"foop": a naming convention? It's a helper recursive function for "foo"; what does the suffix "p" mean?

Question

I've come across the following code snippet (a function definition):

choose (x:xs) = choosep x xs
  where choosep x [] = x
        choosep x (_:_) = x
        choosep _ (x:xs) = choosep x xs

in Curry programming language in a "standard library"--/usr/lib/curry-0.9.11/Success.curry from Muenster Curry Compiler. Here:

choose :: [a] -> a

and

choosep :: a -> [a] -> a -- BTW, not a _p_redicate

Is the "p" suffix for the helper recursive function choosep a known naming convention? Perhaps it comes from functional programming tradition (Haskell) or logical programming (Prolog?). What does it mean then?

(This function was considered in Why is the non-deterministic choice function in Curry's std lib not defined straightforwardly but rather with a helper 2-argument function?.)

score 2 · Answer 1 · answered Mar 11 '11 at 23:05

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In this case, I believe p stands for "prime". Rather than calling the helper choose' or chooseprime, they use choosep.

answered Mar 11 '11 at 23:05

Gabe

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Yes, this seems to be plausible. `'` would be clearer than `p` ;) – imz -- Ivan Zakharyaschev Mar 11 '11 at 23:16

phooji · Answer 2 · 2011-03-11T23:14:09.923

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I think it stands for 'prime' -- in OCaml, which allows ' in identifiers, helper functions are frequently named foo'. At a high level, I think this (and the use of 'where' for a post-hoc helper definition) stems from the desire to allow functional programs to resemble their equivalent definitions in pure math.

edited Mar 11 '11 at 23:14

answered Mar 11 '11 at 23:08

phooji

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As far as I can tell, the Muenster Curry compiler also allows `'` in identifiers. – Gabe Mar 11 '11 at 23:20
Yes, it's a very nice thing about names in these languages--that they allow to write primes at the end, so that it looks like math. I was glad when I saw it the first time when learning Haskell. And well, Curry also allows the more real prime symbols (`'`) in names, and there are primes in variable names in other "standard" modules' implementations. (Out of curiosity, I'll perhaps look whether there are occurences of `'` in *function* names.) So, the way to this "p" is somewhat strange: write out a `'` as `prime`, then abbreviate it to `p`... ;) – imz -- Ivan Zakharyaschev Mar 11 '11 at 23:29
@Gabe: Path dependence then :) – phooji Mar 11 '11 at 23:31
@imz: Perhaps the only way to be sure is to email this guy: http://www.informatik.uni-kiel.de/~mh/ ? – phooji Mar 11 '11 at 23:33
True. Ok, if it's not a well-known naming convention, then I'll probably not bother. – imz -- Ivan Zakharyaschev Mar 11 '11 at 23:37

score 1 · Answer 3 · answered Mar 11 '11 at 23:15

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In this context, as others have noted, it probably doesn't apply, but there is a popular Lisp convention of using a final 'p' to denote a predicate. See jargon p-convention.

I personally prefer the Ruby convention of ending a predicate with a '?'.

answered Mar 11 '11 at 23:15

Don Roby

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Thanks for the comment! That's why it looked kinda misleading: a `p` sticked not to a predicate... – imz -- Ivan Zakharyaschev Mar 11 '11 at 23:19
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Ending predicate names with `?` is a convention in many Lisps (and some relatives like Scheme and Logo) as well. Common Lisp, unfortunately, does not follow. – ephemient Mar 12 '11 at 01:42

score 0 · Answer 4 · answered Mar 11 '11 at 23:04

0

P stands for 'predicate'. A thing that returns 'true' or 'false'.

answered Mar 11 '11 at 23:04

bmargulies

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That's what I thought at first, but in this case the function isn't a predicate. – Gabe Mar 11 '11 at 23:07
Yes, `choose`'s type is `[a] -> a`, not a predicate. And `choosep :: a -> [a] -> a`. – imz -- Ivan Zakharyaschev Mar 11 '11 at 23:09
Well, this is very interesting. There's a longstanding tradition of 'foop' as foo-predicate all over other areas, these haskellers are just odd. – bmargulies Mar 11 '11 at 23:51

"foop": a naming convention? It's a helper recursive function for "foo"; what does the suffix "p" mean?

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