Guide to transforming a TaskOption into a TaskEither with fp-ts

I have a method that can locate an item in the database and retrieve a TaskOption:

find: (key: SchemaInfo) => TO.TaskOption<Schema>

and another method to store it:

register: (schema: Schema) => TE.TaskEither<Error, void>

Within my register function, I want to verify if the Schema being saved already exists or not (using find), but I'm unsure how to convert a TaskOption to a TaskEither. My attempt was:

pipe(
    findSchema(schema.info),
    TE.fromTaskOption,
    TE.swap
)

However, the result from TE.fromTaskOption is not the expected TaskEither. I also tried TE.fromTaskOptionK, but it returned a strange function instead.

In my scenario, if the TaskOption is none, I proceed with saving (indicating the schema is not yet registered); otherwise, I return an error (as the schema is already registered). How can I resolve this issue?

typescriptfunctional-programmingfp-ts

Answer №1

When you use TE.fromTaskOption with a None value, make sure to put the value into Left

Consider this approach:

pipe(
    findSchema(schema.info),
    TE.fromTaskOption(() => "No schema"),
    TE.swap
)

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