Support import syntax

experiments/run-test.js

@@ -0,0 +1,14 @@
+"use strict";
+
+const fs = require("fs");
+const path = require("path");
+const util = require("util");
+
+const generate = require("../").generate;
+const parser = require("../lib/parser");
+
+let grammar = fs.readFileSync(path.join(__dirname, "test.pegjs"), { encoding: "utf-8" });
+// let parseResult = parser.parse(grammar);
+let parseResult = generate(grammar);
+
+console.log(util.inspect(parseResult, { depth: null, colors: true }));

experiments/test.pegjs

@@ -0,0 +1,5 @@
+import Foo from "./util.pegjs"
+import { CommaDelimited as DelimitedNumber } from "./delimited-number"
+
+TopLevelRule
+	= "hello"

lib/peg.js

@@ -33,10 +33,19 @@ module.exports = {
 			})
 		};
 
-		return compiler.compile(
-			config.parser.parse(grammar),
-			config.passes,
-			options
-		);
+		let parseResult = config.parser.parse(grammar);
+
+		if (parseResult.imports.length === 0) {
+			return compiler.compile(
+				parseResult,
+				config.passes,
+				options
+			);
+		} else {
+			throw new Error("`import` syntax can only be used with `generateFromFile`");
+		}
+	},
+	generateFromFile: function (path, options = {}) {
+		throw new Error(`Unimplemented`);
 	}
 };

notes.txt

@@ -0,0 +1,52 @@
+Import syntax
+
+import Foo from packagename
+import { Foo, Bar } from ./util
+import { Foo as Bar, Baz, Qux } from ../quz
+
+
+need to mangle identifiers declared in the initializer!
+
+===========
+
+Benchmark before internals changes (best of 3):
+
+$ yarn benchmark
+yarn run v1.21.1
+$ node benchmark/run
+┌─────────────────────────────────────┬───────────┬────────────┬──────────────┐
+│                Test                 │ Inp. size │ Avg. time  │  Avg. speed  │
+├─────────────────────────────────────┴───────────┴────────────┴──────────────┤
+│                                    JSON                                     │
+├─────────────────────────────────────┬───────────┬────────────┬──────────────┤
+│ Example 1                           │   0.69 kB │    0.40 ms │ 1723.63 kB/s │
+│ Example 2                           │   0.24 kB │    0.10 ms │ 2363.28 kB/s │
+│ Example 3                           │   0.59 kB │    0.40 ms │ 1474.61 kB/s │
+│ Example 4                           │   3.39 kB │    0.90 ms │ 3763.02 kB/s │
+│ Example 5                           │   0.85 kB │    0.20 ms │ 4262.70 kB/s │
+├─────────────────────────────────────┼───────────┼────────────┼──────────────┤
+│ JSON total                          │   5.75 kB │    2.00 ms │ 2877.44 kB/s │
+├─────────────────────────────────────┴───────────┴────────────┴──────────────┤
+│                                     CSS                                     │
+├─────────────────────────────────────┬───────────┬────────────┬──────────────┤
+│ Blueprint - reset.css (source)      │   1.20 kB │    3.00 ms │  401.04 kB/s │
+│ Blueprint - typography.css (source) │   3.11 kB │    5.00 ms │  621.48 kB/s │
+│ Blueprint - forms.css (source)      │   1.79 kB │    2.00 ms │  896.00 kB/s │
+│ Blueprint - grid.css (source)       │   9.54 kB │    6.50 ms │ 1467.25 kB/s │
+│ Blueprint - print.css (source)      │   1.78 kB │    1.10 ms │ 1621.09 kB/s │
+│ Blueprint - screen.css (minified)   │  11.83 kB │    8.00 ms │ 1478.64 kB/s │
+│ Blueprint - print.css (minified)    │   1.25 kB │    0.60 ms │ 2089.84 kB/s │
+│ 960.gs - reset.css (source)         │   0.99 kB │    0.50 ms │ 1980.47 kB/s │
+│ 960.gs - text.css (source)          │   0.97 kB │    0.40 ms │ 2426.76 kB/s │
+│ 960.gs - 960.css (source)           │   8.94 kB │    3.00 ms │ 2979.49 kB/s │
+│ 960.gs - 960_24_col.css (source)    │   7.48 kB │    2.60 ms │ 2877.85 kB/s │
+│ 960.gs - reset.css (minified)       │   0.63 kB │    0.50 ms │ 1265.63 kB/s │
+│ 960.gs - text.css (minified)        │   0.41 kB │    0.40 ms │ 1020.51 kB/s │
+│ 960.gs - 960.css (minified)         │   5.21 kB │    2.60 ms │ 2004.21 kB/s │
+│ 960.gs - 960_24_col.css (minified)  │   4.94 kB │    2.40 ms │ 2057.70 kB/s │
+├─────────────────────────────────────┼───────────┼────────────┼──────────────┤
+│ CSS total                           │  60.08 kB │   38.60 ms │ 1556.43 kB/s │
+├─────────────────────────────────────┼───────────┼────────────┼──────────────┤
+│ Total                               │  65.83 kB │   40.60 ms │ 1621.50 kB/s │
+└─────────────────────────────────────┴───────────┴────────────┴──────────────┘
+Done in 0.60s.

src/parser.pegjs

@@ -55,15 +55,45 @@
 // ---- Syntactic Grammar -----
 
 Grammar
-  = __ initializer:(Initializer __)? rules:(Rule __)+ {
+  = __ imports:(ImportStatement __)* initializer:(Initializer __)? rules:(Rule __)+ {
       return {
         type: "grammar",
         initializer: extractOptional(initializer, 0),
         rules: extractList(rules, 0),
+        imports: extractList(imports, 0),
         location: location()
       };
     }
 
+ImportStatement
+  = "import" _ bindings:ImportBindings _ "from" _ path:StringLiteral EOS {
+    return {
+      type: "import",
+      path: path,
+      bindings: bindings,
+      location: location()
+    };
+  }
+
+ImportBindings
+  = TopLevelImportBinding
+  / NamedImportBindings
+
+TopLevelImportBinding
+  = binding:ImportBinding {
+    return { type: "topLevelBinding", binding: binding, location: location() };
+  }
+
+NamedImportBindings
+  = "{" __ head:(ImportBinding __) tail:("," __ ImportBinding __)* "}" {
+    return { type: "namedBindings", bindings: buildList(head[0], tail, 2), location: location() };
+  }
+
+ImportBinding
+  = name:IdentifierName alias:(_ "as" _ IdentifierName)? {
+    return { type: "binding", name: name, alias: extractOptional(alias, 3), location: location() };
+  }
+
 Initializer
   = code:CodeBlock EOS {
       return { type: "initializer", code: code, location: location() };
@@ -242,6 +272,7 @@ SingleLineComment
 Identifier
   = !ReservedWord name:IdentifierName { return name; }
 
+// TODO: Can performance here be improved by using $?
 IdentifierName "identifier"
   = head:IdentifierStart tail:IdentifierPart* { return head + tail.join(""); }
 

test/unit/parser.spec.js

@@ -65,6 +65,7 @@ describe("PEG.js grammar parser", function() {
 	function oneRuleGrammar(expression) {
 		return {
 			type: "grammar",
+			imports: [],
 			initializer: null,
 			rules: [{ type: "rule", name: "start", expression: expression }]
 		};
@@ -102,6 +103,7 @@ describe("PEG.js grammar parser", function() {
 	let trivialGrammar = literalGrammar("abcd", false);
 	let twoRuleGrammar = {
 		type: "grammar",
+		imports: [],
 		initializer: null,
 		rules: [ruleA, ruleB]
 	};
@@ -226,20 +228,20 @@ describe("PEG.js grammar parser", function() {
 	// Canonical Grammar is "a = 'abcd'; b = 'efgh'; c = 'ijkl';".
 	it("parses Grammar", function() {
 		expect("\na = 'abcd';\n").to.parseAs(
-			{ type: "grammar", initializer: null, rules: [ruleA] }
+			{ type: "grammar", imports: [], initializer: null, rules: [ruleA] }
 		);
 		expect("\na = 'abcd';\nb = 'efgh';\nc = 'ijkl';\n").to.parseAs(
-			{ type: "grammar", initializer: null, rules: [ruleA, ruleB, ruleC] }
+			{ type: "grammar", imports: [], initializer: null, rules: [ruleA, ruleB, ruleC] }
 		);
 		expect("\n{ code };\na = 'abcd';\n").to.parseAs(
-			{ type: "grammar", initializer: initializer, rules: [ruleA] }
+			{ type: "grammar", imports: [], initializer: initializer, rules: [ruleA] }
 		);
 	});
 
 	// Canonical Initializer is "{ code }".
 	it("parses Initializer", function() {
 		expect("{ code };start = 'abcd'").to.parseAs(
-			{ type: "grammar", initializer: initializer, rules: [ruleStart] }
+			{ type: "grammar", imports: [], initializer: initializer, rules: [ruleStart] }
 		);
 	});