Parser -- the class of all parsers

Description

A parser is a type of function that parses a sequence of tokens. Tokens can be anything except null. A parser p is called repeatedly, like this: p t, one token at a time. The return value that indicates acceptance of the input token is a new parser, which replaces the old, and is ready to accept the next token; the original parser p should not change its internal state. The return value that indicates rejection of the input token is null. Rejection may be interpreted as a syntax error.

When the input stream is exhausted, we call p one more time like this: p null. The return value is null if the parser is not in a terminal state. Otherwise the return value is the parsed (and possibly evaluated) result.

Methods that use a parser :

* Parser -- repetition of a parser
+ Parser -- repetition of a parser at least once
Parser @ Parser -- see andP -- parser conjunction
Parser @ String -- see andP -- parser conjunction
String @ Parser -- see andP -- parser conjunction
Function % Parser -- transform the value returned by a parser
Parser | Parser -- see orP -- parsing alternatives
Parser | String -- see orP -- parsing alternatives
String | Parser -- see orP -- parsing alternatives
Parser : Analyzer -- combine a parser with a lexical analyzer to make a complete system

Fixed objects of class Parser :

deadParser -- a parser which accepts no tokens and is not in a terminal state
letterParser -- a parser that accepts a single letter and returns it
NNParser -- a parser that accepts (and returns) a natural number, one character at a time
nullParser -- a terminal parser that returns the value nil
optionalSignParser -- a parser that accepts an optional plus sign or minus sign
QQParser -- a parser that accepts (and returns) a rational number, one character at a time
ZZParser -- a parser that accepts (and returns) an integer, one character at a time

For the programmer

The object Parser is a self initializing type, with ancestor classes FunctionClosure < Function < Thing.

deadParser -- a parser which accepts no tokens and is not in a terminal state
terminalParser -- produce a parser in a terminal state
nullParser -- a terminal parser that returns the value nil
futureParser -- forward reference to a parser not defined yet
letterParser -- a parser that accepts a single letter and returns it
constParser -- produce a parser that accepts a fixed string, one character at a time
optionalSignParser -- a parser that accepts an optional plus sign or minus sign
NNParser -- a parser that accepts (and returns) a natural number, one character at a time
ZZParser -- a parser that accepts (and returns) an integer, one character at a time
QQParser -- a parser that accepts (and returns) a rational number, one character at a time

making new parsers from old ones

optP -- making a parser optional
orP -- parsing alternatives
andP -- parser conjunction
* Parser -- repetition of a parser
+ Parser -- repetition of a parser at least once
Function % Parser -- transform the value returned by a parser