chriswarbo-net: 2d205a4611aa4a22d96c6b7cd3b29038c4251bdf

     1: // Combinatory logic with the S and K combinators
     2: // Combinators are either 'S', 'K' or an array of combinators
     3: 
     4: window.step_combinator = function(comb, allowed) {
     5: 	// "allowed" is a nullary function which returns a boolean, and
     6: 	// is called before each rewrite step. If it returns false, the
     7: 	// rewrite is aborted at its current state and this is returned.
     8: 	if (typeof allowed != typeof function(a){return a;}) {
     9: 		// If we've been given no condition, allow all rewrites
    10: 		allowed = function() { return true; };
    11: 	}
    12: 	// These are the base cases of our recursion
    13: 	if (comb === 'S') { return comb; }
    14: 	if (comb === 'K') { return comb; }
    15: 	
    16: 	// These are our rewrite rules
    17: 	// K x y -> x
    18: 	var pos = jQuery.inArray('K', comb);
    19: 	var args;
    20: 	if (pos >= 0 && pos < comb.length - 3 && allowed()) {
    21: 		args = comb.splice(pos, 3); // Pop off the elements
    22: 		comb.splice(pos, 0, args[1]); // Put the first argument to K back
    23: 	}
    24: 	// S x y z -> (x z) (y z)
    25: 	pos = jQuery.inArray('S', comb);
    26: 	if (pos >= 0 && pos < comb.length - 4 && allowed()) {
    27: 		args = comb.splice(pos, 4); // Pop off the elements
    28: 		comb.splice(pos, 0, [args[1], args[3]], [args[2], args[3]]); // Put the modified tree back
    29: 	}
    30: 	return _.map(comb, function(c) {return window.step_combinator(c, allowed); });
    31: };