F# recursive function arguments and stack overflow

Question

I am somewhat new to F#, and I came across some strange behaviour when I was working with some recursive functions. I have two different versions of it below:

Version 1:
This causes a stack overflow, though it seems that it shouldn't (at least to my noob eyes)

let rec iMake acc =
  match acc with
  | 10 -> 100
  | _ -> iMake acc+1

Version2:
This one works as I would expect it to.

let rec iMake acc =
  match acc with
  | 10 -> 100
  | _ -> iMake (acc+1)

The only difference is that version 2 puts the acc+1 expression into parenthesis. So my question is, why does the first version not work, but the second one does? Does this mean that I should put all of my function arguments into parenthesis to avoid this type of stuff in the future ?

Eugene Fotin · Accepted Answer · 2014-02-07 13:52:07Z

3

Function call has higher precedence than binary operator +. So the first function actually works like:

let rec iMake acc =
    match acc with
    | 10 -> 100
    | _ -> (iMake acc)+1

answered Feb 7, 2014 at 13:52

Eugene Fotin

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1 Comment

A.R. Over a year ago

I see, so it is trying to add one to the result of (iMake acc), and that is where the stackoverflow is coming from. acc is effectively never incremeted, interesting.

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