cmp can compare against a literal word.

HISTORY.md

@@ -10,7 +10,8 @@ History of SixtyPical
 *   When the range of a location is known, `inc` and `dec`
     on it will usually shift the known instead of invalidating it.
 *   `cmp` instruction can now perform a 16-bit unsigned comparison
-    of `word` memory locations (at the cost of trashing `a`.)
+    of `word` memory locations and `word` literals (at the cost of
+    trashing the `a` register.)
 *   Fixed pathological memory use in the lexical scanner - should
     be much less inefficient now when parsing large source files.
 *   Reorganized the examples in `eg/rudiments/` to make them

src/sixtypical/compiler.py

@@ -402,6 +402,16 @@ class Compiler(object):
             self.emitter.emit(CMP(Absolute(Offset(src_label, 1))))
             self.emitter.resolve_label(end_label)
             return
+        if isinstance(src, ConstantRef) and src.type == TYPE_WORD:
+            dest_label = self.get_label(dest.name)
+            self.emitter.emit(LDA(Absolute(dest_label)))
+            self.emitter.emit(CMP(Immediate(Byte(src.high_byte()))))
+            end_label = Label('end_label')
+            self.emitter.emit(BNE(Relative(end_label)))
+            self.emitter.emit(LDA(Absolute(Offset(dest_label, 1))))
+            self.emitter.emit(CMP(Immediate(Byte(src.low_byte()))))
+            self.emitter.resolve_label(end_label)
+            return
         cls = {
             'a': CMP,
             'x': CPX,

tests/SixtyPical Analysis.md

@@ -1207,6 +1207,28 @@ Some rudimentary tests for `cmp`.
     | }
     ? UnmeaningfulReadError: zb
 
+`cmp` can compare against a literal word.
+
+    | word za
+    | 
+    | define main routine
+    |   inputs za
+    |   trashes a, z, c, n
+    | {
+    |     cmp za, 4000
+    | }
+    = ok
+
+    | word za
+    | 
+    | define main routine
+    |   inputs za
+    |   trashes z, c, n
+    | {
+    |     cmp za, 4000
+    | }
+    ? ForbiddenWriteError: a
+
 ### and ###
 
 Some rudimentary tests for `and`.

tests/SixtyPical Compilation.md

@@ -395,15 +395,21 @@ Compiling 16-bit `cmp`.
     |   trashes a, z, c, n
     | {
     |     cmp za, zb
+    |     cmp za, 4000
     | }
     = $080D   LDA $EA61
-    = $0810   CMP $081C
+    = $0810   CMP $0828
     = $0813   BNE $081B
     = $0815   LDA $EA62
-    = $0818   CMP $081D
-    = $081B   RTS
-    = $081C   .byte $BB
-    = $081D   .byte $0B
+    = $0818   CMP $0829
+    = $081B   LDA $EA61
+    = $081E   CMP #$0F
+    = $0820   BNE $0827
+    = $0822   LDA $EA62
+    = $0825   CMP #$A0
+    = $0827   RTS
+    = $0828   .byte $BB
+    = $0829   .byte $0B
 
 Compiling `if`.