can't redefine church built-ins and if you try to, errors are very opaque.

[feste]

CODE EXAMPLE:

(define (plus a b) (+ a b))
(plus 1 1)

ERROR:

Cannot call method 'split' of undefined

/home/feste/webchurch/church:58
    throw e
          ^
TypeError: Cannot call method 'split' of undefined
    at evaluate (/home/feste/webchurch/evaluate.js:211:25)
    at Object.<anonymous> (/home/feste/webchurch/church:54:25)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:901:3

[longouyang]

For reference, the generated javascript looks like this:

(function () {
        var formatResult = require('./util.js').format_result;
    var churchToBareJs = require('./evaluate').churchToBareJs;
    var __pr = require('./probabilistic-js');
    __pr.openModule(__pr);
    var __ch = require('./church_builtins');
    openModule(__ch);
    var plus = function (x, y) {
        enterfn(0);
        var call0 = plus(x, y);
        leavefn();
        return call0;
    };
    enterfn(1);
    var call1 = plus(1, 2);
    leavefn();
    return call1;
}());

There is an obvious problem of recursive function definition here. Ideally, we might do something like:

var old_plus = plus;
var plus = function(x, y) {
enterfn(0);
var call0 = old_plus(x,y);

i.e., detect whenever user code will overshadow old builtins (but in a way that still uses the old builtins) and change generated js accordingly. I could see this being hard, though.

Also, while in looking into this, I've found some other strange edge cases, which I'll post soon.

[longouyang]

Some other strange edge cases:

;; works
(define f +)
(eval '(f 1 2))

;; fails
(define plus +)
(eval '(plus 1 2))

;; fails (weird)
(define plus +)
(eval '(+ 1 2))

;; fails (recursive define)
(define (plus x y) (+ x y))
(plus 1 2)