\ Structural Conditionals, based on branches               12dec92py

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: ?struc      ( flag -- )       abort" unstructured " ;
: sys?        ( sys -- )        dup 0= ?struc ;
: >mark       ( -- sys )        here  0 , ;
: >resolve    ( sys -- )        here over - swap ! ;
: <resolve    ( sys -- )        here - , ;

: BUT       sys? swap ;                      immediate restrict
: YET       sys? dup ;                       immediate restrict

\ Structural Conditionals                              12dec92py

: AHEAD     postpone branch >mark ;           immediate restrict
: IF        postpone ?branch >mark ;          immediate restrict
: THEN      sys? dup @ ?struc >resolve ;     immediate restrict
: ELSE      sys? postpone AHEAD swap postpone THEN ;
                                             immediate restrict

' THEN Alias ENDIF immediate restrict

: BEGIN     here ;                           immediate restrict
: WHILE     sys? postpone IF swap ;           immediate restrict
: AGAIN     sys? postpone branch  <resolve ;  immediate restrict
: UNTIL     sys? postpone ?branch <resolve ;  immediate restrict
: REPEAT    over 0= ?struc postpone AGAIN postpone THEN ;
                                             immediate restrict