Add end-to-end test for CASE/OF/ENDOF/ENDCASE defined in pure Forth

Redefines CASE/OF/ENDOF/ENDCASE using only POSTPONE and IF/ELSE/THEN,
proving these words can be built from lower-level primitives. Tests
basic matching, defaults, empty CASE, return values, nesting, and
computed OF values.

Author: ncw

testdata/end-to-end/case_forth.fth

@@ -0,0 +1,98 @@
+\ Test CASE/OF/ENDOF/ENDCASE redefined in pure Forth
+\ This proves these words can be built on top of IF/ELSE/THEN
+
+\ Redefine CASE words in pure Forth
+: CASE     0 ; IMMEDIATE
+: OF       POSTPONE OVER POSTPONE = POSTPONE IF POSTPONE DROP ; IMMEDIATE
+: ENDOF    POSTPONE ELSE ; IMMEDIATE
+: ENDCASE  POSTPONE DROP  BEGIN ?DUP WHILE POSTPONE THEN REPEAT ; IMMEDIATE
+
+\ Basic CASE with multiple OFs and a default
+: TEST1 ( n -- )
+    CASE
+        1 OF ." one" ENDOF
+        2 OF ." two" ENDOF
+        3 OF ." three" ENDOF
+        ." other"
+    ENDCASE
+;
+
+\ CASE with no default (selector dropped silently)
+: TEST2 ( n -- )
+    CASE
+        1 OF ." yes" ENDOF
+    ENDCASE
+;
+
+\ Empty CASE (just drops the selector)
+: TEST3 ( n -- )
+    CASE ENDCASE
+;
+
+\ CASE returning values from OF branches
+: TEST4 ( n -- m )
+    CASE
+        1 OF 100 ENDOF
+        2 OF 200 ENDOF
+        3 OF 300 ENDOF
+        \ default: selector still on stack, compute result and
+        \ put it under the selector for ENDCASE to DROP
+        DUP 1000 * SWAP
+    ENDCASE
+;
+
+\ Nested CASE
+: TEST5 ( n m -- )
+    SWAP
+    CASE
+        1 OF
+            CASE
+                10 OF ." 1-10" ENDOF
+                20 OF ." 1-20" ENDOF
+                ." 1-?"
+            ENDCASE
+        ENDOF
+        2 OF DROP ." two" ENDOF
+        DROP ." other"
+    ENDCASE
+;
+
+\ CASE with fall-through computation in OF
+: TEST6 ( n -- )
+    CASE
+        3 1+ OF ." four" ENDOF
+        ." nope"
+    ENDCASE
+;
+
+: MAIN
+    \ TEST1: basic matching and default
+    1 TEST1 CR
+    2 TEST1 CR
+    3 TEST1 CR
+    4 TEST1 CR
+
+    \ TEST2: no default
+    1 TEST2 CR
+    5 TEST2 CR
+
+    \ TEST3: empty CASE drops selector
+    42 TEST3
+
+    \ TEST4: returns values
+    1 TEST4 . CR
+    2 TEST4 . CR
+    3 TEST4 . CR
+    7 TEST4 . CR
+
+    \ TEST5: nested CASE
+    1 10 TEST5 CR
+    1 20 TEST5 CR
+    1 99 TEST5 CR
+    2 99 TEST5 CR
+    3 99 TEST5 CR
+
+    \ TEST6: computed OF value
+    4 TEST6 CR
+    5 TEST6 CR
+;

testdata/end-to-end/case_forth.txt

@@ -0,0 +1,17 @@
+one
+two
+three
+other
+yes
+
+100
+200
+300
+7000
+1-10
+1-20
+1-?
+two
+other
+four
+nope