Define macro with .macro and .endm. You can use a parametric macros - any parameter is addressable by %%1, %%2, %%3, ... For example, such code:
.macro decadd
adi %%1
daa
.endm
; Use this macro
decadd $22
will generate this:
0000 ; Use this macro
**MACRO UNROLL - DECADD
0000 87 22 ADI $22
0001 27 DAA
Local labels
Macros has no local label mechanism. So if you define a label in a macro, it unrolls to the same label, ending with a "redefine label" error message.
There is a workaround to define unique label for each macro unrolling:
.macro xyz
loop%%M: inc a
dec b
jr nz,loop%%M
.endm
Now it is safe to use this macro repeatedly, because special placeholder "%%M" is replaced by string "M_"+line number. It provides a good enough workaround for local labels.
Compound parameters
Let's imagine a macro:
.macro test
db %%1
dw %%2
.endm
If you use this macro in such form, everything is OK:
test $12, $3456
Two parameters is OK. But what if you need the first DB is something like db $de,$ad,$be,$ef? You can use the compound parameter:
test {$de,$ad,$be,$ef}, $3456
Rich syntax (v2.5.2+)
A macro can be defined by standard syntax as .macro name, or more consistent way as name: .macro or name .macro.
Formal parameters (v2.5.2+)
Now you can name formal parameters too. For example - assume a macro cpymem for copy memory content. Such macro has three arguments - source, destination and length. The old form of macro has mute parameters, just referenced by its number:
.macro cpymem
LD HL,%%1
LD DE,%%2
LD BC,%%3
LDIR
.endm
New formal parameters, introduced in revision 2.5.2, allows to write this:
.macro cpymem, src, dst, len
LD HL,src
LD DE,dst
LD BC,len
LDIR
.endm
Preprocessor also check if the number of given parameters is sufficient for the macro, i.e. you cannot specify less parameters than formal, like cpymem 100, 200.
All those named parameters are strictly local (in fact, they are replaced with its values before assembly phase).