Re: [Caml-list] Managing a polymorphic environment

[Jean-Baptiste Rouquier <jrouquiethearchiveshouldhaveafewantispamtricks@ens-lyon.fr>]

Quoting Diego Olivier Fernandez Pons <Diego.FERNANDEZ_PONS@etu.upmc.fr>:

> let x = ...
> Env.add x "the number of elements in the knapsack"
> let c = ...
> Env.add c "the total cost of the knapsack"
> 
> 
> The idea is of course to be able to pretty-print the result
> 
> # Env.print_int x;;
> the number of elements in the knapsack is 10 - : unit = ()
> # Env.print_float c
> the total cost of the knapsack is 100.0 - : unit = ()

I'm finishing a lib to handle configuration files, which meets the same kind of
problem : one would like pretty print (and read back) the values, but handle
them in type safe way inside the programme.
I'm using objects and I think it can solve your problem : have a class Env.foo
that has a virtual method print (and any other method to implement the functions
you want in Env), and have classes foo_int and foo_float that inherit from it.
Then your code will be written

let x = new foo_int 10 "the number of elements in the knapsack"
Env.add x (*x is coerced to foo, we forget it's an int*)
let c = new foo_float "the total cost of the knapsack"
Env.add c 

x#print
c#print


I can send you my code if you want more details.

Jean-Baptiste.
http://perso.ens-lyon.fr/jean-baptiste.rouquier

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