// 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 = 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() {
}
}
} catch (e) {}
+ */
var symbol = function (id) {
var s = symbol_table[id];
s = Object.create(original_symbol);
s.id = s.value = id;
symbol_table[id] = s;
- print(s, s.arity);
}
return s;
};
return body;
};
-
- var itself = function () {
- return this;
- };
-
symbol("(end)");
symbol("(name)").handler = name_handler;
- symbol("(literal)").handler = itself;
symbol("let").handler = lambda_handler;
symbol("=").handler = branch_handler;
symbol("in");
function make_constants() {
- var constant = function (s, v) {
- var x = symbol(s);
- x.handler = function () {
- this.value = symbol_table[this.id].value;
- return this;
- };
- x.value = v;
- x.arity = "literal";
- return x;
- };
-
function make_lam2(a, b, aa) {
return make_lam(a, make_lam(b, aa));
}
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("C", make_lam3(u, v, x, make_app3(uu, xx, vv)));
constant("W", make_lam2(u, v, make_app3(uu, vv, vv)));
constant("T", make_lam2(u, v, make_app(vv, uu)));
+
}
make_constants();
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;