basic.py

#######################################
# IMPORTS
#######################################

from strings_with_arrows import *

import string

#######################################
# CONSTANTS
#######################################

DIGITS = "0123456789"
LETTERS = string.ascii_letters
LETTERS_DIGITS = LETTERS + DIGITS

#######################################
# ERRORS
#######################################


class Error:
    def __init__(self, pos_start, pos_end, error_name, 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.fn}, line {self.pos_start.ln + 1}"
        result += "\n\n" + string_with_arrows(
            self.pos_start.ftxt, self.pos_start, self.pos_end
        )
        return result


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


class ExpectedCharError(Error):
    def __init__(self, pos_start, pos_end, details):
        super().__init__(pos_start, pos_end, "Expected Character", details)


class InvalidSyntaxError(Error):
    def __init__(self, pos_start, pos_end, details=""):
        super().__init__(pos_start, pos_end, "Invalid Syntax", details)


class RTError(Error):
    def __init__(self, pos_start, pos_end, details, context):
        super().__init__(pos_start, pos_end, "Runtime Error", details)
        self.context = context

    def as_string(self):
        result = self.generate_traceback()
        result += f"{self.error_name}: {self.details}"
        result += "\n\n" + string_with_arrows(
            self.pos_start.ftxt, self.pos_start, self.pos_end
        )
        return result

    def generate_traceback(self):
        result = ""
        pos = self.pos_start
        ctx = self.context

        while ctx:
            result = (
                f"  File {pos.fn}, line {str(pos.ln + 1)}, in {ctx.display_name}\n"
                + result
            )
            pos = ctx.parent_entry_pos
            ctx = ctx.parent

        return "Traceback (most recent call last):\n" + result


#######################################
# POSITION
#######################################


class Position:
    def __init__(self, idx, ln, col, fn, ftxt):
        self.idx = idx
        self.ln = ln
        self.col = col
        self.fn = fn
        self.ftxt = ftxt

    def advance(self, current_char=None):
        self.idx += 1
        self.col += 1

        if current_char == "\n":
            self.ln += 1
            self.col = 0

        return self

    def copy(self):
        return Position(self.idx, self.ln, self.col, self.fn, self.ftxt)


#######################################
# TOKENS
#######################################

TT_INT = "INT"
TT_FLOAT = "FLOAT"
TT_STRING = "STRING"
TT_IDENTIFIER = "IDENTIFIER"
TT_KEYWORD = "KEYWORD"
TT_PLUS = "PLUS"
TT_MINUS = "MINUS"
TT_MUL = "MUL"
TT_DIV = "DIV"
TT_POW = "POW"
TT_EQ = "EQ"
TT_LPAREN = "LPAREN"
TT_RPAREN = "RPAREN"
TT_EE = "EE"
TT_NE = "NE"
TT_LT = "LT"
TT_GT = "GT"
TT_LTE = "LTE"
TT_GTE = "GTE"
TT_COMMA = "COMMA"
TT_ARROW = "ARROW"
TT_EOF = "EOF"

KEYWORDS = [
    "VAR",
    "AND",
    "OR",
    "NOT",
    "IF",
    "ELIF",
    "ELSE",
    "FOR",
    "TO",
    "STEP",
    "WHILE",
    "FUN",
    "THEN",
]


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

        if pos_start:
            self.pos_start = pos_start.copy()
            self.pos_end = pos_start.copy()
            self.pos_end.advance()

        if pos_end:
            self.pos_end = pos_end.copy()

    def matches(self, type_, value):
        return self.type == type_ and 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, fn, text):
        self.fn = fn
        self.text = text
        self.pos = Position(-1, 0, -1, fn, text)
        self.current_char = None
        self.advance()

    def advance(self):
        self.pos.advance(self.current_char)
        self.current_char = (
            self.text[self.pos.idx] if self.pos.idx < 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 in LETTERS:
                tokens.append(self.make_identifier())
            elif self.current_char == '"':
                tokens.append(self.make_string())
            elif self.current_char == "+":
                tokens.append(Token(TT_PLUS, pos_start=self.pos))
                self.advance()
            elif self.current_char == "-":
                tokens.append(self.make_minus_or_arrow())
            elif self.current_char == "*":
                tokens.append(Token(TT_MUL, pos_start=self.pos))
                self.advance()
            elif self.current_char == "/":
                tokens.append(Token(TT_DIV, pos_start=self.pos))
                self.advance()
            elif self.current_char == "^":
                tokens.append(Token(TT_POW, pos_start=self.pos))
                self.advance()
            elif self.current_char == "(":
                tokens.append(Token(TT_LPAREN, pos_start=self.pos))
                self.advance()
            elif self.current_char == ")":
                tokens.append(Token(TT_RPAREN, pos_start=self.pos))
                self.advance()
            elif self.current_char == "!":
                token, error = self.make_not_equals()
                if error:
                    return [], error
                tokens.append(token)
            elif self.current_char == "=":
                tokens.append(self.make_equals())
            elif self.current_char == "<":
                tokens.append(self.make_less_than())
            elif self.current_char == ">":
                tokens.append(self.make_greater_than())
            elif self.current_char == ",":
                tokens.append(Token(TT_COMMA, pos_start=self.pos))
                self.advance()
            else:
                pos_start = self.pos.copy()
                char = self.current_char
                self.advance()
                return [], IllegalCharError(pos_start, self.pos, "'" + char + "'")

        tokens.append(Token(TT_EOF, pos_start=self.pos))
        return tokens, None

    def make_number(self):
        num_str = ""
        dot_count = 0
        pos_start = self.pos.copy()

        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 += self.current_char
            self.advance()

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

    def make_string(self):
        string = ''
        pos_start = self.pos.copy()
        escape_character = {
            'n': '\n',
            't': '\t'
        }
        self.advance()

        while self.current_char != None and (self.current_char != '"' or escape_character):
            if escape_character:
                string += escape_character.get(self.current_char, self.current_char)
            else:
                if self.current_char == '\\':
                    escape_character = True
                else:
                    string += self.current_char
            self.advance()
            escape_character = False
        
        self.advance()
        return Token(TT_STRING, string, pos_start, self.pos)

    def make_identifier(self):
        id_str = ""
        pos_start = self.pos.copy()

        while self.current_char != None and self.current_char in LETTERS_DIGITS + "_":
            id_str += self.current_char
            self.advance()

        tok_type = TT_KEYWORD if id_str in KEYWORDS else TT_IDENTIFIER
        return Token(tok_type, id_str, pos_start, self.pos)

    def make_minus_or_arrow(self):
        tok_type = TT_MINUS
        pos_start = self.pos.copy()
        self.advance()

        if self.current_char == ">":
            self.advance()
            tok_type = TT_ARROW

        return Token(tok_type, pos_start=pos_start, pos_end=self.pos)

    def make_not_equals(self):
        pos_start = self.pos.copy()
        self.advance()

        if self.current_char == "=":
            self.advance()
            return Token(TT_NE, pos_start=pos_start, pos_end=self.pos), None

        self.advance()
        return None, ExpectedCharError(pos_start, self.pos, "'=' (after '!')")

    def make_equals(self):
        tok_type = TT_EQ
        pos_start = self.pos.copy()
        self.advance()

        if self.current_char == "=":
            self.advance()
            tok_type = TT_EE

        return Token(tok_type, pos_start=pos_start, pos_end=self.pos)

    def make_less_than(self):
        tok_type = TT_LT
        pos_start = self.pos.copy()
        self.advance()

        if self.current_char == "=":
            self.advance()
            tok_type = TT_LTE

        return Token(tok_type, pos_start=pos_start, pos_end=self.pos)

    def make_greater_than(self):
        tok_type = TT_GT
        pos_start = self.pos.copy()
        self.advance()

        if self.current_char == "=":
            self.advance()
            tok_type = TT_GTE

        return Token(tok_type, pos_start=pos_start, pos_end=self.pos)


#######################################
# NODES
#######################################


class NumberNode:
    def __init__(self, tok):
        self.tok = tok

        self.pos_start = self.tok.pos_start
        self.pos_end = self.tok.pos_end

    def __repr__(self):
        return f"{self.tok}"

class StringNode:
    def __init__(self, tok):
        self.tok = tok

        self.pos_start = self.tok.pos_start
        self.pos_end = self.tok.pos_end

    def __repr__(self):
        return f"{self.tok}"


class VarAccessNode:
    def __init__(self, var_name_tok):
        self.var_name_tok = var_name_tok

        self.pos_start = self.var_name_tok.pos_start
        self.pos_end = self.var_name_tok.pos_end


class VarAssignNode:
    def __init__(self, var_name_tok, value_node):
        self.var_name_tok = var_name_tok
        self.value_node = value_node

        self.pos_start = self.var_name_tok.pos_start
        self.pos_end = self.value_node.pos_end


class BinOpNode:
    def __init__(self, left_node, op_tok, right_node):
        self.left_node = left_node
        self.op_tok = op_tok
        self.right_node = right_node

        self.pos_start = self.left_node.pos_start
        self.pos_end = self.right_node.pos_end

    def __repr__(self):
        return f"({self.left_node}, {self.op_tok}, {self.right_node})"


class UnaryOpNode:
    def __init__(self, op_tok, node):
        self.op_tok = op_tok
        self.node = node

        self.pos_start = self.op_tok.pos_start
        self.pos_end = node.pos_end

    def __repr__(self):
        return f"({self.op_tok}, {self.node})"


class IfNode:
    def __init__(self, cases, else_case):
        self.cases = cases
        self.else_case = else_case

        self.pos_start = self.cases[0][0].pos_start
        self.pos_end = (self.else_case or self.cases[len(self.cases) - 1][0]).pos_end


class ForNode:
    def __init__(
        self, var_name_tok, start_value_node, end_value_node, step_value_node, body_node
    ):
        self.var_name_tok = var_name_tok
        self.start_value_node = start_value_node
        self.end_value_node = end_value_node
        self.step_value_node = step_value_node
        self.body_node = body_node

        self.pos_start = self.var_name_tok.pos_start
        self.pos_end = self.body_node.pos_end


class WhileNode:
    def __init__(self, condition_node, body_node):
        self.condition_node = condition_node
        self.body_node = body_node

        self.pos_start = self.condition_node.pos_start
        self.pos_end = self.body_node.pos_end


class FuncDefNode:
    def __init__(self, var_name_tok, arg_name_toks, body_node):
        self.var_name_tok = var_name_tok
        self.arg_name_toks = arg_name_toks
        self.body_node = body_node

        if self.var_name_tok:
            self.pos_start = self.var_name_tok.pos_start
        elif len(self.arg_name_toks) > 0:
            self.pos_start = self.arg_name_toks[0].pos_start
        else:
            self.pos_start = self.body_node.pos_start

        self.pos_end = self.body_node.pos_end


class CallNode:
    def __init__(self, node_to_call, arg_nodes):
        self.node_to_call = node_to_call
        self.arg_nodes = arg_nodes

        self.pos_start = self.node_to_call.pos_start

        if len(self.arg_nodes) > 0:
            self.pos_end = self.arg_nodes[len(self.arg_nodes) - 1].pos_end
        else:
            self.pos_end = self.node_to_call.pos_end


#######################################
# PARSE RESULT
#######################################


class ParseResult:
    def __init__(self):
        self.error = None
        self.node = None
        self.last_registered_advance_count = 0
        self.advance_count = 0

    def register_advancement(self):
        self.last_registered_advance_count = 1
        self.advance_count += 1

    def register(self, res):
        self.last_registered_advance_count = res.advance_count
        self.advance_count += res.advance_count
        if res.error:
            self.error = res.error
        return res.node

    def success(self, node):
        self.node = node
        return self

    def failure(self, error):
        if not self.error or self.last_registered_advance_count == 0:
            self.error = error
        return self


#######################################
# PARSER
#######################################


class Parser:
    def __init__(self, tokens):
        self.tokens = tokens
        self.tok_idx = -1
        self.advance()

    def advance(
        self,
    ):
        self.tok_idx += 1
        if self.tok_idx < len(self.tokens):
            self.current_tok = self.tokens[self.tok_idx]
        return self.current_tok

    def parse(self):
        res = self.expr()
        if not res.error and self.current_tok.type != TT_EOF:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    "Expected '+', '-', '*', '/', '^', '==', '!=', '<', '>', <=', '>=', 'AND' or 'OR'",
                )
            )
        return res

    ###################################

    def expr(self):
        res = ParseResult()

        if self.current_tok.matches(TT_KEYWORD, "VAR"):
            res.register_advancement()
            self.advance()

            if self.current_tok.type != TT_IDENTIFIER:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        "Expected identifier",
                    )
                )

            var_name = self.current_tok
            res.register_advancement()
            self.advance()

            if self.current_tok.type != TT_EQ:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        "Expected '='",
                    )
                )

            res.register_advancement()
            self.advance()
            expr = res.register(self.expr())
            if res.error:
                return res
            return res.success(VarAssignNode(var_name, expr))

        node = res.register(
            self.bin_op(self.comp_expr, ((TT_KEYWORD, "AND"), (TT_KEYWORD, "OR")))
        )

        if res.error:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    "Expected 'VAR', 'IF', 'FOR', 'WHILE', 'FUN', int, float, identifier, '+', '-', '(' or 'NOT'",
                )
            )

        return res.success(node)

    def comp_expr(self):
        res = ParseResult()

        if self.current_tok.matches(TT_KEYWORD, "NOT"):
            op_tok = self.current_tok
            res.register_advancement()
            self.advance()

            node = res.register(self.comp_expr())
            if res.error:
                return res
            return res.success(UnaryOpNode(op_tok, node))

        node = res.register(
            self.bin_op(self.arith_expr, (TT_EE, TT_NE, TT_LT, TT_GT, TT_LTE, TT_GTE))
        )

        if res.error:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    "Expected int, float, identifier, '+', '-', '(' or 'NOT'",
                )
            )

        return res.success(node)

    def arith_expr(self):
        return self.bin_op(self.term, (TT_PLUS, TT_MINUS))

    def term(self):
        return self.bin_op(self.factor, (TT_MUL, TT_DIV))

    def factor(self):
        res = ParseResult()
        tok = self.current_tok

        if tok.type in (TT_PLUS, TT_MINUS):
            res.register_advancement()
            self.advance()
            factor = res.register(self.factor())
            if res.error:
                return res
            return res.success(UnaryOpNode(tok, factor))

        return self.power()

    def power(self):
        return self.bin_op(self.call, (TT_POW,), self.factor)

    def call(self):
        res = ParseResult()
        atom = res.register(self.atom())
        if res.error:
            return res

        if self.current_tok.type == TT_LPAREN:
            res.register_advancement()
            self.advance()
            arg_nodes = []

            if self.current_tok.type == TT_RPAREN:
                res.register_advancement()
                self.advance()
            else:
                arg_nodes.append(res.register(self.expr()))
                if res.error:
                    return res.failure(
                        InvalidSyntaxError(
                            self.current_tok.pos_start,
                            self.current_tok.pos_end,
                            "Expected ')', 'VAR', 'IF', 'FOR', 'WHILE', 'FUN', int, float, identifier, '+', '-', '(' or 'NOT'",
                        )
                    )

                while self.current_tok.type == TT_COMMA:
                    res.register_advancement()
                    self.advance()

                    arg_nodes.append(res.register(self.expr()))
                    if res.error:
                        return res

                if self.current_tok.type != TT_RPAREN:
                    return res.failure(
                        InvalidSyntaxError(
                            self.current_tok.pos_start,
                            self.current_tok.pos_end,
                            f"Expected ',' or ')'",
                        )
                    )

                res.register_advancement()
                self.advance()
            return res.success(CallNode(atom, arg_nodes))
        return res.success(atom)

    def atom(self):
        res = ParseResult()
        tok = self.current_tok

        if tok.type in (TT_INT, TT_FLOAT):
            res.register_advancement()
            self.advance()
            return res.success(NumberNode(tok))

        if tok.type in (TT_STRING):
            res.register_advancement()
            self.advance()
            return res.success(StringNode(tok))

        elif tok.type == TT_IDENTIFIER:
            res.register_advancement()
            self.advance()
            return res.success(VarAccessNode(tok))

        elif tok.type == TT_LPAREN:
            res.register_advancement()
            self.advance()
            expr = res.register(self.expr())
            if res.error:
                return res
            if self.current_tok.type == TT_RPAREN:
                res.register_advancement()
                self.advance()
                return res.success(expr)
            else:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        "Expected ')'",
                    )
                )

        elif tok.matches(TT_KEYWORD, "IF"):
            if_expr = res.register(self.if_expr())
            if res.error:
                return res
            return res.success(if_expr)

        elif tok.matches(TT_KEYWORD, "FOR"):
            for_expr = res.register(self.for_expr())
            if res.error:
                return res
            return res.success(for_expr)

        elif tok.matches(TT_KEYWORD, "WHILE"):
            while_expr = res.register(self.while_expr())
            if res.error:
                return res
            return res.success(while_expr)

        elif tok.matches(TT_KEYWORD, "FUN"):
            func_def = res.register(self.func_def())
            if res.error:
                return res
            return res.success(func_def)

        return res.failure(
            InvalidSyntaxError(
                tok.pos_start,
                tok.pos_end,
                "Expected int, float, identifier, '+', '-', '(', 'IF', 'FOR', 'WHILE', 'FUN'",
            )
        )

    def if_expr(self):
        res = ParseResult()
        cases = []
        else_case = None

        if not self.current_tok.matches(TT_KEYWORD, "IF"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'IF'",
                )
            )

        res.register_advancement()
        self.advance()

        condition = res.register(self.expr())
        if res.error:
            return res

        if not self.current_tok.matches(TT_KEYWORD, "THEN"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'THEN'",
                )
            )

        res.register_advancement()
        self.advance()

        expr = res.register(self.expr())
        if res.error:
            return res
        cases.append((condition, expr))

        while self.current_tok.matches(TT_KEYWORD, "ELIF"):
            res.register_advancement()
            self.advance()

            condition = res.register(self.expr())
            if res.error:
                return res

            if not self.current_tok.matches(TT_KEYWORD, "THEN"):
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        f"Expected 'THEN'",
                    )
                )

            res.register_advancement()
            self.advance()

            expr = res.register(self.expr())
            if res.error:
                return res
            cases.append((condition, expr))

        if self.current_tok.matches(TT_KEYWORD, "ELSE"):
            res.register_advancement()
            self.advance()

            else_case = res.register(self.expr())
            if res.error:
                return res

        return res.success(IfNode(cases, else_case))

    def for_expr(self):
        res = ParseResult()

        if not self.current_tok.matches(TT_KEYWORD, "FOR"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'FOR'",
                )
            )

        res.register_advancement()
        self.advance()

        if self.current_tok.type != TT_IDENTIFIER:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected identifier",
                )
            )

        var_name = self.current_tok
        res.register_advancement()
        self.advance()

        if self.current_tok.type != TT_EQ:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected '='",
                )
            )

        res.register_advancement()
        self.advance()

        start_value = res.register(self.expr())
        if res.error:
            return res

        if not self.current_tok.matches(TT_KEYWORD, "TO"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'TO'",
                )
            )

        res.register_advancement()
        self.advance()

        end_value = res.register(self.expr())
        if res.error:
            return res

        if self.current_tok.matches(TT_KEYWORD, "STEP"):
            res.register_advancement()
            self.advance()

            step_value = res.register(self.expr())
            if res.error:
                return res
        else:
            step_value = None

        if not self.current_tok.matches(TT_KEYWORD, "THEN"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'THEN'",
                )
            )

        res.register_advancement()
        self.advance()

        body = res.register(self.expr())
        if res.error:
            return res

        return res.success(ForNode(var_name, start_value, end_value, step_value, body))

    def while_expr(self):
        res = ParseResult()

        if not self.current_tok.matches(TT_KEYWORD, "WHILE"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'WHILE'",
                )
            )

        res.register_advancement()
        self.advance()

        condition = res.register(self.expr())
        if res.error:
            return res

        if not self.current_tok.matches(TT_KEYWORD, "THEN"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'THEN'",
                )
            )

        res.register_advancement()
        self.advance()

        body = res.register(self.expr())
        if res.error:
            return res

        return res.success(WhileNode(condition, body))

    def func_def(self):
        res = ParseResult()

        if not self.current_tok.matches(TT_KEYWORD, "FUN"):
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected 'FUN'",
                )
            )

        res.register_advancement()
        self.advance()

        if self.current_tok.type == TT_IDENTIFIER:
            var_name_tok = self.current_tok
            res.register_advancement()
            self.advance()
            if self.current_tok.type != TT_LPAREN:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        f"Expected '('",
                    )
                )
        else:
            var_name_tok = None
            if self.current_tok.type != TT_LPAREN:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        f"Expected identifier or '('",
                    )
                )

        res.register_advancement()
        self.advance()
        arg_name_toks = []

        if self.current_tok.type == TT_IDENTIFIER:
            arg_name_toks.append(self.current_tok)
            res.register_advancement()
            self.advance()

            while self.current_tok.type == TT_COMMA:
                res.register_advancement()
                self.advance()

                if self.current_tok.type != TT_IDENTIFIER:
                    return res.failure(
                        InvalidSyntaxError(
                            self.current_tok.pos_start,
                            self.current_tok.pos_end,
                            f"Expected identifier",
                        )
                    )

                arg_name_toks.append(self.current_tok)
                res.register_advancement()
                self.advance()

            if self.current_tok.type != TT_RPAREN:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        f"Expected ',' or ')'",
                    )
                )
        else:
            if self.current_tok.type != TT_RPAREN:
                return res.failure(
                    InvalidSyntaxError(
                        self.current_tok.pos_start,
                        self.current_tok.pos_end,
                        f"Expected identifier or ')'",
                    )
                )

        res.register_advancement()
        self.advance()

        if self.current_tok.type != TT_ARROW:
            return res.failure(
                InvalidSyntaxError(
                    self.current_tok.pos_start,
                    self.current_tok.pos_end,
                    f"Expected '->'",
                )
            )

        res.register_advancement()
        self.advance()
        node_to_return = res.register(self.expr())
        if res.error:
            return res

        return res.success(FuncDefNode(var_name_tok, arg_name_toks, node_to_return))

    ###################################

    def bin_op(self, func_a, ops, func_b=None):
        if func_b == None:
            func_b = func_a

        res = ParseResult()
        left = res.register(func_a())
        if res.error:
            return res

        while (
            self.current_tok.type in ops
            or (self.current_tok.type, self.current_tok.value) in ops
        ):
            op_tok = self.current_tok
            res.register_advancement()
            self.advance()
            right = res.register(func_b())
            if res.error:
                return res
            left = BinOpNode(left, op_tok, right)

        return res.success(left)


#######################################
# RUNTIME RESULT
#######################################


class RTResult:
    def __init__(self):
        self.value = None
        self.error = None

    def register(self, res):
        self.error = res.error
        return res.value

    def success(self, value):
        self.value = value
        return self

    def failure(self, error):
        self.error = error
        return self


#######################################
# VALUES
#######################################


class Value:
    def __init__(self):
        self.set_pos()
        self.set_context()

    def set_pos(self, pos_start=None, pos_end=None):
        self.pos_start = pos_start
        self.pos_end = pos_end
        return self

    def set_context(self, context=None):
        self.context = context
        return self

    def added_to(self, other):
        return None, self.illegal_operation(other)

    def subbed_by(self, other):
        return None, self.illegal_operation(other)

    def multed_by(self, other):
        return None, self.illegal_operation(other)

    def dived_by(self, other):
        return None, self.illegal_operation(other)

    def powed_by(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_eq(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_ne(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_lt(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_gt(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_lte(self, other):
        return None, self.illegal_operation(other)

    def get_comparison_gte(self, other):
        return None, self.illegal_operation(other)

    def anded_by(self, other):
        return None, self.illegal_operation(other)

    def ored_by(self, other):
        return None, self.illegal_operation(other)

    def notted(self):
        return None, self.illegal_operation(other)

    def execute(self, args):
        return RTResult().failure(self.illegal_operation())

    def copy(self):
        raise Exception("No copy method defined")

    def is_true(self):
        return False

    def illegal_operation(self, other=None):
        if not other:
            other = self
        return RTError(self.pos_start, other.pos_end, "Illegal operation", self.context)


class Number(Value):
    def __init__(self, value):
        super().__init__()
        self.value = value

    def added_to(self, other):
        if isinstance(other, Number):
            return Number(self.value + other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def subbed_by(self, other):
        if isinstance(other, Number):
            return Number(self.value - other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def multed_by(self, other):
        if isinstance(other, Number):
            return Number(self.value * other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def dived_by(self, other):
        if isinstance(other, Number):
            if other.value == 0:
                return None, RTError(
                    other.pos_start, other.pos_end, "Division by zero", self.context
                )

            return Number(self.value / other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def powed_by(self, other):
        if isinstance(other, Number):
            return Number(self.value**other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_eq(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value == other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_ne(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value != other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_lt(self, other):
        if isinstance(other, Number):
            return Number(int(self.value < other.value)).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_gt(self, other):
        if isinstance(other, Number):
            return Number(int(self.value > other.value)).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_lte(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value <= other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def get_comparison_gte(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value >= other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def anded_by(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value and other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def ored_by(self, other):
        if isinstance(other, Number):
            return (
                Number(int(self.value or other.value)).set_context(self.context),
                None,
            )
        else:
            return None, Value.illegal_operation(self, other)

    def notted(self):
        return Number(1 if self.value == 0 else 0).set_context(self.context), None

    def copy(self):
        copy = Number(self.value)
        copy.set_pos(self.pos_start, self.pos_end)
        copy.set_context(self.context)
        return copy

    def is_true(self):
        return self.value != 0

    def __repr__(self):
        return str(self.value)

class String(Value):
    def __init__(self, value):
        super().__init__()
        self.value = value
    
    def added_to(self, other):
        if isinstance(other, String):
            return String(self.value + other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)
    
    def multed_by(self, other):
        if isinstance(other, Number):
            return String(self.value * other.value).set_context(self.context), None
        else:
            return None, Value.illegal_operation(self, other)
    
    def is_true(self):
        return len(self.value) > 0
    
    def copy(self):
        copy = String(self.value)
        copy.set_pos(self.pos_start, self.pos_end)
        copy.set_context(self.context)
        return copy
    
    def __repr__(self):
        return f'"{self.value}"'

class Function(Value):
    def __init__(self, name, body_node, arg_names):
        super().__init__()
        self.name = name or "<anonymous>"
        self.body_node = body_node
        self.arg_names = arg_names

    def execute(self, args):
        res = RTResult()
        interpreter = Interpreter()
        new_context = Context(self.name, self.context, self.pos_start)
        new_context.symbol_table = SymbolTable(new_context.parent.symbol_table)

        if len(args) > len(self.arg_names):
            return res.failure(
                RTError(
                    self.pos_start,
                    self.pos_end,
                    f"{len(args) - len(self.arg_names)} too many args passed into '{self.name}'",
                    self.context,
                )
            )

        if len(args) < len(self.arg_names):
            return res.failure(
                RTError(
                    self.pos_start,
                    self.pos_end,
                    f"{len(self.arg_names) - len(args)} too few args passed into '{self.name}'",
                    self.context,
                )
            )

        for i in range(len(args)):
            arg_name = self.arg_names[i]
            arg_value = args[i]
            arg_value.set_context(new_context)
            new_context.symbol_table.set(arg_name, arg_value)

        value = res.register(interpreter.visit(self.body_node, new_context))
        if res.error:
            return res
        return res.success(value)

    def copy(self):
        copy = Function(self.name, self.body_node, self.arg_names)
        copy.set_context(self.context)
        copy.set_pos(self.pos_start, self.pos_end)
        return copy

    def __repr__(self):
        return f"<function {self.name}>"


#######################################
# CONTEXT
#######################################


class Context:
    def __init__(self, display_name, parent=None, parent_entry_pos=None):
        self.display_name = display_name
        self.parent = parent
        self.parent_entry_pos = parent_entry_pos
        self.symbol_table = None


#######################################
# SYMBOL TABLE
#######################################


class SymbolTable:
    def __init__(self, parent=None):
        self.symbols = {}
        self.parent = parent

    def get(self, name):
        value = self.symbols.get(name, None)
        if value == None and self.parent:
            return self.parent.get(name)
        return value

    def set(self, name, value):
        self.symbols[name] = value

    def remove(self, name):
        del self.symbols[name]


#######################################
# INTERPRETER
#######################################


class Interpreter:
    def visit(self, node, context):
        method_name = f"visit_{type(node).__name__}"
        method = getattr(self, method_name, self.no_visit_method)
        return method(node, context)

    def no_visit_method(self, node, context):
        raise Exception(f"No visit_{type(node).__name__} method defined")

    ###################################

    def visit_NumberNode(self, node, context):
        return RTResult().success(
            Number(node.tok.value)
            .set_context(context)
            .set_pos(node.pos_start, node.pos_end)
        )
    
    def visit_StringNode(self, node,  context):
        return RTResult().success(
            String(node.tok.value).set_context(context).set_pos(node.pos_start, node.pos_end)
        )

    def visit_VarAccessNode(self, node, context):
        res = RTResult()
        var_name = node.var_name_tok.value
        value = context.symbol_table.get(var_name)

        if not value:
            return res.failure(
                RTError(
                    node.pos_start,
                    node.pos_end,
                    f"'{var_name}' is not defined",
                    context,
                )
            )

        value = value.copy().set_pos(node.pos_start, node.pos_end)
        return res.success(value)

    def visit_VarAssignNode(self, node, context):
        res = RTResult()
        var_name = node.var_name_tok.value
        value = res.register(self.visit(node.value_node, context))
        if res.error:
            return res

        context.symbol_table.set(var_name, value)
        return res.success(value)

    def visit_BinOpNode(self, node, context):
        res = RTResult()
        left = res.register(self.visit(node.left_node, context))
        if res.error:
            return res
        right = res.register(self.visit(node.right_node, context))
        if res.error:
            return res

        if node.op_tok.type == TT_PLUS:
            result, error = left.added_to(right)
        elif node.op_tok.type == TT_MINUS:
            result, error = left.subbed_by(right)
        elif node.op_tok.type == TT_MUL:
            result, error = left.multed_by(right)
        elif node.op_tok.type == TT_DIV:
            result, error = left.dived_by(right)
        elif node.op_tok.type == TT_POW:
            result, error = left.powed_by(right)
        elif node.op_tok.type == TT_EE:
            result, error = left.get_comparison_eq(right)
        elif node.op_tok.type == TT_NE:
            result, error = left.get_comparison_ne(right)
        elif node.op_tok.type == TT_LT:
            result, error = left.get_comparison_lt(right)
        elif node.op_tok.type == TT_GT:
            result, error = left.get_comparison_gt(right)
        elif node.op_tok.type == TT_LTE:
            result, error = left.get_comparison_lte(right)
        elif node.op_tok.type == TT_GTE:
            result, error = left.get_comparison_gte(right)
        elif node.op_tok.matches(TT_KEYWORD, "AND"):
            result, error = left.anded_by(right)
        elif node.op_tok.matches(TT_KEYWORD, "OR"):
            result, error = left.ored_by(right)

        if error:
            return res.failure(error)
        else:
            return res.success(result.set_pos(node.pos_start, node.pos_end))

    def visit_UnaryOpNode(self, node, context):
        res = RTResult()
        number = res.register(self.visit(node.node, context))
        if res.error:
            return res

        error = None

        if node.op_tok.type == TT_MINUS:
            number, error = number.multed_by(Number(-1))
        elif node.op_tok.matches(TT_KEYWORD, "NOT"):
            number, error = number.notted()

        if error:
            return res.failure(error)
        else:
            return res.success(number.set_pos(node.pos_start, node.pos_end))

    def visit_IfNode(self, node, context):
        res = RTResult()

        for condition, expr in node.cases:
            condition_value = res.register(self.visit(condition, context))
            if res.error:
                return res

            if condition_value.is_true():
                expr_value = res.register(self.visit(expr, context))
                if res.error:
                    return res
                return res.success(expr_value)

        if node.else_case:
            else_value = res.register(self.visit(node.else_case, context))
            if res.error:
                return res
            return res.success(else_value)

        return res.success(None)

    def visit_ForNode(self, node, context):
        res = RTResult()

        start_value = res.register(self.visit(node.start_value_node, context))
        if res.error:
            return res

        end_value = res.register(self.visit(node.end_value_node, context))
        if res.error:
            return res

        if node.step_value_node:
            step_value = res.register(self.visit(node.step_value_node, context))
            if res.error:
                return res
        else:
            step_value = Number(1)

        i = start_value.value

        if step_value.value >= 0:
            condition = lambda: i < end_value.value
        else:
            condition = lambda: i > end_value.value

        while condition():
            context.symbol_table.set(node.var_name_tok.value, Number(i))
            i += step_value.value

            res.register(self.visit(node.body_node, context))
            if res.error:
                return res

        return res.success(None)

    def visit_WhileNode(self, node, context):
        res = RTResult()

        while True:
            condition = res.register(self.visit(node.condition_node, context))
            if res.error:
                return res

            if not condition.is_true():
                break

            res.register(self.visit(node.body_node, context))
            if res.error:
                return res

        return res.success(None)

    def visit_FuncDefNode(self, node, context):
        res = RTResult()

        func_name = node.var_name_tok.value if node.var_name_tok else None
        body_node = node.body_node
        arg_names = [arg_name.value for arg_name in node.arg_name_toks]
        func_value = (
            Function(func_name, body_node, arg_names)
            .set_context(context)
            .set_pos(node.pos_start, node.pos_end)
        )

        if node.var_name_tok:
            context.symbol_table.set(func_name, func_value)

        return res.success(func_value)

    def visit_CallNode(self, node, context):
        res = RTResult()
        args = []

        value_to_call = res.register(self.visit(node.node_to_call, context))
        if res.error:
            return res
        value_to_call = value_to_call.copy().set_pos(node.pos_start, node.pos_end)

        for arg_node in node.arg_nodes:
            args.append(res.register(self.visit(arg_node, context)))
            if res.error:
                return res

        return_value = res.register(value_to_call.execute(args))
        if res.error:
            return res
        return res.success(return_value)


#######################################
# RUN
#######################################

global_symbol_table = SymbolTable()
global_symbol_table.set("NULL", Number(0))
global_symbol_table.set("FALSE", Number(0))
global_symbol_table.set("TRUE", Number(1))


def run(fn, text):
    # Generate tokens
    lexer = Lexer(fn, text)
    tokens, error = lexer.make_tokens()
    if error:
        return None, error

    # Generate AST
    parser = Parser(tokens)
    ast = parser.parse()
    if ast.error:
        return None, ast.error

    # Run program
    interpreter = Interpreter()
    context = Context("<program>")
    context.symbol_table = global_symbol_table
    result = interpreter.visit(ast.node, context)


    return result.value, result.error