1 // Parser for lambda with let written in Simplified JavaScript
2 // by Jim Pryor 2010-09-22
3 // Stripped down from Top Down Operator Precedence : parse.js
4 // http://javascript.crockford.com/tdop/index.html
5 // Douglas Crockford 2010-06-26
7 // See also http://effbot.org/zone/simple-top-down-parsing.htm
10 /*jslint onevar: false
13 /* members create, error, message, name, prototype, stringify, toSource,
17 /*global make_var, make_app, make_lam, Lambda_var */
19 var make_parse = function () {
20 var symbol_table = {};
25 var advance = function (id) {
27 if (id && token.id !== id) {
28 token.error("Expected '" + id + "'.");
30 if (token_nr >= tokens.length) {
31 token = symbol_table["(end)"];
40 if (!o || typeof o === 'function') {
41 o = symbol_table["(name)"];
43 a = o.arity || "keyword";
45 } else if (a === "number") {
46 o = symbol_table["(number)"];
48 } else if (a === "operator") {
51 t.error("Unknown operator.");
55 t.error("Unexpected token.");
57 token = Object.create(o);
61 token.arity = a; // will be: name, keyword, literal
65 var original_symbol = {
66 handler: function () {
67 this.error("Undefined.");
73 if (console && console.debug) {
75 console.debug.apply(this, arguments);
81 var symbol = function (id) {
82 var s = symbol_table[id];
84 s = Object.create(original_symbol);
94 var name_handler = function () {
95 var n = name_table[this.value];
97 n = make_var(this.value);
98 var_table[this.value] = n;
99 n = new Lambda_var(n);
100 name_table[this.value] = n;
103 return make_app(this.first.handler(), n);
109 var branch_handler = function () {
110 var n = this.second.handler();
112 return make_app(this.first.handler(), n);
118 var lambda_handler = function () {
119 var body = this.second.handler();
121 while (this.first.length) {
122 n = this.first.pop().value;
127 name_table[n] = new Lambda_var(v);
129 body = make_lam(v, body);
135 symbol("(name)").handler = name_handler;
136 symbol("let").handler = lambda_handler;
137 symbol("=").handler = branch_handler;
139 symbol(")").handler = branch_handler;
141 symbol("\\").handler = lambda_handler;
142 symbol("lambda").handler = lambda_handler;
145 function make_constants() {
147 function make_lam2(a, b, aa) {
148 return make_lam(a, make_lam(b, aa));
150 function make_lam3(a, b, c, aa) {
151 return make_lam(a, make_lam(b, make_lam(c, aa)));
153 function make_app3(aa, bb, cc) {
154 return make_app(make_app(aa, bb), cc);
156 var u = make_var("u");
157 var v = make_var("v");
158 var x = make_var("x");
159 var s = make_var("s");
160 var z = make_var("z");
161 var uu = new Lambda_var(u);
162 var vv = new Lambda_var(v);
163 var xx = new Lambda_var(x);
164 var ss = new Lambda_var(s);
165 var zz = new Lambda_var(z);
166 var_table = { u: u, v: v, x: x, s: s, z: z};
167 name_table = {u: uu, v: vv, x: xx, s: ss, z: zz};
170 // constants have their own id and arity = literal
171 // numbers have id = "(number)" and arity = literal
172 symbol("(number)").handler = function () {
174 var res = number_table[n];
179 res = make_app(ss, res);
181 res = make_lam2(s, z, res);
182 number_table[this.value] = res;
185 return make_app(this.first.handler(), res);
191 var constant = function (s, v) {
193 x.handler = function () {
194 this.value = symbol_table[this.id].value;
196 return make_app(this.first.handler(), this.value);
206 constant("S", make_lam3(u, v, x, make_app3(uu, xx, make_app(vv, xx))));
207 constant("K", make_lam2(u, v, uu));
208 constant("I", make_lam(x, xx));
209 constant("B", make_lam3(u, v, x, make_app(uu, make_app(vv, xx))));
210 constant("C", make_lam3(u, v, x, make_app3(uu, xx, vv)));
211 constant("W", make_lam2(u, v, make_app3(uu, vv, vv)));
212 constant("T", make_lam2(u, v, make_app(vv, uu)));
217 var expression = function (in_let) {
219 if (token.id === "\\" || token.id === "lambda") {
220 token.value = "lambda";
224 if (n.arity !== "name") {
225 n.error("Expected a variable name.");
228 if (token.id === "(") {
231 t.second = expression(false);
236 while (token.arity === "name") {
241 if (token.arity === "literal" && t.first.length === 0) {
245 } else if (token.id === ".") {
248 t.second = expression(in_let);
249 } else if (t.first.length === 1) {
253 t.error("Can't parse lambda abstract.");
259 while (token.id === "(") {
261 t = expression(false);
266 if (in_let && token.id === "let" || token.id === "(end)" || token.id === ")") {
271 if (n && (in_let && token.id === "in" || token.id === "(end)" || token.id === ")")) {
273 } else if (token.id === "(") {
275 t = expression(false);
281 if (token.arity !== "name" && token.arity !== "literal") {
282 token.error("Expected a variable name or literal.");
292 return function (source) {
293 tokens = source.tokens();
300 var t = null, eq, c, base = {};
303 while (token.id === "let") {
306 if (token.arity !== "name") {
307 token.error("Expected a variable name.");
311 eq = token; // token.id === "="
313 c = expression(true);
321 // target.second = c;
327 target.second = expression(false);