CODEWITHSUNDEEP
f#
Sal-laS
Sal-laS

Reputation: 11649

Where is the parameter defined

This is a simple implimentation of factorial function in F#

let rec fact =function
   | 0->1
   | n-> n * fact(n-1);;



   fact 5

1- what is the role of the rec word here?

2- fact is the function, but it is never mentioned that it can have a parameter. So technically it should face with an error, since in the signature (let rec fact ) there is no parameter defined for it. So how does it works?

Upvotes: 2

Views: 84

Answers (1)

MarcinJuraszek
MarcinJuraszek

Reputation: 125650

1) rec is used to mark function as recursive. Without it you would not be able to call it from within the function implementation. Read more on MSDN: Recursive Functions: The rec Keyword (F#)

2) let rec fact = function is a shortcut for:

let rec fact argument =
   match argument with
   | 0 -> 1
   | n -> n * fact (n-1)

As you can see, there is a single parameter which is pattern matched with provided conditions.

It's called a pattern matching function and is described on MSDN: Match Expressions (F#)

Upvotes: 6

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