Re: Why does "clojure.core/run!" end in an exclamation mark?

[Francis Avila]

doseq is a macro that accepts comprehension clauses like "for", so doseq is 
a straight translation of for that is eager (but still uses seqs 
internally) and swallows its body's results.

run! is like more like (doall (map f xs)), except it swallows results and 
uses "reduce" for speed and efficiency (no seq allocations).

In general, if I am side-effecting at the end of a ->> threading macro 
pipeline, I use run!. If I care about speed I use run! Otherwise I use 
doseq because it looks and feels more "statement-y" to me.


On Saturday, December 24, 2016 at 12:16:50 PM UTC-6, Shantanu Kumar wrote:
>
> I'm curious about `clojure.core/run!` too, but my question is whether it 
> is meant to be a `reduce` variant of `clojure.core/doseq` or it has some 
> other purpose.
>
> Shantanu
>
> On Saturday, 24 December 2016 21:37:11 UTC+5:30, James Reeves wrote:
>>
>> My understanding is that the convention used in clojure.core is to put an 
>> exclamation mark onto the end of any function unsafe to run in a 
>> transaction.
>>
>> Does the reasoning differ for "run!" or is it assumed that the function 
>> passed to "run!" will not usually be idempotent?
>>
>> - James
>>
>

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Re: Why does "clojure.core/run!" end in an exclamation mark?

[James Reeves]

On 25 December 2016 at 10:30, Paulus Esterhazy  wrote:

> The following fn names in clojure.core contain an exclamation mark:
>
> "vswap!" "vreset!" "set-error-mode!" "set-agent-send-executor!"
> "disj!" "conj!" "pop!" "compare-and-set!" "reset-meta!"
> "set-error-handler!" "set-agent-send-off-executor!" "dissoc!" "assoc!"
> "reset!" "alter-meta!" "persistent!" "run!" "set-validator!" "swap!"
> "volatile!" "io!"
>
> What these functions have in common is that they do something
> side-effectful, i.e. they do something over and above returning a
> value.


Well, yes, but they're also unsafe to run in an STM transaction, except
potentially for run!.

I think that's the convention followed by many in the
> community, although it's not a perfect convention -- there are many
> side-effecting functions in core without exclamation marks (print,
> require, ns-unmap).
>

require and ns-unmap are side-effecting, but idempotent, meaning that
they're safe to run in a transaction.

Functions that reference I/O like print or slurp are of course obviously
unsafe, and in those cases maybe an exclamation mark was considered
redundant.

But I guess the answer is that there's no fixed convention for ending a
function with an exclamation mark. The Clojure Style Guide suggests
exclamation marks should be for functions that are unsafe to use in STM
transactions, and I thought that stemmed from their usage in clojure.core,
but maybe the meaning is much looser than that.

- James

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Re: Why does "clojure.core/run!" end in an exclamation mark?

[Shantanu Kumar]

I'm curious about `clojure.core/run!` too, but my question is whether it is 
meant to be a `reduce` variant of `clojure.core/doseq` or it has some other 
purpose.

Shantanu

On Saturday, 24 December 2016 21:37:11 UTC+5:30, James Reeves wrote:
>
> My understanding is that the convention used in clojure.core is to put an 
> exclamation mark onto the end of any function unsafe to run in a 
> transaction.
>
> Does the reasoning differ for "run!" or is it assumed that the function 
> passed to "run!" will not usually be idempotent?
>
> - James
>

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Why does "clojure.core/run!" end in an exclamation mark?

[James Reeves]

My understanding is that the convention used in clojure.core is to put an
exclamation mark onto the end of any function unsafe to run in a
transaction.

Does the reasoning differ for "run!" or is it assumed that the function
passed to "run!" will not usually be idempotent?

- James

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