Question

I am trying to write a list comprehension in F# and can’t get it to compile:

[for x in xs do
    let y = f(x)
    when g(y) -> y]

Is there any way to save an intermediate computation in the middle of a list comprehension? How can I rework this list comprehension so that it compiles?

Answer 1

I would just skip the list comprehension.

let ys = xs |> List.map f |> List.filter g

However it is simple enough to get your code working.

let ys = [ for x in xs do
               let y = f(x)
               if g(y) then yield y ]