Correctly analyze repeat { ... } forever loops.

HISTORY.md

@@ -9,6 +9,7 @@ History of SixtyPical
     in a `copy` to a vector is a routine that is defined further down in the source.
 *   Fixed bug which was preventing `if` branches to diverge in what they initialized,
     if it was already initialized when going into the `if`.
+*   Fixed a bug which was making it crash when trying to analyze `repeat forever` loops.
 
 0.9
 ---

eg/proto-game.60p

@@ -240,8 +240,6 @@ routine main
         copy cinv, save_cinv
         copy our_cinv, cinv
     }
-    // FIXME: find out why `repeat { } forever` does not analyze OK
-    repeat {
-        ld a, 0
-    } until not z
+
+    repeat { } forever
 }

src/sixtypical/analyzer.py

@@ -324,12 +324,14 @@ class Analyzer(object):
             # it will always be executed at least once, so analyze it having
             # been executed the first time.
             self.analyze_block(instr.block, context)
-            context.assert_meaningful(src)
+            if src is not None:  # None indicates 'repeat forever'
+                context.assert_meaningful(src)
 
             # now analyze it having been executed a second time, with the context
             # of it having already been executed.
             self.analyze_block(instr.block, context)
-            context.assert_meaningful(src)
+            if src is not None:
+                context.assert_meaningful(src)
 
         elif opcode == 'copy':
             # 1. check that their types are compatible

src/sixtypical/compiler.py

@@ -307,7 +307,7 @@ class Compiler(object):
         elif opcode == 'repeat':
             top_label = self.emitter.make_label()
             self.compile_block(instr.block)
-            if src is None:
+            if src is None:  # indicates 'repeat forever'
                 self.emitter.emit(JMP(Absolute(top_label)))
             else:
                 cls = {

tests/SixtyPical Analysis.md

@@ -1195,6 +1195,15 @@ this is an error too.
     | }
     ? UnmeaningfulReadError: z in main
 
+The body of `repeat forever` can be empty.
+
+    | routine main
+    | {
+    |     repeat {
+    |     } forever
+    | }
+    = ok
+
 ### copy ###
 
 Can't `copy` from a memory location that isn't initialized.

tests/SixtyPical Compilation.md

@@ -297,6 +297,16 @@ Compiling `repeat forever`.
     = $0810   JMP $080F
     = $0813   RTS
 
+The body of `repeat forever` can be empty.
+
+    | routine main
+    | {
+    |     repeat {
+    |     } forever
+    | }
+    = $080D   JMP $080D
+    = $0810   RTS
+
 Indexed access.
 
     | byte one