why is option.none not of type option.None?

[pbadenski]

const success: option.None = option.none;

doesn't compile and the error is:

TS2322: Type 'Option<never>' is not assignable to type 'None'.
  Type 'Some<never>' is not assignable to type 'None'.
    Types of property '_tag' are incompatible.
      Type '"Some"' is not assignable to type '"None"'

Is this by design? Just trying to wrap my brains around it....

[DenisFrezzato]

none and some are seen as data constructors for the data type Option<A>, so both returns a new Option<A>. The purpose of data constructors is to create a new value of their data type. This applies for any data type and their respective data constructors. You should never deal with the type of the data constructors, but with the data type.

[pbadenski]

Why are None and Some interfaces exported then?

[enricopolanski]

Seems like a good point, I checked most of the fp-ts codebase and I can't find places where they are imported.

[waynevanson]

const success: option.None = option.none; is one of two types: Some<A> and None.

You'll need to narrow the type via an assetion:
const success: option.None = option.none as option.None
or
const success = option.none as option.None