Add :time command

src/main/java/de/prob2/jupyter/ProBKernel.java

@@ -29,6 +29,7 @@ import de.prob2.jupyter.commands.LoadFileCommand;
 import de.prob2.jupyter.commands.NoSuchCommandException;
 import de.prob2.jupyter.commands.PrefCommand;
 import de.prob2.jupyter.commands.SolveCommand;
+import de.prob2.jupyter.commands.TimeCommand;
 import de.prob2.jupyter.commands.VersionCommand;
 
 import io.github.spencerpark.jupyter.kernel.BaseKernel;
@@ -71,6 +72,7 @@ public final class ProBKernel extends BaseKernel {
 		this.lineCommands.put(":constants", injector.getInstance(ConstantsCommand.class));
 		this.lineCommands.put(":initialise", injector.getInstance(InitialiseCommand.class));
 		this.lineCommands.put(":init", injector.getInstance(InitialiseCommand.class));
+		this.lineCommands.put(":time", injector.getInstance(TimeCommand.class));
 		this.lineCommands.put(":groovy", injector.getInstance(GroovyCommand.class));
 		
 		this.cellCommands = new HashMap<>();

src/main/java/de/prob2/jupyter/commands/TimeCommand.java

+package de.prob2.jupyter.commands;
+
+import com.google.inject.Inject;
+
+import de.prob2.jupyter.ProBKernel;
+
+import io.github.spencerpark.jupyter.messages.DisplayData;
+
+import org.jetbrains.annotations.NotNull;
+
+public final class TimeCommand implements LineCommand {
+	private static final long NANOSECONDS_PER_SECOND = 1000000000L;
+	
+	@Inject
+	private TimeCommand() {
+		super();
+	}
+	
+	@Override
+	public @NotNull String getSyntax() {
+		return ":time COMMAND [ARGS ...]";
+	}
+	
+	@Override
+	public @NotNull String getShortHelp() {
+		return "Execute the given command and measure how long it takes to execute.";
+	}
+	
+	@Override
+	public @NotNull DisplayData run(final @NotNull ProBKernel kernel, final @NotNull String argString) {
+		final long startTime = System.nanoTime();
+		final DisplayData result = kernel.eval(argString);
+		final long stopTime = System.nanoTime();
+		final long diff = stopTime - startTime;
+		System.out.printf("Execution time: %d.%09d seconds%n", diff / NANOSECONDS_PER_SECOND, diff % NANOSECONDS_PER_SECOND);
+		return result;
+	}
+}