Rewrite source processor script into Java.

LambdaLab/src/support/Grind.java

+package support;
+
+import java.io.IOException;
+import java.io.PrintStream;
+import java.io.UncheckedIOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
+
+/**
+ * Process all files test/solutions/*.java into
+ * corresponding files in test/exercises/*.java.
+ */
+public class Grind {
+    static class Sink implements Consumer<String> {
+        boolean removing = false;
+        final PrintStream out;
+        Sink(PrintStream out) { this.out = out; }
+        public void accept(String line) {
+            if (line.contains("//BEGINREMOVE")) {
+                removing = true;
+            } else if (line.contains("//ENDREMOVE")) {
+                removing = false;
+            } else if (!removing) {
+                out.println(line);
+            }
+        }
+    }
+
+    String subst(String line) {
+        return line.replace("package solutions;", "package exercises;")
+                   .replace("@Test", "@Test @Ignore")
+                   .replace("//UNCOMMENT//", "");
+    }
+    
+    void processFile(Path input) {
+        Path output = Paths.get("test", "exercises")
+                           .resolve(input.getName(input.getNameCount() - 1));
+        System.out.println(input + " => " + output);
+        
+        try (Stream<String> lines = Files.lines(input);
+             PrintStream out = new PrintStream(output.toFile())) {
+            lines.map(this::subst)
+                 .forEachOrdered(new Sink(out));
+        } catch (IOException ioe) {
+            throw new UncheckedIOException(ioe);
+        }
+    }
+    
+    void run() throws IOException {
+        Path dir = Paths.get("test", "solutions");
+        try (Stream<Path> paths = Files.list(dir)) {
+            paths.filter(p -> p.toString().endsWith(".java"))
+                 .forEachOrdered(this::processFile);
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        new Grind().run();
+    }
+}