\ Copyright 2021 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. 
 
( Interpret time conditionals ) 
 
: DEFINED? ( "name" -- xt|0 ) 
   begin bl parse dup 0= while 2drop refill 0= throw repeat 
   find state @ if aliteral then ; immediate 
defer [SKIP] 
: [THEN] ; immediate 
: [ELSE] [SKIP] ; immediate 
: [IF] 0= if [SKIP] then ; immediate 
: [SKIP]' 0 begin postpone defined? dup if 
    dup ['] [IF] = if swap 1+ swap then 
    dup ['] [ELSE] = if swap dup 0 <= if 2drop exit then swap then 
    dup ['] [THEN] = if swap 1- dup 0< if 2drop exit then swap then 
  then drop again ; 
' [SKIP]' is [SKIP] 
 

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