Re: [Caml-list] Infix function composition operator

[Stephan Tolksdorf <st@sigmasquared.net>]

On Wed, Nov 10, 2010 at 14:13 -0000, Jon Harrop wrote:
> However, I don't see it as a useful advantage in practice because parser combinators are so tedious during development (they require constant attention as types evolve): you want code generation like ocamlyacc or camlp4. OCaml is a very strong contender here, of course.

Could you maybe elaborate a bit on what you find tedious with regard to 
evolving types in the context of parser combinators?

In my parser code (using FParsec in F#) most types get inferred by the 
compiler and in the remaining instances the type annotations can hardly 
be called tedious. Actually, I find the types and the Visual Studio 
tooltips with the inferred types rather helpful for development.

- Stephan

>
> Cheers,
> Jon.
>
>> -----Original Message-----
>> From: mark@proof-technologies.com [mailto:mark@proof-technologies.com]
>> Sent: 10 November 2010 13:44
>> To: jonathandeanharrop@googlemail.com; yminsky@gmail.com;
>> arlen@noblesamurai.com
>> Cc: caml-list@inria.fr
>> Subject: Re: [Caml-list] Infix function composition operator
>>
>> So how does value restriction affect things here?  (excuse my lack of
>> knowledge)
>>
>> One thing about using a pipeline like this is that it relies on '|>'
>> being
>> left-associative (which it is due to OCaml's convention on operators
>> that
>> start with "|").
>>
>> Mark.
>>
>>
>> on 10/11/10 12:52 PM, Jon Harrop<jonathandeanharrop@googlemail.com>
>> wrote:
>>
>>> A pipeline operator is usually preferred over function composition in
>> impure
>>> languages like OCaml and F# due to the value restriction. For
>> example,
>> your
>>> example would be written in F# as:
>>>
>>> x |>  op1 |>  op2 |>  op3 |>  op4 |>  op5
>>>
>>> This style is very common in F#, particularly when dealing with
>> collections.
>>>
>>> Cheers,
>>> Jon.
>>>
>>>> -----Original Message-----
>>>> From: caml-list-bounces@yquem.inria.fr [mailto:caml-list-
>>>> bounces@yquem.inria.fr] On Behalf Of mark@proof-technologies.com
>>>> Sent: 10 November 2010 07:00
>>>> To: yminsky@gmail.com; arlen@noblesamurai.com
>>>> Cc: caml-list@inria.fr
>>>> Subject: Re: [Caml-list] Infix function composition operator
>>>>
>>>> on 10/11/10 3:45 AM, yminsky@gmail.com wrote:
>>>>
>>>>> This is probably a minority opinion, but I have written and read
>>>> quite a
>>>> lot
>>>>> of OCaml code over the years, and I've seen surprisingly few
>>>> effective
>>>> uses
>>>>> of the composition operator.  Somehow, I usually find that code
>> that
>>>> avoids
>>>>> it is simpler and easier to read.
>>>>
>>>> I agree that using a composition operator can make the code obtuse,
>> and
>>>> so
>>>> should not be overused.  But it's incredibly useful for certain
>>>> situations:
>>>>
>>>> 1) If you are performing a long chain of composed operations, it
>> avoids
>>>> nested bracketing piling up.
>>>>
>>>> For example:
>>>>        (op5<<- op4<<- op3<<- op2<<- op1) x
>>>> Instead of:
>>>>        op5 (op4 (op3 (op2 (op1 x))))
>>>>
>>>> This sort of thing happens quite a lot in certain applications, e.g.
>> in
>>>> language processing, to get at subexpressions.
>>>>
>>>> 2) Creating an anonymous function to be passed as an argument, it
>>>> avoids
>>>> explicitly mentioning arguments of that function.
>>>>
>>>> This sort of thing can happen a lot in functional programming
>>>> generally.
>>>>
>>>> For example:
>>>>        List.map (op2<<- op1) xs
>>>> Instead of:
>>>>        List.map (fun x ->  op2 (op1 x)) xs
>>>>
>>>> Mark Adams
>>>>
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>>>
>>>
>>>
>
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