Write sufficient tests (I think) for analysis of ifs.

README.markdown

@@ -31,7 +31,7 @@ TODO
 
 For 0.2:
 
-*   analyze `if` correctly.
+*   write a few more tests and clean up spec a bit.
 
 For 0.3:
 

src/sixtypical/analyzer.py

@@ -22,6 +22,10 @@ class UninitializedOutputError(StaticAnalysisError):
     pass
 
 
+class InconsistentInitializationError(StaticAnalysisError):
+    pass
+
+
 class IllegalWriteError(StaticAnalysisError):
     pass
 
@@ -173,9 +177,9 @@ def analyze_instr(instr, context, routines):
         analyze_block(instr.block1, context1, routines)
         analyze_block(instr.block2, context2, routines)
         for ref in context1.each_initialized():
-            context2.assert_initialized(ref)
+            context2.assert_initialized(ref, exception_class=InconsistentInitializationError)
         for ref in context2.each_initialized():
-            context1.assert_initialized(ref)
+            context1.assert_initialized(ref, exception_class=InconsistentInitializationError)
         context.set_from(context1)
     else:
         raise NotImplementedError(opcode)

src/sixtypical/parser.py

@@ -165,6 +165,8 @@ class Parser(object):
             block2 = None
             if self.scanner.consume('else'):
                 block2 = self.block()
+            else:
+                block2 = Block(instrs=[])
             return Instr(opcode='if', dest=None, src=src, block1=block1, block2=block2)
         elif self.scanner.token in ("ld", "add", "sub", "cmp", "and", "or", "xor"):
             opcode = self.scanner.token

tests/SixtyPical Analysis.md

@@ -413,3 +413,60 @@ Both blocks of an `if` are analyzed.
     |     }
     | }
     = ok
+
+If a location is initialized in one block, is must be initialized in the other as well.
+
+    | routine foo
+    |   inputs a
+    |   outputs x
+    |   trashes a, z, n, c
+    | {
+    |     cmp a, 42
+    |     if z {
+    |         ld x, 7
+    |     } else {
+    |         ld a, 23
+    |     }
+    | }
+    ? InconsistentInitializationError: x
+
+    | routine foo
+    |   inputs a
+    |   outputs x
+    |   trashes a, z, n, c
+    | {
+    |     cmp a, 42
+    |     if z {
+    |         ld a, 6
+    |     } else {
+    |         ld x, 7
+    |     }
+    | }
+    ? InconsistentInitializationError: x
+
+An `if` with a single block is analyzed as if it had an empty `else` block.
+
+    | routine foo
+    |   inputs a
+    |   outputs x
+    |   trashes a, z, n, c
+    | {
+    |     cmp a, 42
+    |     if z {
+    |         ld x, 7
+    |     }
+    | }
+    ? InconsistentInitializationError: x
+
+    | routine foo
+    |   inputs a
+    |   outputs x
+    |   trashes a, z, n, c
+    | {
+    |     ld x, 0
+    |     cmp a, 42
+    |     if z {
+    |         ld x, 7
+    |     }
+    | }
+    = ok