Testing a cool posting style excerpted from Matt Might

In his excellent blog on the Y-combinator, Matt Might - a professor at my alma mater, the University of Utah - uses a technique for placing executable Javascript code in the flow of his document.
Right now I am pasting his code into the html editor of my Google blogger to see if I can reproduce the trick he uses. The part that follows is in double quotes, as it is Matt's work:


Open Double Quote


The following example expresses the factorial function without using recursion:

// A "functional" is just a function that takes // another function as input. // The Y combinator finds the fixed point // of the "functional" passed in as an argument. // Thus, the Y combinator satisfies the property: // Y(F) = F(Y(F)) // Note that Y does not reference itself: var Y = function (F) { return (function (x) { return F(function (y) { return (x(x))(y); }); })(function (x) { return F(function (y) { return (x(x))(y); }); }); }; // (In fact, all functions above are anonymous!) // FactGen is the functional whose fixed point is // factorial. // That is, if you pass the factorial function to // FactGen, you get back the factorial function. // Since the Y combinator returns the fixed point // of a functional, applying the Y combinator to // FactGen returns the factorial function! // Note that FactGen does not reference itself: var FactGen = function (fact) { return (function (n) { return ((n == 0) ? 1 : (n * fact(n - 1))); }); }; // (In fact, all functions above are anonymous!) // FactGen is the functional whose fixed point is // factorial. // That is, if you pass the factorial function to // FactGen, you get back the factorial function. // Since the Y combinator returns the fixed point // of a functional, applying the Y combinator to // FactGen returns the factorial function! // Note that FactGen does not reference itself: var FactGen = function (fact) { return (function(n) { return ((n == 0) ? 1 : (n*fact(n-1))) ; }); } ; document.getElementById("result1").innerHTML = (Y(FactGen))(6) ;

[result1]

Take a close look at the definition of Y. It uses only three kinds of expression: anonymous functions, variable reference and function application.

Close Double Quote


Back to my words: Note that even though this is a blog, the html is still functional and the Javascript program executes when the "Evaluate" button is pressed. So handy for making those subtle programming points!


If you right click this page and choose, "View Source", You can see the embedding of the code between lines 456 and 524. A short preamble and "postamble" are all that are required. Thanks Matt!


Footnotes:
Attempts to paste commented html tags were futile as they were evaluated. Attempts to color the code red didn't work either.