IMP (programming language): Difference between revisions

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'''IMP''' is an early [[Systems programming|systems]] [[programming language]] that was developed by [[Edgar T. Irons]] in the late 1960s through early 1970s, at the [[National Security Agency]] (NSA). Unlike most other systems languages, IMP supports [[Syntax (programming languages)|syntax]]-[[extensible programming]].

Even though {{citation needed span|date=June 2020|reason=While presumably true, the actual quote deserves a specific cite amongst a plethora of similar statements|its designer refers to the language as "being based on [[ALGOL]]"}}, IMP excludes many ''defining'' features of that language, while supporting a very non-ALGOL-like one: syntax extensibility.

A [[compiler]] for IMP existed as early as 1965 and was used to program the [[CDC 6600]] time-sharing system, which was in use at the [[Institute for Defense Analyses]] since 1967. Although the compiler is slower than comparable ones for non-extensible languages, it has been used for practical production work.

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Basically, the syntax statement is an augmented BNF production with associated [[Semantics (computer science)|semantics]] added on the right:

<sourcesyntaxhighlight lang="abnf">

<class> ::= syntax-part ::= semantic-part

</syntaxhighlight>

</source>

For example, to add the construct described by the following BNF:

<sourcesyntaxhighlight lang="abnf">

<EXP> ::= INCREMENT <VBL>

</syntaxhighlight>

</source>

with the semantics that <code>INCREMENT V</code> should translate to <code>V &larr; V + 1</code>, the programmer would only need to insert the following ''IMP statement'':

<sourcesyntaxhighlight lang="abnf">

<EXP> ::= INCREMENT <VBL,A> ::= "A←A+1"

</syntaxhighlight>

</source>

The semantic-part can also contain calls to ''semantic routines'', as in the following syntax statement:

<sourcesyntaxhighlight lang="abnf">

<ATOM> ::= ABS ( <ATOM,A> ) ::= DEWOP(214B,AREG1(1,13),A)

</syntaxhighlight>

</source>

The semantic part of this statement consists of a call on the semantic routine <code>DEWOP</code>. The arguments are the octal constant <code>214B</code>, the semantic routine call <code>AREG1(1,13)</code>, and <code>A</code>, which is the object on top of the stack at the moment this production is invoked. <code>DEWOP</code> is a semantic routine which respectively takes as its arguments a PDP-10 machine language [[opcode]], a register object, and any other object, and produces an object whose value is the result of executing the designated machine instruction using as address field the object which is its last argument. In this example, the opcode <code>214B</code> designates the <code>Load Magnitude</code> instruction, and thus the result of the above syntax statement will be to compile code to compute the absolute value of <code>A</code>.

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==References==

{{Reflist}}

*{{Cite journal |last=Irons |first=Edgar T. |date=January 1970 |title=Experience with an Extensible Language |journal=[[Communications of the ACM]] (CACM) |volume=13 |issue=1 |pages=31–40 |publisher=[[Association for Computing Machinery]]|doi=10.1145/361953.361966 |s2cid=17635545 |doi-access=free }}

*{{Cite journal |last=Bilofsky |first=Walter |date=May 1974 |title=Syntax Extension and the IMP72 Programming Language |journal=SIGPLAN Notices |volume=9 |issue=5 |pages=13–30 |publisher=[[Association for Computing Machinery]] |doi=10.1145/987413.987416 |s2cid=2170981 |via=Yale University}}

==External links==

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[[Category:Extensible syntax programming languages]]

[[Category:Systems programming languages]]

[[Category:National Security Agency]]