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* Argot: A System For Grammar-Driven Macros
The ~argot~ system provides a macro-defining-macro called
~deflanguage~. The ~deflanguage~ macro accepts a context-free grammar,
augmented with parse handlers, and defines a macro whose body is
parsed and expanded according to that augmented grammar.
** A brief tour
In ~/examples/calc.lisp~ you see the following ~deflanguage~:
#+begin_src lisp
(deflanguage calc (:documentation "A calculator language")
(<start>
:match (:or
(:seq <subexpr> (:eof))
(:seq <value> (:eof))
(:seq <unop> (:eof))
(:seq <binop> (:eof)))
:then car)
(<expr>
:match (:or <subexpr> <value> <unop> <binop>))
(<subexpr>
:match (:{} calc))
(<value>
:match (:item)
:if numberp)
(<binop>
:match (:seq
(:@ lhs <expr>)
(:@ rhs (:+ (:seq (:or= + - / * ^ %) <expr>))))
:then (expand-binop lhs rhs))
(<unop>
:match (:seq (:or= sin cos tan -) <expr>)))
#+end_src
This defines a cacluator language that you can use like so:
#+begin_src lisp
> (calc 1)
1
> (calc 1 + 2 + 3)
6
> (calc 1 + 2 * 3)
7
> (calc (1 + 2) * 3)
9
> (calc (1 + 2) * 3 + 1)
10
> (calc (1 + 2) * (3 + 1))
12
> (calc 2 ^ (2 * (1 + 1)))
16
#+end_src
The symbol ~calc~ also has a function docstring. If you are in slime,
you can evoke ~M-x slime-documentation~ with your cursor over the
~calc~ symbol and see this:
#+begin_src
Documentation for the symbol CALC:
Function:
Arglist: (&BODY TOKENS)
A calculator language
<START> ::= (<SUBEXPR> ::EOF:: | <VALUE> ::EOF:: | <UNOP> ::EOF:: | <BINOP> ::EOF::)
<EXPR> ::= (<SUBEXPR> | <VALUE> | <UNOP> | <BINOP>)
<SUBEXPR> ::= {CALC}
<VALUE> ::= ::TOKEN::
<BINOP> ::= <EXPR> ('+' | '-' | '/' | '*' | '^' | '%') <EXPR>+
<UNOP> ::= ('SIN' | 'COS' | 'TAN' | '-') <EXPR>
KEY:
::TOKEN:: Any ole token
::EOF:: Explicitly match the end of the input
{GRAMMAR} Parse a sublist of tokens with GRAMMAR
(a|b|..) One of the alternavites a b ...
PATTERN+ One or more PATTERN
PATTERN* Zero or more PATTERN
<RULE> A nonterminal symbol - naming a parse rule
[OPT] Zero or one of OPT
#+end_src
** User Guide
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