Create directory for Standalone Skylark

Move the REPL Skylark there.

--
MOS_MIGRATED_REVID=135467316

1 files changed, 92 insertions, 0 deletions

diff --git a/src/main/java/com/google/devtools/skylark/Skylark.java b/src/main/java/com/google/devtools/skylark/Skylark.java
new file mode 100644
index 0000000000..51053fb2a5
--- /dev/null
+++ b/src/main/java/com/google/devtools/skylark/Skylark.java
@@ -0,0 +1,92 @@
+// Copyright 2016 The Bazel Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+package com.google.devtools.skylark;
+
+import com.google.devtools.build.lib.events.Event;
+import com.google.devtools.build.lib.events.EventHandler;
+import com.google.devtools.build.lib.syntax.Environment;
+import com.google.devtools.build.lib.syntax.Mutability;
+import com.google.devtools.build.lib.syntax.Printer;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.nio.charset.Charset;
+
+/**
+ * Skylark is a standalone skylark intepreter. The environment doesn't
+ * contain Bazel-specific functions and variables. Load statements are
+ * forbidden for the moment.
+ */
+class Skylark {
+  private static final String START_PROMPT = ">> ";
+  private static final String CONTINUATION_PROMPT = ".. ";
+
+  public static final EventHandler PRINT_HANDLER = new EventHandler() {
+      @Override
+      public void handle(Event event) {
+        System.out.println(event.getMessage());
+      }
+    };
+
+  private final BufferedReader reader = new BufferedReader(
+      new InputStreamReader(System.in, Charset.defaultCharset()));
+  private final Mutability mutability = Mutability.create("interpreter");
+  private final Environment env = Environment.builder(mutability)
+      .setSkylark().setGlobals(Environment.SKYLARK).setEventHandler(PRINT_HANDLER).build();
+
+  public String prompt() {
+    StringBuilder input = new StringBuilder();
+    System.out.print(START_PROMPT);
+    try {
+      while (true) {
+        String line = reader.readLine();
+        if (line == null) {
+          return null;
+        }
+        if (line.isEmpty()) {
+          return input.toString();
+        }
+        input.append("\n").append(line);
+        System.out.print(CONTINUATION_PROMPT);
+      }
+    } catch (IOException io) {
+      io.printStackTrace();
+      return null;
+    }
+  }
+
+  public void readEvalPrintLoop() {
+    String input;
+    while ((input = prompt()) != null) {
+      try {
+        Object result = env.eval(input);
+        if (result != null) {
+          System.out.println(Printer.repr(result));
+        }
+      } catch (Exception e) {
+        e.printStackTrace();
+      }
+    }
+  }
+
+  public static void main(String[] args) {
+    if (args.length == 0) {
+       new Skylark().readEvalPrintLoop();
+    } else {
+      System.err.println("no argument expected");
+      System.exit(1);
+    }
+  }
+}