$MACRO LEN string
?? 2
	mov #@{1},r0
#@2=.
	tstb (r0)+
	bne #@2
	sub #@{1},r0
	dec r0
$ENDM
/
        PROGRAM pos
        AUTO lin lof ncmp i
        FUNCTION pos[in,of,st]
        LEN in
        mov r0,lin(r5)
        LEN of
        mov r0,lof(r5)
        IF lin LT st  OR  lof GT lin  OR  lof LE #0
            RET #0
        FI 
                       
        LET ncmp = lin - lof + #1
        LOOP for i = #1 TO ncmp
            IF i GE st
                . eq[in,of,lof]
                IF r0 NE #0
                    RET i
                FI 
            FI 
            inc in(r5)
        NEXT i
        RET #0
                       
        .end