DeCarabas/lrparsers
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The start rule cannot be transparent

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This commit is contained in:
John Doty 2024-09-09 06:23:11 -07:00
parent 49b76b9bcc
commit 0cbf696303
1 changed files with 5 additions and 1 deletions
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6
parser/parser.py
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@ -2815,10 +2815,12 @@ class Grammar:
def get_precedence(self, name: str) -> None | tuple[Assoc, int]: def get_precedence(self, name: str) -> None | tuple[Assoc, int]:
return self._precedence.get(name) return self._precedence.get(name)
# TODO: The flattened form should retain NonTerminal, not just str.
def generate_nonterminal_dict( def generate_nonterminal_dict(
self, start: str | None = None self, start: str | None = None
) -> typing.Tuple[dict[str, list[list[str | Terminal]]], set[str]]: ) -> typing.Tuple[dict[str, list[list[str | Terminal]]], set[str]]:
"""Convert the rules into a dictionary of productions. """Convert the rules into a dictionary of productions, and a set of
the names of transparent nonterminals.
Our table generators work on a very flat set of productions. This is the Our table generators work on a very flat set of productions. This is the
first step in flattening the productions from the members: walk the rules first step in flattening the productions from the members: walk the rules
@ -2838,6 +2840,8 @@ class Grammar:
rule = nonterminals.get(start) rule = nonterminals.get(start)
if rule is None: if rule is None:
raise ValueError(f"Cannot find a rule named '{start}'") raise ValueError(f"Cannot find a rule named '{start}'")
if rule.transparent:
raise ValueError("The start rule cannot be transparent")
queue = [rule] queue = [rule]
while len(queue) > 0: while len(queue) > 0:
rule = queue.pop() rule = queue.pop()