110 lines
2.7 KiB
Python
110 lines
2.7 KiB
Python
from dataclasses import dataclass
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from typing import Any
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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: Any
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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: Any
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right: Any
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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: Any
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def __repr__(self):
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return f"Unary({self.op!r}, {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 and tok.kind != kind:
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raise ParseError(f"expected {kind}, 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):
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node = self._expr()
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tok = self._peek()
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if tok.kind != 'EOF':
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raise ParseError(f"unexpected token {tok.kind!r} ({tok.value!r})")
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return node
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def _expr(self):
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# expr → term (('+' | '-') term)*
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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):
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# term → unary (('*' | '/') unary)*
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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):
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# unary → '-' unary | primary
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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):
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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('LPAREN')
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node = self._expr()
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self._consume('RPAREN')
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return node
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if tok.kind == 'EOF':
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raise ParseError("unexpected end of input")
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raise ParseError(f"unexpected token {tok.kind!r} ({tok.value!r})")
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def parse(tokens) -> Any:
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"""Parse a token list from calc.lexer.tokenize into an AST.
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AST node types:
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Num(value) — numeric literal
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BinOp(op, left, right) — binary operation; op in {'+','-','*','/'}
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Unary(op, operand) — unary minus; op == '-'
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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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