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_h2 [[meta]] | meta2 | [[meta3]] | [[meta4]] | [[meta5]]

_ul See [[http://ward.asia.wiki.org/view/sweet-little-language|http://ward.asia.wiki.org/view/sweet-little-language]].

_p {b '{meta talk}} is a very reduced version of lambdatalk (see [[JS.js|meca/JS.js]] for the full version), which can work outside of the wiki:

_ul valid S-expressions are any sequences of words or well balanced nested prefixed parenthesized forms {code (first rest)}.

_ul There are {b no lambda, def, if, let} special forms, just a small set of MATH and HTML/CSS primitives:

{prewrap ['+', '*', 'sqrt', ..., fac, 
'div', 'span', 'a', 'ul', 'ol', 'li', 'dl', 'dt', 'dd', 'table', 'tr', 'td', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'p', 'b', 'i', 'u', 'center', 'br', 'hr', 'blockquote', 'del', 'sup', 'sub', 'code', 'img', 'pre']}

_ul The dictionary can be extended on demand, using the javascript syntax, see for instance the {code fac} function.

_ul {b caution}: S_expressions use rounded parentheses to trigger evaluations. Don't use rounded parentheses for other purposes, for instance to write {code (this is a comment inside parentheses)} or CSS rules containing round parentheses, for instance {code color:rgb(255,0,0)}. That explains why curly braces instead of round braces have been chosen for lambdatalk.

_h2 1) input
{textarea
 {@ id="input" 
    onkeyup="meta_evaluate()"}

(center 
  Welcome in (b metatalk), an S-expressions evaluator
  working in a console hosted in a tiny wiki,
  (b lambda tank), and its (i amazingly simple)
  language, (b lambdatalk).
)

(div 
 (@ style="font:italic 4.0em optima; 
           text-align:center;
           color:#f00;")
  (sqrt (+ (* 3 3) (* 4 4)))
)

(h1 fac[21] = (fac 21))

(pre
a
 ab
  abc
   abcd
)

(img (@ src="data/amelie_poulain.jpg" width="100%"))

Writing (foo bar) is an error, (i because foo is not in the dictionary.)
}
{center {@ id="infos"}...}

_h2 2) output
{div {@ id="output" style="padding:10px; box-shadow:0 0 8px #000;"}...}

_h2 3) javascript code

_h3 3.1) the evaluator

{pre °°
var META = (function() {

var DICT   = {};
  var regexp = /$([^\s()]*)(?:[\s]*)([^()]*)$/g;

// iterative form:
  var __eval_forms__ = function(s) {
    while (s !== (s = s.replace(regexp, eval_form)));
    return s;
  };

// recursive form:
  var eval_forms = function(s) {
    return (s !== (s = s.replace(regexp, eval_form)) )? eval_forms(s) : s;
  };

var eval_form = function() {
    var f = arguments[1] || "", r = arguments[2] || "";
    return DICT.hasOwnProperty(f) ? 
         DICT[f].apply(null, [r]) :
         "[" + f + " " + r + "]";
  };

var balance = function(s) {
    var strt = s.match(/$/g),
        stop = s.match(/$/g);
    strt = strt ? strt.length : 0;
    stop = stop ? stop.length : 0;
    return { left: strt, right: stop };
  };

return {             // public functions
    balance:balance,   // valid expressions
    eval:eval_forms,   // eval expressions
    DICT:DICT          // to add functions on demand
  }

})();  // end META
°°}

_h3 3.2) the dictionary, populated on demand

{prewrap °°
//// 1) MATH

META.DICT["+"] = function() {
    var a = arguments[0].split(" "), r;
    if (a.length === 0)      r = 0;
    else if (a.length === 1) r = a[0];
    else if (a.length === 2) r = Number(a[0]) + Number(a[1]);
    else for (var r = 0, i = 0; i < a.length; i++) r += Number(a[i]);
    return r;
  };

META.DICT["*"] = function() {
    var a = arguments[0].split(" "), r;
    if (a.length === 0)      r = 1;
    else if (a.length === 1) r = a[0];
    else if (a.length === 2) r = a[0] * a[1];
    else for (var r = 1, i = 0; i < a.length; i++) r *= a[i];
    return r;
  };

META.DICT["sqrt"] = function() {
    return Math.sqrt( arguments[0] );
  };

META.DICT["fac"] = function() {
    var fac = function(n) { return (n<1) ? 1 : n*fac(n-1); };
    return fac( arguments[0].trim() )
  };

// ... and so on.

//// 2) HTML

var htmltags = [ 'div', 'span', 'a', 'ul', 'ol', 'li', 'dl', 'dt', 'dd', 'table', 'tr', 'td', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'p', 'b', 'i', 'u', 'center', 'br', 'hr', 'blockquote', 'del', 'sup', 'sub', 'code', 'img', 'pre'];

// catch HTML attributes:
  META.DICT['@'] = function() { return '@@' + arguments[0] + '@@' };

// translate HTML tags to META tags:
  for (var i=0; i< htmltags.length; i++) {
    META.DICT[htmltags[i]] = function(tag) {
      return function() {
        var args = arguments[0].trim(); // save spaces for pre
        var attr = args.match( /@@[\s\S]*?@@/ ); 
        if (attr == null) {
          return '<'+tag+'>'+args+'< /'+tag+'>';
        } else {
          args = args.replace( attr[0], '' ).trim();
          attr = attr[0].replace(/^@@/, '').replace(/@@$/, '');
          return '<'+tag+' '+attr+'>'+args+'< /'+tag+'>';
        }
      }
    }(htmltags[i]);      
  }
°°}

_h3 3.3) the HTML interface

{prewrap °°

var meta_evaluate = function() {
  var input = document.getElementById('input').value;
  var output = '...';
  var bal = META.balance( input ); 
  document.getElementById('infos').innerHTML = 
                                  '('+bal.left+'|'+bal.right+')';
  if (bal.left === bal.right) 
    document.getElementById('output').innerHTML = META.eval( input );
};

setTimeout( meta_evaluate, 1 );
°°}

_h3 3.4) the console

{prewrap °°
{textarea {@ id="input" onkeyup="meta_evaluate()"} ... meta code ... }
{center   {@ id="infos"}...}
{div      {@ id="output"}...}
°°}

{script

var META = (function() {

//// EVALUATOR

var DICT   = {};
  var regexp = /$([^\s()]*)(?:[\s]*)([^()]*)$/g;

// iterative form
  var __eval_forms = function(s) {
    while (s !== (s = s.replace(regexp, eval_form)));
    return s;
  };

// recursive form
  var eval_forms = function(s) {
    return ( s !== (s = s.replace(regexp, eval_form)) ) ? eval_forms(s) : s;
  };

var eval_form = function() {
    var f = arguments[1] || "", r = arguments[2] || "";
    return DICT.hasOwnProperty(f) ? 
         DICT[f].apply(null, [r]) :
         "[" + f + " " + r + "]";
  };

return {             // public functions
    balance:balance,   // valid expressions
    eval:eval_forms,   // eval expressions
    DICT:DICT          // to add functions on demand
  }

})();  // end META

//// DICTIONARY (populated on demand)

//// MATH

META.DICT["sqrt"] = function() {
    return Math.sqrt( arguments[0] );
  };

META.DICT["fac"] = function() {
    var fac = function(n) { return (n<1) ? 1 : n*fac(n-1); };
    return fac( arguments[0].trim() )
  };

// ... and so on.

//// HTML

// catch HTML attributes:
  META.DICT['@'] = function() { return '@@' + arguments[0] + '@@' };

// translate HTML tags to META tags:
  for (var i=0; i< htmltags.length; i++) {
    META.DICT[htmltags[i]] = function(tag) {
      return function() {
        var args = arguments[0].trim(); // save spaces for pre
        var attr = args.match( /@@[\s\S]*?@@/ ); 
        if (attr == null) {
          return '<'+tag+'>'+args+'</'+tag+'>';
        } else {
          args = args.replace( attr[0], '' ).trim();
          attr = attr[0].replace(/^@@/, '').replace(/@@$/, '');
          return '<'+tag+' '+attr+'>'+args+'</'+tag+'>';
        }
      }
    }(htmltags[i]);      
  }

//// HTML INTERFACE

//// INSIDE THE WIKI PAGE
/*
{textarea {@ id="input" onkeyup="meta_evaluate()"} 
  ... meta code ... 
}
{center   {@ id="infos"}...}
{div      {@ id="output"}...}
*/

setTimeout( meta_evaluate, 1 );
}

{style 
pre { background:#eee; }
textarea { background:#ccc; color:#000; width:98%; height:600px; border:0; font:normal 1.1em courier; padding:1%; }
}