#pragma once, for fasmg / fasm2:

onetime.inc

; We can make a global "#pragma once" mechanism if we assume all files have
; a unique path. Non-cannonical path are fine as long as it's always the same
; form. Be mindful of file organization if you're going to use this.
; Primary benefits:
;	+ files are not loaded multiple times
;	+ no change to file needed (i.e. if/endif wrapper)

;macro onetime?: line&
;	local name
;	match any rest,line
;		name equ any
;	else match any,line
;		name equ any
;	else
;		err
;	end match
;
;	repeat 1,N:name
;		if ~ definite ONCE.N
;			ONCE.N := 1
;			include line
;		end if
;	end repeat
;end macro

calminstruction onetime?: line*&
	match name any?,line
	jyes go
	err 'filename expected'
done:	exit

	local val,var
go:	compute val,+name		; convert string to number
	arrange var,=ONETIME.val	; unique variable
	check definite var
	jyes done

	compute val,0
	publish var:,val		; constant

	arrange line,=include line
	assemble line
end calminstruction

We can replace the include keyword with this feature:

macro include?.enable? chain
	chain
	calminstruction include? file*, head
		local val,var
		compute val,+file		; convert string to number
		arrange var,=INCLUDE.val	; unique variable
		check definite var
		jyes skip

		compute val,0
		publish var:,val		; constant

		arrange line,=include file,=include?.=enable? head
		assemble line
		arrange line,=purge =include?
		assemble line
	skip:
	end calminstruction
end macro
include?.enable?

... based on the fix.inc macros.