What exactly is the different between "extensible programming" and "extendible programming?"

Wikipedia states the following:

The Lisp language community remained separate from the extensible language community, apparently because, as one researcher observed, any programming language in which programs and data are essentially interchangeable can be regarded as an extendible [sic] language. ... this can be seen very easily from the fact that Lisp has been used as an extendible language for years.

If I'm understanding this correctly, it says "Lisp is extendible implies Lisp is not extensible". So what do these two terms mean, and how do they differ?


3 Answers 3


Wikipedia uses the term extensible throughout the article. The quote from the M. C. Harrison (included in your extract) uses the term extendible. "[sic]" is placed after the first use of "extendible" in the quote to indicate that the word choice is that of the original speaker and not an error in transcription.

This implies to me that the Wikipedia editors did not intend to make any distinction between the two words, but of course they didn't want to change Harrison's quote either. You may also note that the 1960 symposium from which the quote was taken was titled Panel on the Concept of Extensibility, so I think it likely that "extensibility" is the more common choice for this term.

For an interpretation of the intended overall meaning, I would agree with Javier's answer.


I call semantic shenanigans.

Extensible has one meaning: able to be extended. Extendible means the same thing. They are both adjectival forms of extend.

Extend covers a variety of contexts, from mass, to length, to ability.

The difference seems to be (from reading the wiki article) that extensible programming languages use a meta language to alter themselves, whereas extendible languages are modifiable using themselves, and Lisps use the transposability of data and programmes to do that.

  • The correct answer.
    – Den
    Jul 10, 2015 at 9:44

I read it as "Lisp doesn't bother with 'extensible language' works because it's already extensible by design". IOW: the 'extensible language community' is working hard to get what Lisp already has; but without being Lisp.

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