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Adventures in F# Part 1.5

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Telastyn

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Holy crap, a comment!

In other news, I dabbled a little more with F# over the past days. The BigInt stuff seems to be missing a lot, and the intellisense on stuff seems wonky. For list/List at least, it tends to oscillate between three visible types; only one really containing the useful (if sometimes terribly named) bits.

I found a few more pattern matching examples ( (n::_) for something starting a list for example) which make it a little niftier than sugar for if/else blocks. Still a disappointment. The style does though lend itself very, very nicely towards algorithm implementation. I got half through an implementation of the quadratic sieve before I realized that BigInt kinda sucked.

So I went on to a traditional interview question that I've always seemed to have trouble with: "Reverse a string in place."


let rec reverse a =
match a with
| [] -> []
| _ -> (reverse (List.tl a)) @ [List.hd a]







Still fairly newbish with the language, but it took 1 shot and about a minute. No BS pointer arithmetic; straight-forward and easy to remember. Now if only this tl/hd/car/cdr bull could go the way of "let's see how much we can do in one line of code!" perl.

God I hate that stuff.
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your code with more sugar and done with safer matching

let rec rev a  =

match a with
| [] -> a
| x::xs -> rev xs @ [x]


then u can '_ -> failwith "?"'.

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Okay, but doesn't the usage of List.hd, etc cause the parameter of the function be a List via inference? There would be a compile-time error if not a list is passed rather than using x::xs/_ -> fail which would be runtime? I will double check tonight.

[edit: The cons style does the same effect, only via matching. Points for Daerax]

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