What's the best way to chain updates?

[Rex van der Spuy]

Hi Everyone,

Usually when I want a series of updates to chain in sequence, I'll write some code like this:

FirstThing ->

  let 

    newModel = { model | -- update the record properties -- }

  in

    update SecondThing newModel

SecondThing ->

  let 

    newModel = { model | -- update the record properties -- }

  in

    update ThirdThing newModel

ThirdThing ->

  let 

    newModel = { model | -- update the record properties -- }

  in

    update LastThing newModel

LastThing ->

  let 

    newModel = { model | -- update the record properties -- }

  in

    newModel ! [ ]

But... isn't this similar to using a GOTO statement in BASIC?

(Hey, I love BASIC, but... !)

I've found that when I have a few of these chained in sequence, spaghetti code is the guaranteed result.

Is there someway to manage this sequencing in some kind of centralized way?

For example, something like:

SequenceOfSteps ->

  FirstThing 

  SecondThing

  ThirdThing

  LastThing

It would be nice to do this so that I can selectively insert or remove steps while testing my application.

Is this possible?

Any advice or opinions?

[Simon]

I think you want to do something like:

 { model | -- update the record properties -- }
|> update SecondThing 
|> update ThirdThing 
|> update FourthThing

[Rex van der Spuy]

Oh, now it seems obvious! :)

Thanks so much!

[Desmond D'Souza]

There is a more detailed explanation here and here and here.