Editing Assembly language (section)

===Support for structured programming===
<!-- With rare exceptions, macros are not part of the assembler but reside in the source code or in macro libraries. -->
Packages of macros have been written providing [[structured programming]] elements to encode execution flow. The earliest example of this approach was in the [[Concept-14 macro set]],<ref name="Kessler_1970"/> originally proposed by [[Harlan Mills]] (March 1970), and implemented by Marvin Kessler at IBM's Federal Systems Division, which provided IF/ELSE/ENDIF and similar control flow blocks for OS/360 assembler programs. This was a way to reduce or eliminate the use of [[GOTO]] operations in assembly code, one of the main factors causing [[spaghetti code]] in assembly language. This approach was widely accepted in the early 1980s (the latter days of large-scale assembly language use). IBM's High Level Assembler Toolkit<ref>{{cite web
 |     title = High Level Assembler Toolkit Feature Increases Programmer Productivity
 |        id = A95-1432
 |      date = December 12, 1995
 |       url = https://www.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/2/649/ENUSA95-1432/index.html&request_locale=en
 | work      = Announcement Letters
 | publisher = [[IBM]]
 | archive-url = https://web.archive.org/web/20230307045942/https://www.ibm.com/common/ssi/ShowDoc.wss?docURL=/common/ssi/rep_ca/2/649/ENUSA95-1432/index.html&request_locale=en
 | archive-date = March 7, 2023
 | url-status = dead
 }}
</ref> includes such a macro package.

Another design was [[A-Natural]],<ref>{{Cite book |last=Whitesmiths Ltd |url=http://archive.org/details/a-natural-manual |title=A-Natural Language Reference Manual |date=1980-07-15}}</ref> a "stream-oriented" assembler for 8080/[[Zilog Z80|Z80]] processors from [[Whitesmiths|Whitesmiths Ltd.]] (developers of the [[Unix]]-like [[Idris (operating system)|Idris]] operating system, and what was reported to be the first commercial [[C (programming language)|C]] [[compiler]]). The language was classified as an assembler because it worked with raw machine elements such as [[opcode]]s, [[processor register|registers]], and memory references; but it incorporated an expression syntax to indicate execution order. Parentheses and other special symbols, along with block-oriented structured programming constructs, controlled the sequence of the generated instructions. A-natural was built as the object language of a C compiler, rather than for hand-coding, but its logical syntax won some fans.

There has been little apparent demand for more sophisticated assemblers since the decline of large-scale assembly language development.<ref name="assembly-language?cat=technology"/> In spite of that, they are still being developed and applied in cases where resource constraints or peculiarities in the target system's architecture prevent the effective use of higher-level languages.<ref name="Provinciano_2005"/>

Assemblers with a strong macro engine allow structured programming via macros, such as the switch macro provided with the Masm32 package (this code is a complete program):

<syntaxhighlight lang="nasm">
include \masm32\include\masm32rt.inc	; use the Masm32 library

.code
demomain:
  REPEAT 20
	switch rv(nrandom, 9)	; generate a number between 0 and 8
	mov ecx, 7
	case 0
		print "case 0"
	case ecx				; in contrast to most other programming languages,
		print "case 7"		; the Masm32 switch allows "variable cases"
	case 1 .. 3
		.if eax==1
			print "case 1"
		.elseif eax==2
			print "case 2"
		.else
			print "cases 1 to 3: other"
		.endif
	case 4, 6, 8
		print "cases 4, 6 or 8"
	default
		mov ebx, 19		     ; print 20 stars
		.Repeat
			print "*"
			dec ebx
		.Until Sign?		 ; loop until the sign flag is set
	endsw
	print chr$(13, 10)
  ENDM
  exit
end demomain
</syntaxhighlight>