lambda

➜  purescript git:(master) ✗ ./.cabal-sandbox/bin/psc --no-prelude -s
module Foo where
f = \o -> o {foo = 3}

(function (_ps) {
    "use strict";
    _ps.Foo = (function (module) {
        var f = function (o) {
            var newObj = {};
            for (var key in o) {
                if (o.hasOwnProperty(key)) {
                    newObj[key] = o[key];
                };
            };
            newObj[foo] = 3;
            return newObj;
        };
        module.f = f;
        return module;
    })(_ps.Foo || {});
})((typeof module !== "undefined" && module.exports) ? module.exports : (typeof window !== "undefined") ? window.PS = window.PS || {} : (function () {
    throw "PureScript doesn't know how to export modules in the current environment";
})());

non-lambda

➜  purescript git:(master) ✗ ./.cabal-sandbox/bin/psc --no-prelude -s
module Foo where
f o = o {foo = 3}

(function (_ps) {
    "use strict";
    _ps.Foo = (function (module) {
        var f = function (_1) {
            return (function () {
                var newObj = {};
                for (var key in _1) {
                    if (_1.hasOwnProperty(key)) {
                        newObj[key] = _1[key];
                    };
                };
                newObj[foo] = 3;
                return newObj;
            })();
            throw "Failed pattern match";
        };
        module.f = f;
        return module;
    })(_ps.Foo || {});
})((typeof module !== "undefined" && module.exports) ? module.exports : (typeof window !== "undefined") ? window.PS = window.PS || {} : (function () {
    throw "PureScript doesn't know how to export modules in the current environment";
})());