How to extract data from Result type

[suraj-mandal]

How can I extract data from the Result datatype. I mean for example:

import gleam/list.{last}
last_pascal_output = [[1], [1, 1]]
let last_row: Result(List(Int), Nil) = last(last_pascal_output)

This should return

Ok([1, 1])

Here how to extract [1, 1] from this?

[lpil]

Hello! There's a few different ways to do it.

The main way is to not extract the value, but instead to push the rest of the computation into the result. The result module is useful for this with it's functions map, then, etc.

[[1], [1, 1]]
|> list.last
|> result.map(fn(x) {
  // do something with x here...
})

This can also be written with use

use x <- result.map(list.last([[1], [1, 1]]))
// do something with x here...

Another way is to use result.unwrap or a case expression to extract the value out and use a default value if it is an Error.

Lastly you can use assert Ok(x) = list.last(my_list). This is convenient but great care must be used as it will cause the program to crash if the pattern does not match.

[suraj-mandal]

Thanks a lot for your useful insights!