Improve debugging flow

examples/fallback/main.hank

@@ -0,0 +1,18 @@
+-> start
+
+== start
+* Sometimes
+* you try everything
+* and everything
+* and nothing seems to get you anywhere.
+* -> end
+- -> start
+
+== end
+This is what fallback choices are for!
+* One other thing -> end
+* ->
+    You can put content in a fallback choice using the "choice then arrow" syntax.
+
+
+/* TODO test the situation where we want to allow multiple fallbacks, each one having a different condition */    

examples/fallback/test1.hlog

@@ -0,0 +1,24 @@
+* Sometimes
+* you try everything
+* and everything
+* and nothing seems to get you anywhere.
+>>> 3
+and nothing seems to get you anywhere.
+* Sometimes
+* you try everything
+* and everything
+>>> 0
+Sometimes
+* you try everything
+* and everything
+>>> 1
+and everything
+* you try everything
+>>> 0
+you try everything
+This is what fallback choices are for!
+* One other thing
+>>> 0
+One other thing
+This is what fallback choices are for!
+You can put content in a fallback choice using the "choice then arrow" syntax.

src/RunStoryDemo.hx

@@ -5,10 +5,10 @@ class RunStoryDemo {
         var input = Sys.stdin();
 
         var debug = false;
-        trace("Enter a path to a hank story file. Prepend with * for debug prints. (default is examples/main.hank): ");
+        trace("Enter a path to a hank story file. Prepend with * for debug prints. (default is examples/main/main.hank): ");
         var path = input.readLine();
         path = if (path.length == 0) {
-            "examples/main.hank";
+            "examples/main/main.hank";
         } else {
             if (path.charAt(0) == '*') {
                 debug = true;
@@ -18,7 +18,7 @@ class RunStoryDemo {
             }
         }
 
-        var story: Story = new Story(false, StringTools.replace(path, '.hank', '.hog'));
+        var story: Story = new Story(false, StringTools.replace(path, '.hank', '.hlog'));
         story.loadScript(path);
         var frame = StoryFrame.Finished;
         do {

src/Story.hx

@@ -721,7 +721,17 @@ class Story {
                 }
                 
                 var availableChoices = [for (choice in collectChoicesToDisplay()) choice.text];
-                return if (availableChoices.length > 0) HasChoices(availableChoices) else Error("Ran out of available choices.");
+                if (availableChoices.length > 0) {
+                    return HasChoices(availableChoices);
+                } 
+                else {
+                    var fallback = collectFallbackChoice();
+                    if (fallback != null) {
+                        return chooseFallbackChoice(fallback);
+                    } else {
+                        throw 'Ran out of available choices at ${currentLineMapKey()}.';
+                    }
+                }
 
             // Execute gathers by updating the choice depth and continuing from that point
             case Gather(label, depth, nextPartType):
@@ -867,20 +877,8 @@ class Story {
             case Some(target):
                 divert(target);
             case None:
-                // Otherwise, find the line where the choice taken occurs
-                for (i in currentLineIdx...scriptLines.length) {
-                    switch (scriptLines[i].type) {
-                        case DeclareChoice(choice):
-                            if (choice.id == choiceTaken.id) {
-                                gotoLine(i);
-                                break;
-                            }
-                        default:
-                    }
-                }
-
-                // Move to the line following this choice.
-                stepLine();
+                // Otherwise, follow the choice's branch.
+                gotoChoiceBranch(choiceTaken);
         }
         
         // Log the choice's index to the transcript
@@ -889,6 +887,23 @@ class Story {
         return choiceTaken.text;
     }
 
+    private function gotoChoiceBranch(choiceTaken: Choice) {
+        // find the line where the choice taken occurs
+        for (i in currentLineIdx...scriptLines.length) {
+            switch (scriptLines[i].type) {
+                case DeclareChoice(choice):
+                    if (choice.id == choiceTaken.id) {
+                        gotoLine(i);
+                        break;
+                    }
+                default:
+            }
+        }
+
+        // Move to the line following this choice.
+        stepLine();
+    }
+
     /**
     Search for the next gather that applies to the current choice depth, and follow it.
     @return If a suitable gather is found, Empty. Otherwise, an Error frame.
@@ -974,6 +989,35 @@ class Story {
         return choices;
     }
 
+    private function collectFallbackChoice() {
+        var choices = collectRawChoices();
+        for (choice in choices) {
+            if (choice.text.length == 0) {
+                return choice;
+            }
+        }
+
+        return null;
+    }
+
+    /**
+    Return the first frame following a fallback choice, pushing the flow forward down that branch.
+    **/
+    private function chooseFallbackChoice(choice: Choice): StoryFrame {
+        switch (choice.divertTarget) {
+            case Some(target):
+                // "choice then arrow syntax" should simply evaluate the lines following this choice
+                if (target.length == 0) {
+                    gotoChoiceBranch(choice);
+                    return nextFrame();
+                } else {
+                    return divert(target);
+                }
+            default:
+                throw 'Syntax error in fallback choice: no ->';
+        }
+    }
+
     /**
     Check if a choice's display condition is satisfied
     **/
@@ -1044,7 +1088,11 @@ class Story {
                 // Check that the choice hasn't been chosen before if it is a one-time-only
                 if (choicesEliminated.indexOf(choice.id) == -1) {
                     // fill the choice's h expressions after removing the flag expression
-                    choices.push(choiceToDisplay(choice, chosen));
+                    var displayChoice = choiceToDisplay(choice, chosen);
+                    // Don't display fallback choices (choices with no text)
+                    if (StringTools.trim(displayChoice.text.split('->')[0]).length > 0) {
+                        choices.push(displayChoice);
+                    }
                 } else {
                     // debugTrace('can\'t display "${choice.text}" because it has expired.');
                 }

src/StoryTestCase.hx

@@ -37,7 +37,7 @@ class StoryTestCase extends utest.Test {
             try {
                 frame = story.nextFrame();
             } catch (e: Dynamic) {
-                trace('Error at ${story.lastLineID}');
+                trace('Error at ${story.lastLineID} while validating ${transcriptFile}');
 
                 throw e;
             }
@@ -69,13 +69,19 @@ class StoryTestCase extends utest.Test {
                 continue;
             } else if (StringTools.startsWith(line, ">>>")) {
                 // Make the choice given.
-                var output = story.choose(Std.parseInt(StringTools.trim(line.substr(3))));
-                if (debugPrints) {
-                    trace(output);
-                }
-                if (fullTranscript || transcriptLines.length > i+1) {
-                    // Assert that its output equals the transcript's expected choice output.
-                    Assert.equals(transcriptLines[++i], output);
+                try {
+                    var output = story.choose(Std.parseInt(StringTools.trim(line.substr(3))));
+                    if (debugPrints) {
+                        trace(output);
+                    }
+                    if (fullTranscript || transcriptLines.length > i+1) {
+                        // Assert that its output equals the transcript's expected choice output.
+                        Assert.equals(transcriptLines[++i], output);
+                    }
+                } catch (e: Dynamic) {
+                    trace('Error at ${story.lastLineID} while validating ${transcriptFile}');
+
+                    throw e;
                 }
             } else if (StringTools.startsWith(line, "#")) {
                 // Allow comments in a transcript that need not be validated in any way