>
> We have found that this pattern is typically a good case for chaining a
> bunch of andThen statements with a withDefault statement at the end
> together. The one thing is you would have to be able to adjust your values
> to all be Maybes.
>
Yes Christian, I am wondering if people are aware of some more generic
continuation pattern matching syntax. The andThen expression is very useful
for monadic types like Maybe. (sorry for the M term use ^^ but it seemed
appropiate even if I'm not into category theory). But in my exemples, I'm
using Union types that are not Maybes. I guess what I could do is create my
own "andThenX" like this:
f1 : Var1 -> Type2
f2 : Var2 -> Type3
...
Type Type2
= DataType2 Var2
| ...
Type Type3
= DataType3 Var3
| ...
andThen2 : (Var2 -> a) -> Type2 -> Maybe a
andThen2 f2 type2 =
case type2 of
DataType2 var2 ->
Just (f2 var2)
_ ->
Nothing
andThen3 : (Var3 -> a) -> Type3 -> Maybe a
andThen3 f3 type3 =
case type3 of
DataType3 var3 ->
Just (f3 var3)
_ ->
Nothing
...
And then (no pun intended ^^) do something like:
f1 var1
|> andThen2 f2
|> andThen (andThen3 f3)
|> ...
|> andThen (andThenN fN)
|> withDefault otherwise
This has the advantage of having a clear flow, but the inconvenient that I
need to write the my special andThenX functions.
What do you think of this approach?
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