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[Caml-list] Easy solution in OCaml?
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Date: 2003-04-27 (16:12)
From: Siegfried Gonzi <siegfried.gonzi@s...>
Subject: Re: [Caml-list] Easy solution in OCaml?
>Brian Hurt wrote:
>If you don't know what you just pulled out of a list, how can you do 
>anything with it?  About all you can do with it is to move it around.  
>Take it out of one data structure and put it into another.  Or pass it to 
>some other function.  Which you can quite happily do with Ocaml- take a 
>look at or Array.of_list in the standard libraries for examples.
>But once you want to do something more with the elements than just move 
>them around, you need to know what they are- what type they are.  So let's 
>say I'm expecting that I'm dealing with an int list list (your first 
>example there).  I could easily convert this to a float list list by 
>let conv lst = (fun l -> (float_of_int) l) lst
>With some suitable generic handling, instead of calling, I just 
>call map, so when I hit an array of ints instead of a list of ints, I call 
> and not  It could be done, it'd be of limited use but 
>it could be done.  But what am I supposed to do with the string "hi guy"?  
>Should it treat the string as a list of char, implicitly convert it to a 
>list of int, and then convert the list of int to a list of float, 
>returning [104.; 105.; 32.; 103.; 117.; 121.]?  What sensible thing can 
>you do here?
>This is what I meant about a bug in your program or not thinking the 
>design through.  If there is a reason you're putting a string into that 
>list, it means something.  Decide what it means, and at each point you 
>handle elements from that list, decide what to do if you see a string- 
>even if it's just "ignore it and go on", think about it and decide.

Before I commence I have to say: there exists actually only 2 functional 
languages which  deserve to be used by industry: this is OCaml and 
Haskell. Okay, in the Scheme realm only Bigloo (and mybe PLT Scheme) 
stands for "ready for industry".  But I have to say that Clean's elegant 
syntax is way, way, way above OCaml ones.

It is often very comfortable to use this sort of bad hacking, because in 
science when you develop new functions or tries to solve problems you 
often do not know in advance what you want and not.

For example: function1 has as return: erg1 = (list (list 2 3 4))

function2 expects output from function1  and function2 uses this output 
as follows:

(list-ref  erg1 0)

But now I decide for reason of its own that erg1 should include just one 
more information:

erg1 = (list1 (list 2 3 4)  (list (vector 2 3 4) "nice day"))

function2 now is not affected because it always uses the first element 
of the list, but it dramatically shortens your development time, because 
you do not have to cope with other structures or tuples in erg1 as you 
would do lets say in Clean. And you do not have to change  all your 
other dependencies.

This was the reason to ask in my first post of the topic are there any 
guys out there who successfully use OCaml for data evaluation or lets 
call it statistic (which means reading files, coping with array and 
lists and that sort of). Maybe the aforementioned bad feature of 
Scheme/Lisp/Python... makes them that usefull for coping with "dynamic" 

This also  leads to the question: is development time really reduced in 
(strict typed) functional programming, or is it only reduced when you 
compare quicksort in Haskell and the verbose version in C.

S. Gonzi

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