Function Composition

[Jed Wesley-Smith]

Well, I'm not arguing the merits of one or the other, indeed I'd like
both (and I usually use the andThen/; form). I'd just argue that this
is a well established name/form and there is value (as in least
surprise) in following the precedent.

Function<A, B> f = …
Function<B, C> g = …

Function<A, C> c = g.compose(f);
Function<A, C> d = f.andThen(g);

I'd argue the second form reads better anyway!

cheers,
jed.

On 2 January 2013 11:07, John Nilsson <john at milsson.nu> wrote:
> For what it's worth. I think the math people got it wrong with "∘". The
> other operation they call compose: ";" - which has applicative order - feels
> more natural. So one vote for keeping compose as ";". Also, this is the
> composition operation for statements Java programmers have been using for
> years with no complaint, so why arbitrarily switch to "∘" for function
> composition?
> Besides even the math people revert to applicative order when modelling
> function composition as a category.
>
> BR,
> John
>
>
> On Wed, Jan 2, 2013 at 12:40 AM, Jed Wesley-Smith <jed at wesleysmith.io>
> wrote:
>>
>> hello lambdarians!
>>
>> Just noticed that the java.util.function.Function.compose method is
>> round the wrong way (according to the common definition of function
>> composition*).
>>
>> The current lambda definition:
>>
>>
>> http://hg.openjdk.java.net/lambda/lambda/jdk/file/858e2f478d62/src/share/classes/java/util/function/Function.java
>>
>> has f.compose(g) mean apply f and then apply g, whereas the usual
>> (most other languages and the literature) has f ∘ g mean apply g and
>> then apply f.
>>
>> The form that Function has currently is commonly known as andThen. So,
>> you could rename the current method andThen and add a new compose
>> method that works in the usual manner.
>>
>> cheers,
>> jed.
>>
>> * references:
>> http://en.wikipedia.org/wiki/Function_composition
>> http://en.wikipedia.org/wiki/Function_composition_(computer_science)