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packages/petitparser/example/lispshell/lispshell.dart

Index: packages/petitparser/example/lispshell/lispshell.dart
diff --git a/packages/petitparser/example/lispshell/lispshell.dart b/packages/petitparser/example/lispshell/lispshell.dart
new file mode 100644
index 0000000000000000000000000000000000000000..9ef6e51c5386e661da1934e06451193a72aa03ed
--- /dev/null
+++ b/packages/petitparser/example/lispshell/lispshell.dart
@@ -0,0 +1,88 @@
+library petitparser.example.lispshell;
+
+import 'dart:io';
+import 'dart:async';
+import 'dart:convert';
+
+import 'package:petitparser/petitparser.dart';
+import 'package:petitparser/lisp.dart';
+
+/// Read, evaluate, print loop.
+void evalInteractive(Parser parser, Environment env, Stream<String> input,
+    IOSink output, IOSink error) {
+  output.write('>> ');
+  input.listen((String line) {
+    try {
+      output.writeln('=> ${evalString(parser, env, line)}');
+    } on ParserError catch (exception) {
+      error.writeln('Parser error: ' + exception.toString());
+    } on Error catch (exception) {
+      error.writeln(exception.toString());
+    }
+    output.write('>> ');
+  });
+}
+
+/// Entry point for the command line interpreter.
+void main(List<String> arguments) {
+
+  // default options
+  var standardLibrary = true;
+  var interactiveMode = false;
+  var files = new List();
+
+  // parse arguments
+  for (var option in arguments) {
+    if (option.startsWith('-') && files.isEmpty) {
+      if (option == '-n') {
+        standardLibrary = false;
+      } else if (option == '-i') {
+        interactiveMode = true;
+      } else if (option == '-?') {
+        print('${Platform.executable} lisp.dart -n -i [files]');
+        print(' -i enforces the interactive mode');
+        print(' -n does not load the standard library');
+        exit(0);
+      } else {
+        print('Unknown option: $option');
+        exit(1);
+      }
+    } else {
+      var file = new File(option);
+      if (file.existsSync()) {
+        files.add(file);
+      } else {
+        print('File not found: $option');
+        exit(2);
+      }
+    }
+  }
+
+  // evaluation context
+  var environment = Natives.import(new Environment());
+
+  // add additional primitives
+  environment.define(new Name('exit'), (env, args) => exit(args == null ? 0 : args.head));
+  environment.define(new Name('sleep'), (env, args) => sleep(new Duration(milliseconds: args.head)));
+
+  // process standard library
+  if (standardLibrary) {
+    environment = Standard.import(environment.create());
+  }
+
+  // create empty context
+  environment = environment.create();
+
+  // process files given as argument
+  files.forEach((file) {
+    evalString(lispParser, environment, file.readAsStringSync());
+  });
+
+  // process console input
+  if (interactiveMode || files.isEmpty) {
+    var input = stdin
+        .transform(SYSTEM_ENCODING.decoder)
+        .transform(new LineSplitter());
+    evalInteractive(lispParser, environment, input, stdout, stderr);
+  }
+}