' This function replaces every instances of
' string A$ with string B$. Returns a new string.
' The replacement is case sensitive.
'
' Example:
'
'  REPLACE$("AAABACBAABACA", "BAC", "") --> "AAABAAA"
'
'  REPLACE$("Yes = Si", "s", "sss") --> "Yesss = Si"
'
'  REPLACE$("forever", "for", "n") --> "never"
'
FUNCTION REPLACE$ (S$, A$, B$)
    LA = LEN(A$)
    LB = LEN(B$)
    IF LA = 0 OR LEN(S$) < LA THEN
        REPLACE$ = S$
        EXIT FUNCTION
    END IF
    LENGAIN = LB - LA
    PTR = 1
    X$ = S$
    DO
        F = INSTR(PTR, X$, A$)
        IF F = 0 THEN EXIT DO
        IF LENGAIN < 1 THEN MID$(X$, F) = B$
        IF LENGAIN < 0 THEN X$ = MID$(X$, 1, F + LB - 1) + MID$(X$, F + LA)
        IF LENGAIN > 0 THEN X$ = MID$(X$, 1, F - 1) + B$ + MID$(X$, F + LA)
        PTR = F + LB
    LOOP
    REPLACE$ = X$
END FUNCTION