Re-root site.

common/conditionals.fs

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+\ 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 )
+   bl parse find state @ if aliteral then ; immediate
+defer [SKIP]
+: [THEN] ;   : [ELSE] [SKIP] ;   : [IF] 0= if [SKIP] then ;
+: [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]