// http://javascript.crockford.com/tdop/index.html
// Douglas Crockford 2010-06-26
+// See also http://effbot.org/zone/simple-top-down-parsing.htm
+
+
/*jslint onevar: false
*/
a = t.type;
if (a === "name") {
o = symbol_table[v];
- if (o && typeof o !== 'function') {
- a = "keyword";
- } else {
+ if (!o || typeof o === 'function') {
o = symbol_table["(name)"];
+ } else {
+ a = o.arity || "keyword";
}
} else if (a === "number") {
- o = symbol_table["(literal)"];
- a = "literal";
+ o = symbol_table["(number)"];
+ a = "literal";
} else if (a === "operator") {
o = symbol_table[v];
if (!o) {
}
};
+ /*
+ try {
+ if (console && console.debug) {
+ function print() {
+ console.debug.apply(this, arguments);
+ }
+ }
+ } catch (e) {}
+ */
+
var symbol = function (id) {
var s = symbol_table[id];
if (!s) {
return s;
};
-
-// try {
-// if (console && console.debug) {
-// function print() {
-// console.debug.apply(this, arguments);
-// }
-// }
-// } catch (e) {}
-
-
- var itself = function () {
- return this;
- };
-
- var var_table = {};
- var name_table = {};
+ var var_table;
+ var name_table;
var name_handler = function () {
var n = name_table[this.value];
symbol("(end)");
symbol("(name)").handler = name_handler;
- symbol("(literal)").handler = itself;
symbol("let").handler = lambda_handler;
symbol("=").handler = branch_handler;
symbol("in");
symbol("lambda").handler = lambda_handler;
symbol(".");
+ function make_constants() {
+
+ function make_lam2(a, b, aa) {
+ return make_lam(a, make_lam(b, aa));
+ }
+ function make_lam3(a, b, c, aa) {
+ return make_lam(a, make_lam(b, make_lam(c, aa)));
+ }
+ function make_app3(aa, bb, cc) {
+ return make_app(make_app(aa, bb), cc);
+ }
+ var u = make_var("u");
+ var v = make_var("v");
+ var x = make_var("x");
+ var s = make_var("s");
+ var z = make_var("z");
+ var uu = new Lambda_var(u);
+ var vv = new Lambda_var(v);
+ var xx = new Lambda_var(x);
+ var ss = new Lambda_var(s);
+ var zz = new Lambda_var(z);
+ var_table = { u: u, v: v, x: x, s: s, z: z};
+ name_table = {u: uu, v: vv, x: xx, s: ss, z: zz};
+ number_table = {};
+
+ // constants have their own id and arity = literal
+ // numbers have id = "(number)" and arity = literal
+ symbol("(number)").handler = function () {
+ var n = this.value;
+ var res = number_table[n];
+ if (!res) {
+ res = zz;
+ while (n > 0) {
+ n -= 1;
+ res = make_app(ss, res);
+ }
+ res = make_lam2(s, z, res);
+ number_table[this.value] = res;
+ }
+ if (this.first) {
+ return make_app(this.first.handler(), res);
+ } else {
+ return res;
+ }
+ }
+
+ var constant = function (s, v) {
+ var x = symbol(s);
+ x.handler = function () {
+ this.value = symbol_table[this.id].value;
+ if (this.first) {
+ return make_app(this.first.handler(), this.value);
+ } else {
+ return this.value;
+ }
+ };
+ x.arity = "literal";
+ x.value = v;
+ return x;
+ };
+
+ constant("S", make_lam3(u, v, x, make_app3(uu, xx, make_app(vv, xx))));
+ constant("K", make_lam2(u, v, uu));
+ constant("I", make_lam(x, xx));
+ constant("B", make_lam3(u, v, x, make_app(uu, make_app(vv, xx))));
+ constant("C", make_lam3(u, v, x, make_app3(uu, xx, vv)));
+
+ // trush \uv.vu = CI
+ constant("T", make_lam2(u, v, make_app(vv, uu)));
+ // mockingbird \u.uu = SII
+ constant("M", make_lam(u, make_app(uu, uu)));
+ // warbler \uv.uvv = C(BM(BBT) = C(BS(C(BBI)I))I
+ constant("W", make_lam2(u, v, make_app3(uu, vv, vv)));
+ // lark \uv.u(vv) = CBM = BWB
+ constant("L", make_lam2(u, v, make_app(uu, make_app(vv, vv))));
+ // Y is SLL
+
+ }
+ make_constants();
+
var expression = function (in_let) {
var t, n;
if (token.id === "\\" || token.id === "lambda") {
return t;
} else {
t.first = [];
- while (token.arity === "name") {
- t.first.push(n);
- n = token;
+ while (token.arity === "name" || token.id === "\\") {
+ if (token.id !== "\\") {
+ t.first.push(n);
+ n = token;
+ }
advance();
}
- if (token.id === ".") {
+ if (token.arity === "literal" && t.first.length === 0) {
+ t.first.push(n);
+ t.second = token;
+ advance();
+ } else if (token.id === ".") {
t.first.push(n);
advance();
t.second = expression(in_let);
n = token;
advance(")");
} else {
- if (token.arity !== "name") {
- token.error("Expected a variable name.");
+ if (token.arity !== "name" && token.arity !== "literal") {
+ token.error("Expected a variable name or literal.");
}
token.first = n;
n = token;