On Monday, October 2, 2017 at 11:04:52 PM UTC+2, Didier wrote:
>
> > Even in an impure language such as Common Lisp we frown on such LET forms
>
> True, but as far as I know, in Common Lisp, the condition handler is
> always in scope of where the error happened, so I wouldn't face this
> problem.
>
> I also struggle to split this up into functions without making it even
> more complicated. I'm intrigued by the interceptor pattern mentioned, I'll
> have to try it out, I worry its overkill, but not sure.
>
> My opposition to turning this into a chain, is that it complects the order
> of things, with the work of each step. My steps are pure functions, they
> take inputs and return outputs. They don't know anything about the full
> workflow, just their transformation. My orchestrating function is the one
> which knows how to compose the smaller pure steps, so that it can fulfill
> the business process.
>
No, your functions are not pure. Besides returning a value they can throw
an exception, i.e. they have a side-effect!
As we know from Haskell, this forces them to be evaluated in a sequential
order ... just ask yourself what value the variable c should be bound to if
an exception is thrown by doB.
Both suggested solutions seem to be reasonable. While try-let ignores all
bindings when an error occurs (check with macroexpand), the interceptor
chain probably can see all bindings established before the error occured (I
have not tested this though) and thus correctly imposes a sequential order.
Best,
Nils
The interceptor chain seems to still complect this a little. At least it
> has the steps know about each other since it relies on a common context,
> and expects previous steps to properly assoc the data needed by later steps.
>
>
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