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[Caml-list] Managing a polymorphic environment
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Date: 2004-08-12 (15:06)
From: Jean-Baptiste Rouquier <jrouquiethearchiveshouldhaveafewantispamtricks@e...>
Subject: Re: [Caml-list] Managing a polymorphic environment
Quoting Diego Olivier Fernandez Pons <>:

> 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
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 


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


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