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Functional unparsing
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Date: 2009-04-16 (09:25)
From: Cedric Auger <Cedric.Auger@l...>
Subject: Re: [Caml-list] Functional unparsing
Andrey Riabushenko a écrit :
> Hi ocaml developers,
> I am currently developing a library for multivariate regressions including 
> linear, nonlinear, generalized, weighted and so on. In my opinion most the 
> convenient interface is the one described further and is based on functional 
> unparsing.
> Something like that:
> Stats.linear_regression "y ~ x1 exp(x2) log(x3) x3^2" 
> Returns float -> float -> float -> float -> regression_result = <fun>
> Stats.generalized_regression "log(y) ~ x1 x^2 log(x3) " 
> Returns float -> float -> float -> float -> regression_result = <fun>
> For time series:
> Stats.ts_regression "y ~ ARMA(5,3)"
> Stats.ts_regression "y ~ ARMA(2,2) GARCH(2,1)"
> If want to ask you two questions. 
> 1. Do you find such interface convenient? Critique is welcome. If you have 
> better idea, please tell me. I will make all publicly available.
I don't know what is really itended, but  I think implementing something 
" let double x = 2 *. x in
  Stats.linear_regression "y ~ double x1""
  will be painfull, since you need to parse
  the string according to the environnement.

 The solution
 " let double x = 2 *. x in
  Stats.linear_regression "y ~ %1 x1" double"
closer to printf and format %1 meaning "float -> float" is easier to 
but less readable.

If you don't require custom function, what you think should do the trick 
and seems to be manageable, but maybe that will be awfull to repeat many 
times the same function in case of use in different places.
> 2. The second question regarding function unparsing. I haven't used this 
> technique before. Are there some docs, blog articles, descriptions and etc? 
> The only relevant documentation I have found is printf.ml :). Might someone 
> have a minimal working example to demonstrate?
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You can also take a look in format.ml, but it will be more complicate.
I don't know if it is a good idea, but if your expressions are 
complicate, try to use ocamllex and ocamlyacc.

Another thing, printf is simplistic in the syntax of the string, that is 
you only have text and no complicate expression to type (we can printf 
"x log () / 0"), but complicate in managing formatters you don't need 
(printf "it is %s o clock" time) with your examples (you have no 
parameter); from this point of view, ocamllex and ocamlyacc may be more 
relevant (and are well documented).

Cédric AUGER

Univ Paris-Sud, Laboratoire LRI, UMR 8623, F-91405, Orsay