Indentation change after if-else expression not taken into account?

Question

Given this this operator for evaluation of side effects in pipelines

let inline (|>!) a f = f a ; a 

and this code snippet

Answer 1

This is not a bug, and it doesn't happen specifically for operators longer than two characters. This is a funny consequence of F#'s permissive offset rules.

When aligning lines of the same nestedness level, they have to be at the same indentation, like this:

let foo =
     bar
     baz
     qux

But this is not allowed:

let foo =
     bar
      baz  // Indented too much to the left
     qux

And neither is this:

let foo =
     bar
    baz  // Indented too little
     qux

When dealing with constructs that create nested blocks, such as if/then, this rule is used to determine when the block is over: it's when the indentation alignment is broken.

let x =
     if 1 = 1 then
       bar
       baz
     qux

But there is an exception to this rule: if the line starts with an operator, then it is allowed to be shifted to the left by at most the operator size plus 1 characters, and it will still be considered to be at "current" indentation.

For example, this works:

let x =
       1
     + 2
     + 3

But when you have operators of different sizes, it gets tricky. This works:

let x =
       1
     + 2
     + 3
    <> 6

But this doesn't:

let x =
        1
     +  2
     +  3
     <> 6