Higher-order functions: Difference between revisions

=={{header|6502 Assembly}}==

For the most part, it's easier to call two functions back to back. However passing functions as arguments can still be done.

Code is called using the following macro, e.g. <code>PrintOutput #$FF,foo</code>. The printing routine is left unimplemented.

<lang 6502asm>macro PrintOutput,input,addr

; input: desired function's input

; addr: function you wish to call

LDA #<\addr ;#< represents this number's low byte

STA z_L

LDA #>\addr ;#> represents this number's high byte

STA z_H

LDA \input

JSR doPrintOutput

endm</lang>

<lang 6502asm>PrintOutput:

; prints the output of the function "foo" to the screen.

; input:

; A = input for the function "foo".

; z_L = contains the low byte of the memory address of "foo"

; z_H = contains the high byte of the memory address of "foo"

pha

LDA z_L

STA smc+1 ;store in the low byte of the operand

LDA z_H

STA smc+2 ;store in the high byte of the operand

pla

smc:

JSR $1234

;uses self-modifying code to overwrite the destination with the address of the passed function.

;assuming that function ends in an RTS, execution will return to this line after the function is done.

JSR PrintAccumulator

rts</lang>