115 lines
2.9 KiB
Python
115 lines
2.9 KiB
Python
from dataclasses import dataclass
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from typing import Union
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from calc.lexer import Token
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class ParseError(Exception):
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pass
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@dataclass
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class Num:
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value: Union[int, float]
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def __repr__(self):
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return f"Num({self.value!r})"
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@dataclass
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class BinOp:
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op: str
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left: 'Node'
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right: 'Node'
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def __repr__(self):
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return f"BinOp({self.op!r}, {self.left!r}, {self.right!r})"
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@dataclass
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class Unary:
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op: str
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operand: 'Node'
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def __repr__(self):
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return f"Unary({self.op!r}, {self.operand!r})"
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Node = Union[Num, BinOp, Unary]
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class _Parser:
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def __init__(self, tokens: list):
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self._tokens = tokens
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self._pos = 0
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def _peek(self) -> Token:
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return self._tokens[self._pos]
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def _consume(self, kind: str = None) -> Token:
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tok = self._tokens[self._pos]
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if kind and tok.kind != kind:
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raise ParseError(f"expected {kind!r}, got {tok.kind!r} ({tok.value!r})")
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self._pos += 1
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return tok
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def parse(self) -> Node:
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if self._peek().kind == 'EOF':
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raise ParseError("empty expression")
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node = self._expr()
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if self._peek().kind != 'EOF':
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raise ParseError(
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f"unexpected token {self._peek().kind!r} ({self._peek().value!r})"
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)
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return node
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def _expr(self) -> Node:
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node = self._term()
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while self._peek().kind in ('PLUS', 'MINUS'):
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op = self._consume().value
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right = self._term()
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node = BinOp(op, node, right)
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return node
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def _term(self) -> Node:
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node = self._unary()
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while self._peek().kind in ('STAR', 'SLASH'):
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op = self._consume().value
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right = self._unary()
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node = BinOp(op, node, right)
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return node
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def _unary(self) -> Node:
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if self._peek().kind == 'MINUS':
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op = self._consume().value
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operand = self._unary()
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return Unary(op, operand)
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return self._primary()
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def _primary(self) -> Node:
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tok = self._peek()
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if tok.kind == 'NUMBER':
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self._consume()
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return Num(tok.value)
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if tok.kind == 'LPAREN':
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self._consume()
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node = self._expr()
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if self._peek().kind != 'RPAREN':
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raise ParseError(
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f"expected ')' but got {self._peek().kind!r} ({self._peek().value!r})"
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)
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self._consume()
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return node
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if tok.kind == 'EOF':
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raise ParseError("unexpected end of expression")
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raise ParseError(f"unexpected token {tok.kind!r} ({tok.value!r})")
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def parse(tokens: list) -> Node:
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"""Parse a token list from calc.lexer.tokenize() into an AST.
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Returns one of: Num(value), BinOp(op, left, right), Unary(op, operand).
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Raises ParseError on malformed input.
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"""
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return _Parser(tokens).parse()
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