What is the history of the term "metasyntactic variable"?

Question

Background

A metasyntactic variable is a word or term that stands in for something else, typically used when you're describing an overall pattern, and the subject under discussion could have any name in actual practice. A placeholder.

It's most commonly used in computer science and related fields, and in that community foo is the most commonly used and recognized metasyntactic variable.

Example

The classic example from the C2 Wiki:

Suppose I have a list, foo, with a node, bar, ...

What this allows us to do is now refer to the list as "foo" and and the node as "bar", as in "now, if bar is the last node in foo...", while recognizing that in a program the real "foo" and "bar" could have any name at all.

Origins

But here, I'm not asking about "foo" or "bar"¹ or any specific metasyntactic variable, I'm asking about the term metasyntactic variable.

A recent answer on a different question suggested the author Terry Pratchett could have invented it:

Terry Pratchett .. used the idea of a 'Metasyntactic variable' (his own nomenclature I believe but open to correction).

Pratchett didn't invent the term, but the answer prompted me to look into who did, and I'm stumped.

So:

1. When was the term metasyntactic variable first used, or metasyntactic modifying some other word, giving the same meaning?
2. Why meta-syntactic?
3. Was there any specific event or author who popularized it, or was its growth simply organic?
4. Is the term used with the same meaning in any interesting ways outside of the software world (like the Terry Pratchett example)?

Early uses

Using Google Books and Google nGrams², the earliest use of the full term metasyntactic variable I could find was the 1979 work The MDL Programming Language, which reads, on page 4:

A metasyntactic variable -- something to be replaced in actual use by something else -- appears as a radix:fix, in an italic font; often the variable will have both a meaning and a data type (as here), but sometimes those will be omitted, for obvious reasons.

and on page 44:

TYPE (aren't homonyms wonderful?), just type the appropriate ATOM, like FIX or FLOAT or ATOM etc. However, in this document we will use the convention that a metasyntactic variable can have a type for a "data type": for example, foo:type means that the TYPE of foo is ATOM, but the ATOM must be something that the SUBR TYPE can return.

These paragraphs suggest, respectively, that (a) the term is new enough that it has to be defined (a 1990 Emacs Lisp manual uses the word unselfconsicously and without any definition, because by then everyone knew what it meant), and (b) that it's established enough that the authors have to defend their novel convention that m.v.s may have data types (which is atypical).

Which means this may be an early use, but not the first use.

So, broadening my search, and looking for only metasyntactic, I found ALGOL-Bulletin no. 13, published August 1961, mentioning a memo written in November 1960 which used that word:

But it's not clear whether this metasyntactic had the same sense as it does in the full term metasyntactic variable, as the word "classes" suggest this might be a more specific and technical term of art in ALGOL's design, or computer language design more broadly.

"Meta" syntactic

Aside from its first use, I'm interested in why the term "metasyntactic" was chosen in the first place. What is "meta" about these terms' relationship to syntax?

The canonical source on this, The Jargon File, presents three different concepts (list-ified for clarity):

Metasyntactic variables are so called because

1. They are variables in the metalanguage used to talk about programs etc.
2. They are variables whose values are often variables (as in usages like “the value of f(foo,bar) is the sum of foo and bar”).
3. However, it has been plausibly suggested that the real reason for the term “metasyntactic variable” is that it sounds good.

In addition, I've personally made the argument that their meta-syntacticness arises from the fact that the same words can be used to stand in for any part of speech.

In any case, while (1) or some version of it is probably the first idea that would come to most people's minds, the fact that the Jargon File didn't stop there is telling, and I think finding the origins of the term will shed a lot of light here.

Non-software uses or origins

The Terry Pratchett answer above also got me thinking: do non-computer scientists use the term metasyntactic variable, in a non-software context? Are there people who use this term non-ironically, who are not familiar with its software sense?

I would be particularly interested in answers which show the term pre-dates its use in software. Given that "syntax" is really only studied by one other group, I wonder do linguists or syntacticians of natural languages³ use this term at all? Did they do so before, say, 1950?

---

¹ _{Interestingly, foo and bar have their own, detailed etymology, and no, it's not as straightforward as "arising from the WWII acronym FUBAR". See RFC 3092 and the canonical post about foo here on EL&U.}

² _{I actually was forced to use only Google Books for the full term; for some reason, metasyntactic variable doesn't show up in nGram Viewer at all.}

³ _{I once made the case that words like "thingy", "doodad", "whatshisface", etc are "metasyntactic variables", but John Lawler says they're more properly termed "nonce forms" by linguists.}

_{PS: I know I've picked the low-hanging fruit here, with Google Books and Google nGram Viewer, but I would really still prefer scholastic, detailed answers. Speculation will just add noise. Though I'm also happy to accept first-hand accounts from people who lived through the 50s-60s-70s computer era (or very credible second-hand accounts).}

Answer 1

Ingerman and Sattley 1960

I decided to pull on the thread of use of metasyntactic by Ingerman and Sattley in their November 1960 memo.

Knuth 1961

Searching for their names in relation to the language name ALGOL quickly revealed an abstract of a paper by Knuth titled ALGOL 60 confidential, written June 1961, which uses the word metalinguistic:

The ALGOL 60 Report, when first encountered, seems to describe a very complex language which will be difficult to learn. The “metalinguistic formulae” admirably serve the purpose of precisely specifying a language, but they are certainly not very readable for a beginner.

Following that lead and searching for the term "metalinguistic formulae" in relation to Knuth, we find Development, Assessment, and Reengineering of Language Descriptions by Alex Sellink and Chris Verhoef, undated but from its bibiliography no earlier than 1999:

In his paper on the syntax and semantics of the proposed international algebraic language, Backus [2] writes: `we shall need some metalinguistic conventions for characterizing various strings of symbols. To begin, we shall need metalinguistic formulae.' Then he introduced using an example what is now widely known as the Backus-Naur Formalism.

Backus 1959

And the light begins to dawn. Backus-Naur Form is the famous notation for describing computer languages. That is, it is a language for describing languages: a metalanguage. Note that the ALGOL Bulletin where we found the earliest use of metasyntactic is in fact compiled by Naur, who co-created the Backus-Naur form.

So, chasing down Sellink and Verhoef's reference [2], we find Backus' The Syntax and Semantics of the Proposed International Algebraic Language of the Zurich ACM-GAMM Conference., written 1959:

Syntax of IAL

In the description of IAL syntax which follows we shall need some metalinguistic conventions for characterizing various strings of symbols. To begin, we shall need metalinguistic formulas. Their interpretation is best explained by an example:

This use of metalinguistic formulas was enthusiastically quoted by Knuth, by Sellink and Verhoef, by several other authors and papers I encountered in this search, and the very wording is emphasized in the relevant Wikipedia article.

Similarly, the Wikipedia article quotes Naur, two years later, in 1961:

The meaning of syntactic formula may be further explained by saying that words enclosed in the brackets < >, like <ab>, denote classes whose members are sequences of basic symbols. Class designations of this kind are found in any description of a language. For describing ordinary natural languages designation like word, verb, noun, are used. Peter Naur (1961)."A COURSE ON ALGOL PROGRAMMING". p. 5, Note 1. Retrieved 26 March 2015.

So it seems it was Backus' use of metalinguistic that galavanized and motivated its use in the early computer industry, and likely inspired the related word metasyntactic used by Ingerman and Sattley, who moved in the same circles.

From "metasyntactic" to "metasyntactic variables"

I haven't yet been able to hunt down the first use of "metasyntactic variable" as applied to terms like "foo" and "bar" but it now seems inescapable that it developed out of the use of metalinguistic formulas as coined by Backus in 1959.

This coinage was adopted in the ALGOL community in the 1960s, to grew to the extent that the "variable" term was applied and understood more broadly in language design circles by no later than the late 1970s (as used by Galley and Pfister in the MDL Language book in the question; MDL was a derivative of LISP, another early programming language).

If I can find a more direct connection, or fill in a few more of the missing links, I will update this answer.

Answer 2

With a hyphen, I first see "meta-syntactic variable" being used in Software 71: proceedings of a conference sponsored by Software World and held at the University of Kent at Canterbury, July 1971:

Here 'TYPE' and "MODE" are meta-syntactic variables such as used in the definition of ALGOL 68 [reference 3].

R3 TYPE--> procedure | data-structure

Where reference 3 is VAN WYNGAARDEN, A., MAILLOUX, B.J. , PECK, J.E.L., and KOSTER, C.H.A., 'Draft report on the algorithmic language ALGOL 68', Amsterdam Mathematisch Centrum.

Without a hyphen "metasyntactic variable" is used in the May 1972 thesis of Michael Kelly Donegan, CODE GENERATION FOR NEW ON THE RICE RESEARCH COMPUTER. The word "NEW" is underlined in the title and refers to the computer language NEW.

VARIABLE assignation: reference destination, becomes symbol, value source.

The semantic interpretation of the assignation is embodied in the syntax by asserting that the destination is to be elaborated in reference mode and the source in value mode. VARIABLE is a metasyntactic variable whose rule is

VARIABLE: reference; value.

This asserts, in the case of assignations, that the value of an assignation may have two interpretations. The value in reference mode is the value of the destination, while in value mode it is the value of the source.

The plural form "metasyntactic variables" is used in the 1975 book The structure and design of programming languages

The term "syntactic variable" had been in use since about 1950 in the symbolic logic and computer fields.

See for example the 1959 Journal of the Association for Computing Machinery which has a footnote:

Note that the symbols p1, p2, etc. occur here as "syntactic variables." That is, they stand for expressions made up of our symbols.