[wg-camlp4] My P4 uses

[Jun Furuse]

Hi,

Here are the things I do with CamlP4. Lots are just simple variants of
the already reported things, though.

pa_monad for "perform" notation
===================================

URL: https://bitbucket.org/camlspotter/pa_monad_custom

I modified the original pa_monad so that I can write I/O code easily inside
perform:

    perform
      ...;
      let () = prerr_endline "debug" in     (* Writing  let () = ... in  is
boring *)
      ...;

    peform
      ...;
      \ prerr_endline "debug";          (* It is not unit monad, but a
simple unit *)
      ...;

Here \ behaves like a prefix operator with very low power,
less than function application.
I wish -ppx could provide an easy way to handle those operators with
custom connectivity configurations, including pa_monad's <--.

Code generations from data type definitions
======================================================

I have bunch of type_conv based pa modules, such as meta_conv, and other
iterator/visitor/mapper generators. I believe they can be easily ported
from
type_conv to -ppx, if we could do for sexplib.

Record like syntax
======================================================

URL: https://bitbucket.org/camlspotter/ocaml-pure-polyrecord

I introduced record like syntax for pure polymorphic records
(they are not objects so they can be marshalled). The syntax is like:

    let r = {| x = 1; y = "hello"; |}

    let x = r..x

So this is a variant of js_of_ocaml's javascript object syntax.

Perl/Python/Shell like string literals
======================================================

URL: https://bitbucket.org/camlspotter/orakuda

ORakuda provides some scripting language like string literals like:

    $/^(.*)\.mli$/                                   (* Regexp. See \ is
not doubled. *)
    $s/template/replace/g
    let myname = "Jun" in $"My name is $myname and my age is %d" 42
 (* printf *)
    let dir = Sys.getenv "HOME" in $`ls $dir`

It is very useful to write quick one time OCaml scripts, however, it
requires
a patch to CamlP4 to modify its lexer. CamlP4 can actually replace its
lexer, but
it is not integrated into pa_*.cmo framework.

So without the patch, the above must be written:

    <:m<^(.*)\.mli$>>
    <:s<template/replace/g>>
    let myname = "Jun" in <:qq<My name is $myname and my age is %d>> 42
    let dir = Sys.getenv "HOME" in <:qx<ls $dir>>

It is a bit cumbersome to type <:< >> around, but still they are useful to
me.
Note that $ is NOT used as anti-quotation for these quotes.
So I think fixing anti-quotation symbol to some character like $
uniformly is a bad idea.

I do not expect -ppx is going to handle lexer hacks like $/.../, however,
I hope it could be simple enough to write a patch to support $/.../. :-)

Partial evaluation
======================================================

In Planck LL parser library, I wrote a small pa module to partial-evaluate
monadic binds for optimzation. This is purely a program transformation,
so there should be no problem to do the same thing in -ppx.
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