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Is |> a special case?
f#book

I'm working through Expert F# and on p 45, there's a sidebar that talks about the definition of the |> forward pipe operator. It breaks it down as:

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let (|>) x f = f x

Unless I misunderstand part of that definition, it looks like a normal function declaration except it uses special characters "|>" instead of a name like "test".

As far as I understand so far, |> does not act like a normal function. A normal function declaration would require |> to be listed before all of it's arguments in an expression, but instead it can be used sorta like an infix operator.

I guess what I'm trying to figure out is whether the definition in the book is an over simplification or does the operator act more like a special case?

James

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Hi James,

It's not a special case, F# allows you to define custom prefix and in-fix operators - this is just a custom operator infix operator.

Cheers,
Rob

By on 2/12/2008 1:45 PM ()

Thanks for quick response.

I tried it out and created an operator that behaved just like the |>, but called +>. Okay that makes some sense. The definition was as simple as the book suggested. Puts my mind at ease.

I am assuming, then, the syntax shown there can only be used with operator characters. For example, if I try:

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2
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let (test) f x = x f
I get a syntax error.
let test f x = x f

does not cause a syntax error, but cannot be used as an infix notation.

Am I on track?

By on 2/12/2008 2:23 PM ()

Yes, only operator characters can be operators and the first character determines whether it is post fix or infix. The informal specifications has the full details:
[link:research.microsoft.com]

Cheers,
Rob

By on 2/13/2008 12:00 AM ()

Thanks, again!

By on 2/13/2008 4:07 PM ()

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