Merge pull request #185 from jneen/topic/linter-example

Adds linter example

examples/linter.js

@@ -0,0 +1,160 @@
+'use strict';
+
+// Run me with Node to see my output!
+
+let util = require('util');
+let P = require('..');
+
+///////////////////////////////////////////////////////////////////////
+
+// -*- Parser -*-
+
+let Lang = P.createLanguage({
+
+ s0: () => P.regexp(/[ ]*/),
+ s1: () => P.regexp(/[ ]+/),
+ Whitespace: () => P.regexp(/[ \n]*/),
+ NotNewline: () => P.regexp(/[^\n]*/),
+ Comma: () => P.string(','),
+ Comment: r => r.NotNewline.wrap(P.string('//'), P.string('\n')),
+ End: r => P.alt(P.string(';'), r._, P.string('\n'), P.eof),
+ _: r => r.Comment.sepBy(r.Whitespace).trim(r.Whitespace),
+
+ Program: r =>
+ r.Statement
+ .many()
+ .trim(r._)
+ .node('Program'),
+
+ Statement: r =>
+ P.alt(
+ r.Declaration,
+ r.Assignment,
+ r.Call
+ ),
+
+ Declaration: r =>
+ P.seqObj(
+ P.string('var'),
+ r.s1,
+ ['identifier', r.Identifier],
+ r.s0,
+ P.string('='),
+ r.s0,
+ ['initialValue', r.Expression],
+ r.End
+ ).node('Declaration'),
+
+ Assignment: r =>
+ P.seqObj(
+ ['identifier', r.Identifier],
+ r.s0,
+ P.string('='),
+ r.s0,
+ ['newValue', r.Expression],
+ r.End
+ ).node('Assignment'),
+
+ Call: r =>
+ P.seqObj(
+ ['function', r.Expression],
+ P.string('('),
+ ['arguments', r.Expression.trim(r._).sepBy(r.Comma)],
+ P.string(')')
+ ).node('Call'),
+
+ Expression: r =>
+ P.alt(r.Number, r.Reference),
+
+ Number: () => P.regexp(/[0-9]+/).map(Number).node('Number'),
+ Identifier: () => P.regexp(/[a-z]+/).node('Identifier'),
+ Reference: r => r.Identifier.node('Reference'),
+
+});
+
+// -*- Linter -*-
+
+// NOTE: This simplified language only has global scope. Most real languages
+// have layers of scope, so your scope data structure will need to be something
+// more complicated than just an object keeping track of variable names.
+
+let scope = null;
+let messages = null;
+
+function noLint() {
+ // This function intentionally left blank
+}
+
+let lintHelpers = {
+
+ Program(node) {
+ node.value.forEach(lint_);
+ },
+
+ Declaration(node) {
+ scope[node.value.identifier.value] = true;
+ lint_(node.value.initialValue);
+ },
+
+ Reference(node) {
+ let name = node.value.value;
+ if (!scope.hasOwnProperty(name)) {
+ messages.push('undeclared variable ' + name);
+ }
+ },
+
+ Assignment(node) {
+ lint_(node.value.newValue);
+ },
+
+ Call(node) {
+ lint_(node.value.function);
+ node.value.arguments.forEach(lint_);
+ },
+
+ Number: noLint,
+
+};
+
+function lint_(node) {
+ if (!node) {
+ throw new TypeError('not an AST node: ' + node);
+ }
+ if (!lintHelpers.hasOwnProperty(node.name)) {
+ throw new TypeError('no lint helper for ' + node.name);
+ }
+ return lintHelpers[node.name](node);
+}
+
+function lint(node) {
+ scope = {};
+ messages = [];
+ lint_(node);
+ return messages;
+}
+
+///////////////////////////////////////////////////////////////////////
+
+let text = `\
+// nice stuff
+var x = 1 // declare this one
+
+x = 2
+
+// Notice this variable is undeclared.
+y = 3
+
+// And f is undeclared too...
+f(x, y, 3)
+`;
+
+function prettyPrint(x) {
+ let opts = {depth: null, colors: 'auto'};
+ let s = util.inspect(x, opts);
+ console.log(s);
+}
+
+let ast = Lang.Program.tryParse(text);
+let linterMessages = lint(ast);
+prettyPrint(linterMessages);
+prettyPrint(ast);