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* Llama — Compact syntax for short lambda
This package implements a macro named ~##~, which provides a compact way
to write short ~lambda~ expressions.
The signature of the macro is ~(## FN &rest BODY)~ and it expands to a
~lambda~ expression, which calls the function ~FN~ with the arguments ~BODY~
and returns the value of that. The arguments of the ~lambda~ expression
are derived from symbols found in ~BODY~.
Each symbol from ~%1~ through ~%9~, which appears in an unquoted part
of ~BODY~, specifies a mandatory argument. Each symbol from ~&1~ through
~&9~, which appears in an unquoted part of ~BODY~, specifies an optional
argument. The symbol ~&*~ specifies extra (~&rest~) arguments.
The shorter symbol ~%~ can be used instead of ~%1~, but using both in
the same expression is not allowed. Likewise ~&~ can be used instead
of ~&1~. These shorthands are not recognized in function position.
To support binding forms that use a vector as ~VARLIST~ (such as ~-let~
from the ~dash~ package), argument symbols are also detected inside of
vectors.
The space between ~##~ and ~FN~ can be omitted because ~##~ is read-syntax
for the symbol whose name is the empty string. If you prefer you can
place a space there anyway, and if you prefer to not use this somewhat
magical symbol at all, you can instead use the alternative name ~llama~.
Instead of:
#+begin_src emacs-lisp
(lambda (a &optional _ c &rest d)
(foo a (bar c) d))
#+end_src
you can use this macro and write:
#+begin_src emacs-lisp
(##foo %1 (bar &3) &*)
#+end_src
which expands to:
#+begin_src emacs-lisp
(lambda (%1 &optional _&2 &3 &rest &*)
(foo %1 (bar &3) &*))
#+end_src
Unused trailing arguments and mandatory unused arguments at the border
between mandatory and optional arguments are also supported:
#+begin_src emacs-lisp
(##list %1 _%3 &5 _&6)
#+end_src
becomes:
#+begin_src emacs-lisp
(lambda (%1 _%2 _%3 &optional _&4 &5 _&6)
(list %1 &5))
#+end_src
Note how ~_%3~ and ~_&6~ are removed from the body, because their names
begin with an underscore. Also note that ~_&4~ is optional, unlike the
explicitly specified ~_%3~.
Consider enabling ~llama-fontify-mode~ to highlight ~##~ and its special
arguments.
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