105 lines
2.6 KiB
Python
105 lines
2.6 KiB
Python
from dataclasses import dataclass
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from typing import Union
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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})"
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@dataclass
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class BinOp:
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op: str
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left: object
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right: object
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def __repr__(self):
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return f"BinOp({self.op}, {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: object
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def __repr__(self):
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return f"Unary({self.op}, {self.operand!r})"
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class _Parser:
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def __init__(self, tokens):
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self.tokens = tokens
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self.pos = 0
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def _peek(self):
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return self.tokens[self.pos]
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def _consume(self, kind=None):
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tok = self.tokens[self.pos]
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if kind is not None and tok.kind != kind:
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raise ParseError(f"expected {kind!r}, got {tok.kind!r}")
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self.pos += 1
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return tok
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def _expr(self):
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left = self._term()
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while self._peek().kind in ('PLUS', 'MINUS'):
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op = self._consume().kind
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right = self._term()
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left = BinOp(op, left, right)
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return left
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def _term(self):
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left = self._unary()
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while self._peek().kind in ('STAR', 'SLASH'):
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op = self._consume().kind
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right = self._unary()
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left = BinOp(op, left, right)
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return left
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def _unary(self):
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if self._peek().kind == 'MINUS':
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self._consume()
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return Unary('MINUS', self._unary())
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return self._primary()
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def _primary(self):
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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(f"expected ')', got {self._peek().kind!r}")
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self._consume()
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return node
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raise ParseError(f"unexpected token {tok.kind!r}")
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def parse(tokens) -> object:
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"""Parse a token list into an AST.
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Nodes:
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Num(value) — numeric literal (int or float)
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BinOp(op, left, right) — binary op; op in {'PLUS','MINUS','STAR','SLASH'}
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Unary(op, operand) — unary minus; op == 'MINUS'
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Raises ParseError on malformed input.
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"""
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p = _Parser(tokens)
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if p._peek().kind == 'EOF':
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raise ParseError("empty input")
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node = p._expr()
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if p._peek().kind != 'EOF':
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raise ParseError(f"unexpected token {p._peek().kind!r} after expression")
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return node
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