SCAN SAVE-INPUT SCR
SCAN ( addr cnt c -- addr' cnt' )  
<FORTH-83-L&P>
scan for first occurence of c in string 
 simulate:
   : SCAN >R BEGIN DUP OVER C@ R@ = 0= OR WHILE 
                    1- SWAP 1- SWAP REPEAT R> DROP ;

reference: p4_scan in ../src/lpf83.c:0248, export CO SCAN