Warning: this is an htmlized version!
The original is across this link,
and the conversion rules are here.
/*
 * (find-angg "vtutil/pio_fontx.c")
 * (find-libcnode "String Length")
 * (find-libcnode "Copying and Concatenation")
 * (find-man "3 strlen")
 * (find-man "3 strcpy")
 * (find-lua51manualw3m "#lua_register")
 *
 * (find-books "__comp/__comp.el" "ierusalimschy")
 * (find-pil2page (+ 19 241)  "26. Calling C from Lua")
 * (find-pil2text (+ 19 241)  "Calling C from Lua")
 * (find-pil2page (+ 19 245) "luaL_register(L, \"mylib\", mylib)")
 * (find-pil2text (+ 19 245) "luaL_register(L, \"mylib\", mylib)")
 * (defun c () (interactive) (find-sh0 "gcc -Wall -shared -I$LUA51SRC/include -o sexpskeleton.so sexpskeleton.c"))
 * (find-lua51manualw3m "#pdf-package.loadlib")
 * (find-angg "LUA/lua50init.lua" "loadbitlib")

* (eepitch-lua51)
* (eepitch-kill)
* (eepitch-lua51)
so = "/home/edrx/blogme4/sexpskeleton.so"
so = os.getenv("PWD").."/sexpskeleton.so"
init = "luaopen_sexpskeleton"
f = assert(package.loadlib(so, init))()
PP(f('a\t"foo""foo" b(c () \\d\"ef\")'))

*/

#include <string.h>
#include <stdio.h>
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"

static int l_sexpskeleton(lua_State *L) {
  const char *origstr = luaL_checkstring(L, 1);
  char s[258];			/* skeleton */
  int len, i, depth;
  /* discard long lines */
  if (strlen(origstr) > 256)
    return 0;
  /* skeleton is initially a copy of origstr */
  strcpy(s, origstr);
  len = strlen(s);
  /* convert tabs to spaces */
  for (i=0; i<len; ++i)
    if (s[i]==9)
      s[i] = 32;
  /* ignore trailing whitespace */
  for (; len>0 && s[len-1]==32; --len);   
  /* sexp hyperlinks must end with ')' */
  if (len==0 || s[len-1]!=')')
    return 0;
  /* simplify backslashes */
  for (i=0; i<len-1; ++i)
    if (s[i]=='\\') {
      s[i] = '_'; s[i+1] = '_';
    }
  /* simplify strings */
  for (i=len-1; i>=0; --i)
    if (s[i]=='\"')
      for (--i; i>=0 && s[i]!='\"'; --i)
        s[i] = '_';
  // if (1) lua_pushstring(L, s); return 1; /* !!! */
  /* find the beginning of the sexp */
  for (i=len-2, depth=1; i>=0 && depth>0; --i)
    if (s[i]==')') { depth++; } else
    if (s[i]=='(') { depth--; }
  /* unbalanced parentheses? */
  if (depth!=0)
    return 0;
  /* wipe out everything before the sexp */
  for (; i>=0; --i)
    s[i] = 32;
  /* return the skeleton */
  lua_pushstring(L, s);
  return 1;
}

int luaopen_sexpskeleton (lua_State *L) {
  lua_pushcfunction(L, l_sexpskeleton);
  return 1;
}