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Basic Let question
f#book

I was reading 'Expert F#' by DonSyme book and when exprimenting one of the sameple code and I ran into a problem need help to
procede. The code I am talking about is on 11, it is mentioned that with the use
#light will take care of alignment and use of 'in'. But using fsi
1.4.9.19 when I start typing in the code, the code liiks like the
following 

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let poweroffourplus2 n = 
    let n = n * n 
    let n = n* n

When I entered the second line the fsi failed. I changed it and included 'in' in seond let to make sure may be it is because of #light still failed. I am bit confused. Could someone help me on this?

Thanks

.
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let poweroffourplus2 n = 
  let n = n * n 
  let n = n* n

The #light syntax is very similar to Python in that whitespace is significant. Therefore, the code must be indented - using spaces not tabs - to show code relationships. The function also needs to return a value in order to be valid. Finally, when using FSI the last line needs a double semcolon ";;" to end input:

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let poweroffourplus2 n =
    let n = n * n
    let n = n* n
    n;;
By on 7/31/2008 8:30 AM ()

Thank you very much and yes Don also mentioned the same in the same paragraph and I was eager to try to code without reading all the meat. I have one another question, this is realted to funcation thinking what exactly happening to n in the above example

when I use the first let (on the funcation definition) it is coming in as argument value. In the second let, the value of n is pass and creats a new n value (even though Don did mentioned the value of n doesn't change) here it is changing... now the next let uses n, it is using modified n instead of original n........

so how the value 'n' is not changed.??

Thanks again.

By on 7/31/2008 9:13 AM ()

This is 'shadowing' - each new 'let n = ...' creates a new variable which hides the old one. So

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let n = n * n
let n = n * n

is like

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let n_2 = n_1 * n_1
let n_3 = n_2 * n_2

only they all have the same name. None of the objects referred to by the name n_i is being mutated. Instead there are three different objects, and at different points in the code, the name 'n' refers to different ones of those objects.

By on 7/31/2008 3:07 PM ()

Thank you very much. I have one more question, I realised if I don't understand this correctly I am going to assume too many things so here is one more

in the following example

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let nbynplus5 n =
     let n = n * n
     let n = n + 5
     n;;

In the above example, the let n = n * n will be let n_1 = n * n since it is the first time n is referenced and in the second let, it will be let n_2 = n_1 + 5. Is this correct so if I have make the code it would be

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let nbynplus5 n =
     let n_1 = n * n
     let n_2 = n_1 + 5
     n_2;;

Is this correct? also why would be doing instead of using this modified code itself? Is it a style or coding standard?

Thanks again for helping me started.

By on 8/1/2008 7:53 AM ()

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