot_count == 1 : break
                dot_count += 1
                num_str += '.'
            else:
                num_str += self.current_char
            self.advance()

        if dot_count == 0:
            return Token(TT_INT, int(num_str))
        else:
            return Token(TT_FLOAT, float(num_str))

def run(file_name, text):
    lexer = Lexer(file_name, text)
    tokens, error = lexer.make_tokens()

    return tokens, error