Handling Type Errors in Safe Data Transformation with TypeScript

I have a type error that's probably due to me doing something wrong.
I'm trying to do some safe data transformation. At the first line I've validated that

query.results.rows

query.results.rows

is an

Array<Schema.Unknown>

Array<Schema.Unknown>

and I expect it to have a single item at this point, but I don't know so I wrap it in an Option, then I want to to decode it to a particular row type, so I do a match on the option and, if it's some it becomes the

Either

Either

returned by the

Schema.decode

Schema.decode

call, or if none, I turn it into an

Either.left

Either.left

.
The problem with this is that the type of the value becomes:

Either.Either<never, string> | Either.Either<{...}, ParseError>

Either.Either<never, string> | Either.Either<{...}, ParseError>

so the type is the union of my branch types, and then when I map over it the value becomes

never | {...}

never | {...}

and typescript complins.
I guess my broader question is how do I pipe these sort of data transformations and collect the

left

left

side, because my first attempt when I tried to use

map

map

most of the time resulted in me having nested Either or an Either nested in an Option which doesn't feel great. I hope this makes sense

Effect Community•2y ago

boqdan

Handling Type Errors in Safe Data Transformation with TypeScript

I have a type error that's probably due to me doing something wrong.
I'm trying to do some safe data transformation. At the first line I've validated that

query.results.rows

query.results.rows

is an

Array<Schema.Unknown>

Array<Schema.Unknown>

Either

Either

returned by the

Schema.decode

Schema.decode

call, or if none, I turn it into an

Either.left

Either.left

.
The problem with this is that the type of the value becomes:

Either.Either<never, string> | Either.Either<{...}, ParseError>

Either.Either<never, string> | Either.Either<{...}, ParseError>

so the type is the union of my branch types, and then when I map over it the value becomes

never | {...}

never | {...}

and typescript complins.
I guess my broader question is how do I pipe these sort of data transformations and collect the

left

left

side, because my first attempt when I tried to use

map

map

most of the time resulted in me having nested Either or an Either nested in an Option which doesn't feel great. I hope this makes sense

Handling Type Errors in Safe Data Transformation with TypeScript

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