install.packages('Ramble')identifier creates an identifieralt combinator is similar to alternation in BNF. the parser
(alt(p1, p2)) recognises anything that p1 or p2 would.
The approach taken in this parser follows (Fairbairn86), in which either is
interpretted in a sequential (or exclusive) manner, returning the result of
the first parser to succeed, and failure if neither does.%using% is the infix operator for using%thentree% is the infix operator for the then combinator, and it is
the preferred way to use the thentree operator.ident is a parser which matches zero or more alphanumeric
characters.%alt% is the infix notation for the alt function.%then% is the infix operator for the then combinator.satisfy is a function which allows us to make parsers that recognise single symbols.natural creates a token parser for natural numberssome matches 1 or more of pattern p. in BNF notation, repetition occurs often enough to merit its own abbreviation. When zero or
more repetitions of a phrase p are admissible, we simply write
p+. The some combinator corresponds directly to this operator,
and is defined in much the same way.maybe matches 0 or 1 of pattern p. In EBNF notation, this
corresponds to a question mark ('?').many matches 0 or more of pattern p. In BNF notation,
repetition occurs often enough to merit its own abbreviation. When zero or
more repetitions of a phrase p are admissible, we simply write
p*. The many combinator corresponds directly to this operator,
and is defined in much the same way.nat is a parser which matches one or more numeric characters.item is a parser that consumes the first character of the string and
returns the rest. If it cannot consume a single character from the string, it
will emit the empty list, indicating the parser has failed.literal is a parser for single symbols. It will attempt to match the
single symbol with the first character in the string.succeed is based on the empty string symbol in the BNF notation The
succeed parser always succeeds, without actually consuming any input
string. Since the outcome of succeed does not depend on its input, its result
value must be pre-detemined, so it is included as an extra parameter.String is a combinator which allows us to build parsers which
recognise strings of symbols, rather than just single symbolssymbol creates a token for a symbolspace matches zero or more space characters.then combinator corresponds to sequencing in BNF. The parser
(then(p1, p2)) recognises anything that p1 and p2 would
if placed in succession.thentree keeps the full tree representation of the results of parsing.
Otherwise, it is identical to then.token is a new primitive that ignores any space before and after
applying a parser to a token.using combinator allows us to manipulate results from a parser, for
example building a parse tree. The parser (p %using% f) has the same
behaviour as the parser p, except that the function f is
applied to each of its result values.