Reintroduce options block to scene file grammar; remove scene block

src/fart.propane

@@ -31,7 +31,6 @@ token lcurly /\{/;
 token lt /</;
 token options;
 token rcurly /\}/;
-token scene;
 token width;
 
 token uint /\d+/ <<
@@ -47,7 +46,7 @@ token number /-?\d+(\.\d+)?/ <<
     }
 >>
 
-Start -> RenderParams Scene;
+Start -> Options? SceneItems;
 
 Background -> background Vector;
 
@@ -56,14 +55,14 @@ Height -> height uint;
 Number -> uint;
 Number -> number;
 
-RenderParams -> ;
+Options -> options lcurly OptionsItems rcurly;
-RenderParams -> RenderParam RenderParams;
 
-RenderParam -> Background;
+OptionsItems -> ;
-RenderParam -> Height;
+OptionsItems -> OptionsItem OptionsItems;
-RenderParam -> Width;
 
-Scene -> scene lcurly SceneItems rcurly;
+OptionsItem -> Background;
+OptionsItem -> Height;
+OptionsItem -> Width;
 
 SceneItems -> ;
 

src/fart/Parser.cpp

@@ -116,19 +116,21 @@ Scene * Parser::build_scene(const string_view & input_file, PStart start)
 {
     Scene * scene = new Scene();
 
-    for (PRenderParams rps = start.pRenderParams(); p_node_valid(rps); rps = rps.pRenderParams())
+    /* If the options block is absent, pOptions() returns a null node and so
+     * does pOptionsItems() on it, so the loop body is skipped. */
+    for (POptionsItems items = start.pOptions().pOptionsItems(); p_node_valid(items); items = items.pOptionsItems())
     {
-        PRenderParam rp = rps.pRenderParam();
+        POptionsItem item = items.pOptionsItem();
         bool ok = true;
-        if (PBackground background = rp.pBackground(); p_node_valid(background))
+        if (PBackground background = item.pBackground(); p_node_valid(background))
         {
             scene->params.background = vector_to_color(background.pVector());
         }
-        else if (PHeight height = rp.pHeight(); p_node_valid(height))
+        else if (PHeight height = item.pHeight(); p_node_valid(height))
         {
             ok = token_to_size(input_file, height.pToken2(), &scene->params.height);
         }
-        else if (PWidth width = rp.pWidth(); p_node_valid(width))
+        else if (PWidth width = item.pWidth(); p_node_valid(width))
         {
             ok = token_to_size(input_file, width.pToken2(), &scene->params.width);
         }