Hi, what is the “nicest” way to partially apply more than a few parameters?

# arrow

[dnowak]

Hi, what is the “nicest” way to partially apply more than a few parameters?

[dnowak]

I know about two options:

val renderSmsTemplate: RenderSmsTemplate = ::renderTemplate.curried()(
        generateCommandId
)(
        generateMessageId
)(
        getNow
)(
        TopicName(TEMPLATE_COMMANDS_TOPIC)
)(
        TemplateId(templateId)
)

val sendSms: SendSms = ::sendSms
        .partially1(generateCommandId)
        .partially1(generateMessageId)
        .partially1(getNow)
        .partially1(TopicName(SMS_COMMANDS_TOPIC))

[dnowak]

Generally each function has the first parameters that are dependencies and the rest are actual parameters that are defined by some interface/type alias.

[dnowak]

What I’m looking for is to apply a few leading parameters. Ideally:

::sendSms.partially(generateCommandId, generateMessageId, getNow, TopicName(xx))

[Peter]

that’s the most interesting brackets i’ve seen in a long time 😅

[dnowak]

I have not found any other way to break the line 🙂

[HieiJ]

Hi, In the past I evaluated also the syntax

(::sendSms)(generateCommandId, generateMessageId, getNow, TopicName(xx))

but maybe the most idiomatic way to do it in kotlin (one that every kotlin dev can understand immediately) is just

{ sendSms(generateCommandId, generateMessageId, getNow, TopicName(xx)), it) }

[HieiJ]

or better

{ templateId -> sendSms(generateCommandId, generateMessageId, getNow, TopicName(xx)), templateId) }

[Youssef Shoaib [MOD]]

The issue is that you might have 5 other different parameters after that, or even worse you're gonna need to specify type parameters for them all.

[Youssef Shoaib [MOD]]

I think just like how curried is defined we can also define a partial-application invoke that returns ethe appropriate function, but this'll potentially need a huge amount of definitions

[Patrick Louis]

If you already have the curried version of the function, you could write a generalized uncurry4 function to partially apply the first 4 parameters in a single call.

fun <A,B,C,D,R> ((A)->(B)->(C)->(D)->R).uncurry4(): (A,B,C,D)->R = 
{ a: A, b:B, c:C, d:D -> 
    this(a)(b)(c)(d) 
}

[dnowak]

I was thinking about adding overloaded partially function that would apply n first arguments for all arities (1 - 22). But that means 253 * 2 functions (regular & suspend). I’m not sure if IDEA would be happy with that 🙂.

[dnowak]

It’s sad that partial application is not supported by Kotlin.