5.2. The .if directive

If-directives work like in standard programming languages. With an .if directive you have the proceeding directive executed only if a given boolean expression is evaluated to true. Here are some examples:

// Set x to 10 if x is higher that 10
.if (x>10) .eval x=10     

// Only show rastertime if the ‘showRasterTime’ boolean is true
.var showRasterTime = false
.if (showRasterTime) inc $d020
jsr PlayMusic
.if (showRasterTime) dec $d020

You can group several statements together in a block with {…} and have them executed together if the boolean expression is true:

// If IrqNr is 3 then play the music
.if (irqNr==3) {
    inc $d020
    jsr music+3
    dec $d020

By adding an else statement you can have an expression executed if the boolean expression is false:

// Add the x’th entry of a table if x is positive or 
// subtract it if x is negative
.if (x>=0) adc zpXtable+x else sbc zpXtable+abs(x)

// Init an offset table or display a warning if the table length is exceeded
.if (i<tableLength) {
   lda #0
   sta offset1+i
   sta offset2+i
} else {
   .error "Error!! I is too high!"