I find this post about “Sum type” (union type) to be very helpful!
https://medium.com/@willkurt/why-sum-types-matter-in-haskell-ba2c1ab4e372#.vg3fb2ozc
he9lin
Qqwy
TypeCheck Core Team
Nice!
Structs are product types. I wonder in what way we could simulate Sum types in Elixir. What I can think of so far is to ‘emulate’ them by having a struct where one of the keys is only ever one of a small subset of allowed atoms.
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jswny
In regards to the Maybe type, I am not amazingly well-versed in functional programming or Elixir but I was under the impression that these were unnecessary in Elixir because of function return values like :error and {:ok, value}. Does anyone know of any use cases in which these conventions would be inferior to a Maybe type (or Option type)?
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Qqwy
TypeCheck Core Team
@jswny {:ok, value} | :error, als known as the ok-Tuple or Success Tuple, is exactly a Maybe type.
However, because it is a special kind of tuple, and not a struct, it is not possible to use it in protocol dispatching. Furthermore, (and in part because of that,) Elixir is missing many of the nice functions/functionality that could be written for the Maybe type.
This is exactly what FunLand provides: (Besides other behaviours and implementations) it provides the possibility to map functions over the Success Tuple, combine the results of two Success Tuples, put arbitrary values inside a new Success Tuple, etc.
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OvermindDL1
Which I still find odd. Protocols just compile to multiple function heads yes? That means it should be trivial to match on structure…
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