Add script_templates and ensure output values can be extracted by

scripting framework

Capturing the output of Scala script for the scripting framework turned
out to be tricky. Values (or variables) computed by Scala script engine
are not added to bindings of CompiledScript AFAICT. Only way to extract
them is to eval the variable and capture the return.

Author: keithschulze

src/main/java/org/scijava/plugins/scripting/scala/ScalaScriptEngine.java

@@ -0,0 +1,71 @@
+/*
+ * #%L
+ * JSR-223-compliant Scala scripting language plugin.
+ * %%
+ * Copyright (C) 2013 - 2016 Board of Regents of the University of
+ * Wisconsin-Madison.
+ * %%
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ * #L%
+ */
+
+package org.scijava.plugins.scripting.scala;
+
+import javax.script.ScriptEngine;
+import javax.script.ScriptException;
+
+import org.scijava.script.AdaptedScriptEngine;
+
+/**
+ * Scala interpreter
+ *
+ * @author Keith Schulze
+ * @see ScriptEngine
+ */
+public class ScalaScriptEngine extends AdaptedScriptEngine {
+
+    public ScalaScriptEngine(ScriptEngine engine) {
+        super(engine);
+    }
+
+    @Override
+    public Object get(String key) {
+        // First try to get value from bindings
+        Object value = super.get(key);
+
+        // NB: Extracting values from Scala Script Engine are a little tricky.
+        // Values (variables) initialised or computed in the script are
+        // not added to the bindings of the CompiledScript AFAICT. Therefore
+        // the only way to extract them is to evaluate the variable and
+        // capture the return. If it evaluates to null or throws a
+        // a ScriptException, we simply return null.
+        if (value == null) try {
+            value = super.eval(key);
+        } catch (ScriptException ignored) {
+            // HACK: Explicitly ignore ScriptException, which arises if
+            // key is not found. This feels bad because it fails silently
+            // for the user, but it mimics behaviour in other script langs.
+        }
+
+        return value;
+    }
+}

src/main/java/org/scijava/plugins/scripting/scala/ScalaScriptLanguage.java

@@ -70,8 +70,10 @@ public ScriptEngine getScriptEngine() {
 		final Settings settings = new Settings();
 		settings.classpath().value_$eq(getClasspath());
 
-		return Scripted.apply(new Scripted.Factory(), settings,
-			new NewLinePrintWriter(new ConsoleWriter(), true));
+		Scripted eng = Scripted.apply(new Scripted.Factory(), settings,
+				new NewLinePrintWriter(new ConsoleWriter(), true));
+
+		return new ScalaScriptEngine(eng);
 	}
 
 	/** Retrieves the current classpath as a string. */

src/main/resources/script_templates/Examples/Blur_Image.scala

@@ -0,0 +1,26 @@
+// @Dataset inputImg
+// @OpService ops
+// @OUTPUT Dataset(label="Blurred") blurredImg
+
+// A simple Scala script that blurs an input image with
+// a Gaussian filter. Note that you must have an image
+// open to run this script.
+// It is the duty of the scripting framework to bind
+// the input image and then display the blurred output
+// image. It also binds the ImageJ OpService for filtering.
+
+import net.imagej.ops.OpService
+import net.imglib2.img.Img
+import net.imglib2.`type`.numeric.RealType
+
+// Scala is a compiled language with a very strict/powerful
+// type system. We need to cast any parameters that are bound
+// at runtime to their known type otherwise the Scala compiler
+// will throw Type errors.
+
+// Dataset extends Img[RealType[_]]. We cast directly to
+// Img[RealType[_]] to narrow the underlying pixel type,
+// which is required for the Gauss filter.
+val img = inputImg.asInstanceOf[Img[T] forSome {type T <: RealType[T]}]
+
+val blurredImg = ops.asInstanceOf[OpService].filter().gauss(img, 2)

src/main/resources/script_templates/Intro/Greeting.scala

@@ -0,0 +1,9 @@
+// @String(label="Please enter your name",description="Name field") name
+// @OUTPUT String greeting
+
+// A Scala script with parameters
+// It is the duty of the scripting framework to harvest
+// the 'name' parameter from the user, and then display
+// the 'greeting' output parameter, based on it's type.
+
+val greeting = s"Hello, ${name}!"

src/main/resources/script_templates/Intro/Hello_World.scala

@@ -0,0 +1,5 @@
+// A very simple Scala script.
+// It is the duty of the scripting framework to display
+// the script's return value, based on its type.
+
+"Hello, World!"