Editing Macro (computer science) (section)

==Macros for machine-independent software==
Macros are normally used to map a short string (macro invocation) to a longer sequence of instructions. Another, less common, use of macros is to do the reverse: to map a sequence of instructions to a macro string. This was the approach taken by the [[STAGE2|STAGE2 Mobile Programming System]], which used a rudimentary macro compiler (called SIMCMP) to map the specific instruction set of a given computer into ''machine-independent'' macros. Applications (notably compilers) written in these machine-independent macros can then be run without change on any computer equipped with the rudimentary macro compiler. The first application run in such a context is a more sophisticated and powerful macro compiler, written in the machine-independent macro language. This macro compiler is applied to itself, in a [[Bootstrapping (computing)|bootstrap]] fashion, to produce a compiled and much more efficient version of itself. The advantage of this approach is that complex applications can be ported from one computer to a very different computer with very little effort (for each target machine architecture, just the writing of the rudimentary macro compiler).<ref>{{cite journal |last1=Orgass |first1=Richard J. |last2=Waite |first2=William M. |date=September 1969 |title=A base for a mobile programming system |journal=Communications of the ACM |location=New York, NY, USA |publisher=ACM |volume=12 |issue=9 |pages=507–510 |doi=10.1145/363219.363226 |s2cid=8164996 |doi-access=free}}</ref><ref>{{cite journal | last = Waite | first = William M. | title = The mobile programming system: STAGE2 | journal = Communications of the ACM | volume = 13 | issue = 7 | pages = 415–421 | publisher = ACM | location = New York, NY, USA | date = July 1970 | doi = 10.1145/362686.362691
| s2cid = 11733598 }}</ref> The advent of modern programming languages, notably [[C (programming language)|C]], for which compilers are available on virtually all computers, has rendered such an approach superfluous. This was, however, one of the first instances (if not the first) of [[Bootstrapping (compilers)|compiler bootstrapping]].