I confess I am a minimalist. Been coding Haskell for a year after a break (my 1982 dissertation was “Optimization of Functional Programs” so my interest goes back a ways). Were I the God of Haskell I would go down the above-mentioned synonym list and deprecate all the less-general “return” things.
I confess also that the semantics of “pure” seems in some cases ((,), etc) to have been chosen for pragmatic reason; inevitably one must choose an embedding when there is a choice, and “I got there first” can be justified if it produces lots of elegant simplicity. To my taste it’s too bad that Collection means “ordered collection” but I imagine that there are more applications in which deterministic iteration is useful.
All that being said, I vote for singleton as a readable method name for Collection instances.
To my way of thinking this implies picking a Collection class and moving it closer to the Root of all Haskell.
Sven Panne wrote:
> Code is mainly *read*, not written, so the less you need
> to know to read and understand code, the better it is.
Yes, and this is an argument *for* singleton, not against:
1. singleton is already known to the Haskell reader from the other
collection types.
2. singleton is unambiguously invoking the image of creating a singleton
collection.
In contrast, "pure" invokes the image of creating a effect-free monadic
computation. (:[]) invokes the image of a (mechanical) gorilla smiling
at you. ;-) All these associations distract from reading the code. In
both cases, a mental translation step is needed:
a) In the case of "pure", the conscious intervention that here we are
not concerned with non-determinism (the list monad), but just creating a
singleton collection.
b) In the case of "(:[])", the conscious intervention consists of
- recognizing the decomposition (: [])
- recognizing the operator section
- understanding it as "cons something to the empty list"
- understanding this as creating a singleton collection.
Both interventions hamper the flow of reading.
Of course, the procedure b) becomes automatic with use. However, it is
still a significant barrier to the newcomer.
Cheers,
Andreas
P.S.: if the gorilla (:[]) is vanishing from the Agda code base, I am
mostly to be blamed for this.
On 2019-08-14 21:51, Sven Panne wrote:
> Am Mi., 14. Aug. 2019 um 21:35 Uhr schrieb Oliver Charles
> <ollie@ocharles.org.uk <mailto:ollie@ocharles.org.uk>>:
>
> I'd also be interested in a kind of "reverse" argument - *if* we had
> this added, what are the costs? There are arguments of "no,
> pure/robot ninja is enough" - fine, we're not taking those away so
> you aren't required to use singleton But what is the *downside* of
> having singleton? [...]
>
>
> A similar argument comes up with basically every extension, and it is a
> very weak one. Code is mainly *read*, not written, so the less you need
> to know to read and understand code, the better it is. Lots of different
> ways to do the same thing makes programs harder to understand, and you
> ultimately end up with Perl. :-} And if we take this argument
> seriously, we should probably add "doubleton" (synonym for "replicate
> 2"), "tripleton" (synonym for "replicate 3"), etc., too. Hey, you don't
> have to use it after all, we're not taking away "replicate"...
>
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