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<I><H2>MACRO<BR>
ENDM</H2></I><HR>
<P>One of the best features of an assembler is the ability to write macros for it. Macros also provide a method of passing
arguments to them and they can then react to the input using IF-constructs.<BR>
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<PRE>MyMacro: MACRO
ld a,80
call MyFunc
ENDM</PRE>
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<P>The above example is a very simple macro. You execute the macro by typing its name.<BR>
<BR>
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<PRE> add a,b
ld sp,hl
MyMacro ;This will be expanded
sub a,87</PRE>
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<P>When the assembler meets MyMacro it will insert the macrodefinition (the text enclosed in <B>MACRO/ENDM</B>).
<P><A NAME="labelsuffix"></A>Suppose your macro contains a loop.<BR>
<BR>
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<PRE>LoopyMacro: MACRO
xor a,a
.loop ld [hl+],a
dec c
jr nz,.loop
ENDM</PRE>
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<A TARGET="#labelsuffix"></A><P>This is fine. That is, if you only use the macro once per <A HREF="labels.htm">scope</A>. To get around this problem there is a special label string equate called <B>\@</B> that you can append to your labels and it will then expand to a unique string.
<B>\@</B> also works in <A HREF="rept.htm">REPT-blocks</A> should you have any loops there.<BR>
<BR>
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<PRE>LoopyMacro: MACRO
xor a,a
.loop\@ ld [hl+],a
dec c
jr nz,.loop\@
ENDM</PRE>
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<H4>Arguments</H4>
<P>I'd like <I>LoopyMacro</I> a lot better if I didn't have to pre-load the registers with values and <I>then</I> call it.
What I'd like is the ability to pass it arguments and it then loaded the registers itself.
<P>And I can do that. In macros you can get the arguments by using the special macro string equates <B>\1</B> through
<B>\9</B>, <B>\1</B> being the first argument specified on the calling of the macro.<BR>
<BR>
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<PRE>LoopyMacro: MACRO
ld hl,\1
ld c,\2
xor a,a
.loop\@ ld [hl+],a
dec c
jr nz,.loop\@
ENDM</PRE>
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<P>Now I can call the macro specifying two arguments. The first being the address and the second being a bytecount.
The macro will then reset all bytes in this range.<BR>
<BR>
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<PRE> LoopyMacro MyVars,54</PRE>
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<P> You can specify up to nine arguments when calling a
macro. Arguments are passed as string equates. There's no need to enclose them in quotes. Parameter passing has changed a bit since v1.03 in that an expression will not be evaluated first but passed directly. This means that it's probably a very good idea to use
brackets around \1-\9 if you perform further calculations on them. For instance if you pass 1+2 as the first argument and then do
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<PRE> PRINTV \1*2
</PRE>
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you will get the value 5 on screen and not 6 as you might have expected..<BR>
<P>Note that a colon (:) following the macro-name is required. Macros can't be exported or imported. It's valid to call a macro from a macro (yes, even the same one).<BR>
<H3>See also:</H3>
<UL>
<LI><A HREF="shift.htm">SHIFT</A>
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<BR><HR>
<FONT SIZE="-1"><I><P ALIGN=RIGHT>Last updated 02 July 1997 by <A HREF="mailto:[email protected]">Carsten Sorensen</A></P></I></FONT>