So a realistic example:

purchaseCardContents

calls

purchaseCardContents

which calls

toPurchaseCardContent

several times. Now I need a class

FormatSavings

in the last function

toPurchaseCardContent

. How do I get it there? When using a class for the whole logic, I just inject it through the constructor. The issue here is that

toPurchaseCardContent

doesn't know anything about

purchaseCardContents

so I would need to pass-through that class and everything else it needs. Maybe the better question is: How do I get / pass dependencies I don't want the caller to bother about in functional programming?

This code seems to have a quite narrow scope, I don't see how you could make something generic or apply some pattern I know (I don't know all of them though, far from this)