63 lines
1.3 KiB
Python
63 lines
1.3 KiB
Python
from dataclasses import dataclass
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from typing import Union
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class LexError(Exception):
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pass
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@dataclass
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class Token:
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kind: str
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value: Union[int, float, str, None]
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def __repr__(self):
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return f"{self.kind}({self.value!r})"
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_SINGLE = {
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'+': 'PLUS',
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'-': 'MINUS',
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'*': 'STAR',
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'/': 'SLASH',
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'(': 'LPAREN',
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')': 'RPAREN',
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}
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def tokenize(src: str) -> list:
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tokens = []
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i = 0
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while i < len(src):
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ch = src[i]
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if ch in ' \t':
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i += 1
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continue
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if ch in _SINGLE:
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tokens.append(Token(_SINGLE[ch], ch))
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i += 1
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continue
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if ch.isdigit() or ch == '.':
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j = i
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has_dot = False
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while j < len(src) and (src[j].isdigit() or (src[j] == '.' and not has_dot)):
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if src[j] == '.':
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has_dot = True
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j += 1
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raw = src[i:j]
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try:
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value = float(raw) if has_dot else int(raw)
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except ValueError:
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raise LexError(f"unexpected character '.' at position {i}")
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tokens.append(Token('NUMBER', value))
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i = j
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continue
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raise LexError(f"unexpected character {ch!r} at position {i}")
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tokens.append(Token('EOF', None))
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return tokens
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