sane-date-math: convert to LR parser
This commit is contained in:
parent
51a96525d9
commit
16fa1e0eda
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@ -2,8 +2,8 @@
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# i just went overboard playing around with parsers, is all.
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# use this like `./sane-date-math 'today - 5d'`
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# of course, it handles parenthesizes and operator precedence, so you can do sillier things like
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# `./sane-date-math ' today - (3*4+1 - ((0)) ) *7d '`
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# of course, it handles parentheses and operator precedence/associativity, so you can do sillier things like
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# `./sane-date-math ' today - (1+3 *4 - ((0)) ) *7d '`
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import abc
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@ -15,8 +15,6 @@ class Token:
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self.c = c
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def __repr__(self) -> str:
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if self == EOF:
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return "<EOF>"
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return f"{self.c!r}"
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def __str__(self) -> str:
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@ -25,7 +23,6 @@ class Token:
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def __eq__(self, other: 'Token') -> bool:
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return self.c == other.c
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EOF = Token('\x05')
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PLUS = Token('+')
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MINUS = Token('-')
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ASTERISK = Token('*')
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@ -40,349 +37,235 @@ ALPHA = ALPHA_LOWER + ALPHA_UPPER
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ALPHA_UNDER = ALPHA + [UNDERSCORE]
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ALPHA_NUM_UNDER = ALPHA_UNDER + DIGITS
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class ParserContext:
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def feed(self, token: Token) -> 'ParserContext':
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return None # can't ingest the token
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def upgrade(self) -> 'ParserContext':
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return None # no upgrade path
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# TODO: should be enum
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class ParseCode:
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# return if the parser cannot parse the provided token
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HALT = 0
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# return if the parser is already "complete" and the token should be yielded to the outer context instead
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YIELD = 1
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# return is the parser successfully consumed the provided token and parsing should continue
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CONTINUE = 2
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class ParserContext(metaclass=abc.ABCMeta):
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@abc.abstractmethod
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def feed(self, token: Token) -> ParseCode:
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"""
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possibly ingests this token, modifying internal state,
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and providing instruction to the outer parser layer on
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how to proceed.
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"""
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pass
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def context(self) -> 'ParserContext':
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"""
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hack to make type-level "Productions" compatible with instance-level "ParserContext"s.
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"""
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return self
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def destructure(self) -> object:
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"""
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destructure the outer layer of this ParserContext to obtain access to whatever state it captured.
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e.g. Then([A, Choice([B, C])]) destructures first to [A, Choice([B, C])].
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it's not recursive; the inner layers must be manually destructured.
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"""
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return self
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class Then(ParserContext):
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class Parser:
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"""
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primitive combinator: given a sequence of parser constructs, parse the input
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using the first parser until that parser yields, then parse using the second
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parser, and so on.
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LR parser.
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keeps exactly one root item, and for each input token
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feeds it to the root, possibly "upgrading" the root N times
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before it's able to be fed.
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"""
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def __init__(self, items: list):
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self.items = [i.context() for i in items]
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def __init__(self, root: ParserContext):
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self.root = root
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def feed(self, token: Token) -> bool:
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new_root = self.root.feed(token)
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if new_root is not None:
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self.root = new_root
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return True
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else:
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# root can't directly accept this item.
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# "upgrade" it and try again.
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new_root = self.root.upgrade()
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if new_root is None: return False
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self.root = new_root
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return self.feed(token)
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def complete(self) -> ParserContext:
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# upgrade the root as far as possible before returning
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root = None
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new_root = self.root
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while new_root is not None:
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root = new_root
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new_root = root.upgrade()
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return root
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class ReprParserContext(ParserContext):
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""" helper that gives a good default repr to most contexts """
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def __init__(self, items: list = None):
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self.items = items if items is not None else []
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def __repr__(self) -> str:
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return f"Then({self.items!r})"
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return f'{self.__class__.__name__}({self.items!r})'
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def __str__(self) -> str:
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return str(self.items)
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def feed(self, token: Token) -> ParseCode:
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# we expect parser contexts to be fused: once they YIELD,
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# they should yield on all future calls as well
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for i in self.items:
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result = i.feed(token)
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if result != ParseCode.YIELD: return result
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else:
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# all items are done parsing; so are we!
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return ParseCode.YIELD
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class BaseContext(ReprParserContext):
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""" empty context; initial state of the parser """
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def feed(self, token: Token) -> ParserContext:
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if token == SPACE:
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return self
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if token == OPEN_PAREN:
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return ParenContext(BaseContext())
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if token in DIGITS:
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return IntegerContext([token])
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if token in ALPHA_UNDER:
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return IdentifierContext([token])
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def destructure(self) -> list:
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return self.items
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class IdentifierContext(ReprParserContext):
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""" context is an identifier like `today` """
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def __init__(self, tokens: list):
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super().__init__(tokens)
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self.tokens = tokens
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class Choice(ParserContext):
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def feed(self, token: Token) -> ParserContext:
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if token in ALPHA_NUM_UNDER:
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return IdentifierContext(self.tokens + [token])
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def upgrade(self) -> ParserContext:
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return StrongValueContext(self)
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class IntegerContext(ReprParserContext):
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""" context is an integer like `45` """
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def __init__(self, tokens: list):
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super().__init__(tokens)
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self.tokens = tokens
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def feed(self, token: Token) -> ParserContext:
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if token in DIGITS:
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return IntegerContext(self.tokens + [token])
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if token == Token('d'):
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return DurationContext(self)
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def upgrade(self) -> ParserContext:
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# can't continue the integer; it becomes a value
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return StrongValueContext(self)
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class DurationContext(ReprParserContext):
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""" context is a duration like `14d` """
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def __init__(self, value: IntegerContext):
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super().__init__([value])
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self.value = value
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def upgrade(self) -> ParserContext:
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return StrongValueContext(self)
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class BaseValueContext(ReprParserContext):
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""" abstract base for types that can be used in compound expressions """
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def __init__(self, value: ParserContext):
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super().__init__([value])
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self.value = value
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def feed(self, token: Token) -> ParserContext:
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if token == SPACE:
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return self
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class StrongValueContext(BaseValueContext):
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"""
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primitive combinator: try each parser in order and use the first match.
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NB: there's no lookahead. whichever parser is able to parse the first token
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is used for the entire stream.
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in the context of operators, a strong value is something which prefers
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to not be grabbed by a lhs value.
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so for example, strong values have the opportunity to initiate a multiply operation before the lhs closes an addition operation that this strong value is a part of
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"""
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def __init__(self, choices: list):
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self.choices = choices
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self.active = None
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def feed(self, token: Token) -> ParserContext:
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if token == ASTERISK:
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return BinaryOpContext(self, token, BaseContext())
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return super().feed(token)
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def __repr__(self) -> str:
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return f"Choice({self.choices!r})"
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def upgrade(self) -> ParserContext:
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return WeakValueContext(self.value)
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def __str__(self) -> str:
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if self.active is not None:
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return str(self.active)
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else:
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return repr(self)
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class WeakValueContext(BaseValueContext):
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def feed(self, token: Token) -> ParserContext:
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if token == PLUS:
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return BinaryOpContext(self, token, BaseContext())
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if token == MINUS:
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return BinaryOpContext(self, token, BaseContext())
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def feed(self, token: Token) -> ParseCode:
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if self.active is not None:
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return self.active.feed(token)
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return super().feed(token)
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for choice in self.choices:
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item = choice.context()
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result = item.feed(token)
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if result is not ParseCode.HALT:
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self.active = item
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return result
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class BinaryOpContext(ReprParserContext):
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""" context for a binary operation. the LHS and operator are parsed, but the rhs may not yet contain a value """
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def __init__(self, lhs: BaseValueContext, oper: Token, rhs: ParserContext):
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super().__init__([lhs, oper, rhs])
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self.lhs = lhs
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self.oper = oper
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self.rhs = rhs
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return ParseCode.HALT # no matches
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@property
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def precedence_class(self) -> type:
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if self.oper in [PLUS, MINUS]:
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return WeakValueContext
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if self.oper == ASTERISK:
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return StrongValueContext
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def destructure(self) -> ParserContext:
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return self.active
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def feed(self, token: Token) -> ParserContext:
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new_rhs = self.rhs.feed(token)
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if new_rhs is not None:
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return BinaryOpContext(self.lhs, self.oper, new_rhs)
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class WantToken(ParserContext):
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"""
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match a single token out of a list of valid tokens
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"""
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def __init__(self, want: list):
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self.has = None
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self.want = [want] if isinstance(want, Token) else want
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def upgrade(self) -> ParserContext:
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new_rhs = self.rhs.upgrade()
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if new_rhs is None: return None
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def __repr__(self) -> str:
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return f"WantToken({self.want!r})"
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# upgrade self once the rhs has reach the required precedence compatible with this operator
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new_self = BinaryOpContext(self.lhs, self.oper, new_rhs)
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if isinstance(new_rhs, self.precedence_class):
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return StrongValueContext(self) # close the operation
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def feed(self, token: Token) -> ParseCode:
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if self.has is not None: return ParseCode.YIELD
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if token in self.want:
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self.has = token
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return ParseCode.CONTINUE
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return ParseCode.HALT
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return new_self
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def destructure(self) -> Token:
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return self.has
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class ParenContext(ReprParserContext):
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""" context for a value contained within parentheses """
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def __init__(self, inner: ParserContext):
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super().__init__([inner])
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self.inner = inner
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class Empty(ParserContext):
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"""
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used as a terminal to allow for constructs like `optional`
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"""
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def feed(self, token: Token) -> ParseCode:
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return ParseCode.YIELD
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def feed(self, token: Token) -> ParserContext:
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new_inner = self.inner.feed(token)
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if new_inner is not None:
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return ParenContext(new_inner)
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def destructure(self) -> None:
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return None
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if token == CLOSE_PAREN and isinstance(self.inner, WeakValueContext):
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return StrongValueContext(self)
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def optional(context: ParserContext) -> ParserContext:
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return Choice([context, Empty()])
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def upgrade(self) -> ParserContext:
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new_inner = self.inner.upgrade()
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if new_inner is not None:
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return ParenContext(new_inner)
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## "Productions" sit on top of these base ParserContexts in order to give names to
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## large token sequences and to "reduce" them into AST types more intelligently.
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class ProductionContext(ParserContext):
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"""
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this adapts from the Production system of specification to the ParserContext system.
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this is instantiated for high-level productions where we specify a grammar
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and then parse "all in one go", sealing away incomplete state, and converting
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the parsed tokens into actually useful abstractions (like signed numbers).
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"""
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def __init__(self, production: 'Production', context: ParserContext = None):
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self.production = production
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self.context = context if context is not None else production.grammar()
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def __repr__(self) -> str:
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return f"ProductionContext({self.production!r}, {self.context!r})"
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def __str__(self) -> str:
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return str(self.context)
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def feed(self, token: Token) -> ParseCode:
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return self.context.feed(token)
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def reduce_inner(self, inner: ParserContext):
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if isinstance(inner, ProductionContext):
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return inner.reduce() # easy
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elif isinstance(inner, ParserContext):
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return self.reduce_inner(inner.destructure())
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elif isinstance(inner, list): # happens via unpacking of Then objects
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return [self.reduce_inner(i) for i in inner]
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else:
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return inner
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def reduce(self) -> object:
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# XXX this ends up being a leaf -> root reduction,
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# which generally makes it harder to achieve detailed control when nesting.
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return self.production.reduce(self.reduce_inner(self.context))
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class Production:
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"""
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non-generic, likely multi-token productions,
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specified in terms of other Productions and the above primitives
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"""
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def grammar(self) -> ParserContext:
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raise NotImplementedError()
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def context(self) -> ParserContext:
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return ProductionContext(self)
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def reduce(self, inner: object) -> object:
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"""
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use to construct the outer types out of already-converted inner types.
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e.g. Number = Then([optional(Minus), Digits, optional(Suffix)])
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gets called with reduce([a, b, c]), where a is the already reduced `optional(Minus)`,
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i.e. `None` or whatever type corresponds to the Minus token.
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"""
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return inner
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class DigitProduction(Production):
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""" one digit token """
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def grammar(self) -> ParserContext:
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return WantToken(DIGITS)
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def reduce(self, inner: Token) -> int:
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return int(inner.c)
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class IntProduction(Production):
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""" multi-digit integer """
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def grammar(self) -> ParserContext:
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return Then([
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DigitProduction(),
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optional(IntProduction()),
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])
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def reduce(self, inner: list) -> int:
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# TODO: wrong associativity
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leading, trailing = inner
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if trailing is None:
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return leading
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else:
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return leading*10 + trailing
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class DurationOrIntProduction(Production):
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# due to a lack of lookahead, we combine duration and int parsing into one production
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# because a duration shares a complete int as prefix
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def grammar(self) -> ParserContext:
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return Then([
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IntProduction(),
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optional(WantToken(Token('d'))),
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])
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def reduce(self, inner: list) -> 'Literal':
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value, suffix = inner
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if suffix is None:
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return Literal(value)
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else:
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return Literal(timedelta(value))
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class Whitespace(Production):
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def grammar(self) -> ParserContext:
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return Then([
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WantToken(SPACE),
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optional(Whitespace()),
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])
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class ParenthesizedExpr(Production):
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def grammar(self) -> ParserContext:
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return Then([
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WantToken(OPEN_PAREN),
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Expr(),
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WantToken(CLOSE_PAREN),
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])
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def reduce(self, inner: list) -> 'AstItem':
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open, expr, close = inner
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return expr
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class IdentifierTail(Production):
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def grammar(self) -> ParserContext:
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return Then([
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WantToken(ALPHA_NUM_UNDER),
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optional(IdentifierTail()),
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])
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class Identifier(Production):
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""" variable-style identifier, e.g. 'TODAY' """
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def grammar(self) -> ParserContext:
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return Then([
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WantToken(ALPHA_UNDER),
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optional(IdentifierTail()),
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])
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def reduce(self, inner: list) -> 'Literal':
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# fold the tokens into a string
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first, rest = inner
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head = first.c
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while rest is not None:
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next, rest = rest
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head += next.c
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return Variable(head)
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class UnaryExpr(Production):
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""" some expression which does not invoke any operators at the outermost level """
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def grammar(self) -> ParserContext:
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return Then([
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optional(Whitespace()),
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Choice([
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DurationOrIntProduction(),
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Identifier(),
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ParenthesizedExpr(),
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]),
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optional(Whitespace()),
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])
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def reduce(self, inner: list):
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# drop the whitespace
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leading, primary, trailing = inner
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return primary
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class ExprRHS(Production):
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""" right hand side of a binary operation """
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def grammar(self) -> ParserContext:
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return Then([
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Choice([WantToken(ASTERISK), WantToken(PLUS), WantToken(MINUS)]),
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# remaining, is just another `Expr`, but we need to keep the fields expanded here to control precedence.
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UnaryExpr(),
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Choice([ExprRHS(), Empty()]),
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])
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class Expr(Production):
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""" this is the top-level production """
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def grammar(self) -> ParserContext:
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return Then([
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UnaryExpr(),
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Choice([ExprRHS(), Empty()])
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])
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def reduce(self, inner: list):
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||||
lhs, rhs = inner
|
||||
if rhs is None: return lhs
|
||||
|
||||
# convert the whole right-hand-side of the tree, iteratively.
|
||||
oper, rhs, rhs_next = rhs
|
||||
if oper == ASTERISK:
|
||||
# multiplication has high precedence and we grab the adjacent token ASAP
|
||||
lhs = MulOp(lhs, rhs)
|
||||
if rhs_next is not None:
|
||||
lhs = self.reduce([lhs, rhs_next])
|
||||
else:
|
||||
# reduce the rhs and *then* apply this operator
|
||||
if rhs_next is not None:
|
||||
rhs = self.reduce([rhs, rhs_next])
|
||||
|
||||
if oper == PLUS:
|
||||
lhs = AddOp(lhs, rhs)
|
||||
elif oper == MINUS:
|
||||
lhs = SubOp(lhs, rhs)
|
||||
|
||||
return lhs
|
||||
|
||||
|
||||
## parsed productions are `reduce`d to more useful `AstItem` items which we use
|
||||
## for the actual evaluation/computation
|
||||
## AstItems are produced from a ParserContext input
|
||||
## ParserContext parse outputs are translated into `AstItem`s before evaluation
|
||||
## so that we can operate on a higher-level tree that directly encodes native values like integers
|
||||
|
||||
class AstItem(metaclass=abc.ABCMeta):
|
||||
@abc.abstractmethod
|
||||
def eval(self, context: dict):
|
||||
pass
|
||||
|
||||
@staticmethod
|
||||
def decode_item(p: ParserContext) -> 'AstItem':
|
||||
if isinstance(p, IntegerContext):
|
||||
return Literal(AstItem.decode_integer(p))
|
||||
if isinstance(p, DurationContext):
|
||||
return Literal(timedelta(AstItem.decode_integer(p.value)))
|
||||
if isinstance(p, IdentifierContext):
|
||||
return Variable(AstItem.decode_identifier(p))
|
||||
if isinstance(p, BaseValueContext):
|
||||
return AstItem.decode_item(p.value)
|
||||
if isinstance(p, BinaryOpContext):
|
||||
return AstItem.decode_bin_op(
|
||||
p.oper.c,
|
||||
AstItem.decode_item(p.lhs),
|
||||
AstItem.decode_item(p.rhs)
|
||||
)
|
||||
if isinstance(p, ParenContext):
|
||||
return AstItem.decode_item(p.inner)
|
||||
|
||||
@staticmethod
|
||||
def decode_integer(p: IntegerContext) -> int:
|
||||
return int(''.join(t.c for t in p.tokens))
|
||||
|
||||
@staticmethod
|
||||
def decode_identifier(p: IdentifierContext) -> str:
|
||||
return ''.join(t.c for t in p.tokens)
|
||||
|
||||
@staticmethod
|
||||
def decode_bin_op(ty: str, lhs: 'AstItem', rhs: 'AstItem') -> 'BinaryOp':
|
||||
if ty == '+':
|
||||
return AddOp(lhs, rhs)
|
||||
if ty == '-':
|
||||
return SubOp(lhs, rhs)
|
||||
if ty == '*':
|
||||
return MulOp(lhs, rhs)
|
||||
|
||||
class Literal(AstItem):
|
||||
def __init__(self, v):
|
||||
self.v = v
|
||||
|
|
@ -429,32 +312,33 @@ class MulOp(BinaryOp):
|
|||
def eval(self, context: dict):
|
||||
return self.lhs.eval(context) * self.rhs.eval(context)
|
||||
|
||||
|
||||
## toplevel routine. tokenize -> parse -> decode to AST -> evaluate
|
||||
|
||||
def tokenize(stream: str) -> list:
|
||||
return [Token(char) for char in stream]
|
||||
|
||||
def parse(ty: Production, tokens: list) -> AstItem:
|
||||
ctx = Then([ty, Empty()])
|
||||
def parse(tokens: list) -> ParserContext:
|
||||
parser = Parser(BaseContext())
|
||||
for i, t in enumerate(tokens):
|
||||
result = ctx.feed(t)
|
||||
result = parser.feed(t)
|
||||
# print(f"i={i}; t={t}; state: {ctx!r}")
|
||||
assert result == ParseCode.CONTINUE, f"unexpected token '{t}' at {i}; state: {ctx!r}"
|
||||
assert result, f"unexpected token '{t}' at {i}; state: {parser.complete()!r}"
|
||||
|
||||
# feed a trailing EOF which no production should consume.
|
||||
# this either drives the context to a HALT state, if it's expecting
|
||||
# some specific other token, or YIELD if it's happy for the stream to be closed.
|
||||
assert ctx.feed(EOF) == ParseCode.YIELD, f"incomplete expression: {ctx!r}"
|
||||
|
||||
return ctx.destructure()[0].reduce()
|
||||
return parser.complete()
|
||||
|
||||
|
||||
def evaluate(expr: str) -> object:
|
||||
tok = tokenize(expr)
|
||||
expr = parse(Expr(), tok)
|
||||
print(expr)
|
||||
parse_tree = parse(tok)
|
||||
print(parse_tree)
|
||||
ast = AstItem.decode_item(parse_tree)
|
||||
print(ast)
|
||||
|
||||
env = dict(
|
||||
today=datetime.now()
|
||||
)
|
||||
return expr.eval(env)
|
||||
return ast.eval(env)
|
||||
|
||||
|
||||
if __name__ == '__main__':
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user