def _lex_rhs(stream: TokenStream, gram: Grammar) -> _Literal:
"""FIXME: How should we define lexical productions?"""
token = stream.take()
if token.kind == TokenCat.STRING or token.kind == TokenCat.NUMBER:
return gram.literal(token.value)
else:
raise InputError(f"Lexical RHS should be string literal or integer")
def _bnf_symbol(stream: TokenStream, gram: Grammar) -> RHSItem:
"""A single identifier or literal, or a parenthesized group"""
if stream.peek().kind == TokenCat.LPAREN:
stream.take()
subseq = _bnf_rhs(stream, gram)
require(stream, TokenCat.RPAREN, consume=True)
# log.debug(f"Subsequence group: {subseq}")
return subseq
token = stream.take()
if token.kind == TokenCat.STRING or token.kind == TokenCat.CHAR:
# log.debug("Forming literal")
return gram.literal(token.value[1:-1]) # Clips quotes
elif token.kind == TokenCat.IDENT:
# log.debug("Forming symbol")
return gram.symbol(token.value)
else:
raise InputError(f"Unexpected input token {token.value}")