Simple CASE implementation.

common/case.fs

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+\ Copyright 2022 Bradley D. Nelson
+\
+\ Licensed under the Apache License, Version 2.0 (the "License");
+\ you may not use this file except in compliance with the License.
+\ You may obtain a copy of the License at
+\
+\     http://www.apache.org/licenses/LICENSE-2.0
+\
+\ Unless required by applicable law or agreed to in writing, software
+\ distributed under the License is distributed on an "AS IS" BASIS,
+\ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+\ See the License for the specific language governing permissions and
+\ limitations under the License.
+
+: CASE ( n -- ) postpone ahead >r postpone begin
+                postpone ahead r> postpone then swap ; immediate
+: ENDCASE   drop postpone drop postpone then ; immediate
+: OF ( n -- ) postpone over postpone = postpone if ; immediate
+: ENDOF   postpone drop over postpone again postpone then ; immediate