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Re: How do I really do this?

From: Marco Parrone
Subject: Re: How do I really do this?
Date: Wed, 10 Mar 2004 01:29:54 +0100
User-agent: Gnus/5.1006 (Gnus v5.10.6) Emacs/21.3 (gnu/linux)

Bruce Korb on Wed, 03 Mar 2004 15:52:15 -0800 writes:

> I would like to be able to associate a value with a string.
> hash functions look perfect, except I can't use them unless
> I have a hash table and there isn't any clear way I've found
> to create hash table entries without having a hash table.

Why don't you create the empty hash-table first with `make-hash-table'?

Then you add entries using `hashq-set!' and alike, and you read values
using `hashq-ref' and alike.

guile> (make-hash-table 10)
#(() () () () () () () () () ())
guile> (define myhash (make-hash-table 10))
guile> (hashq-set! myhash 'myvarname "myvarvalue")
guile> myhash
#(() () () () ((myvarname . "myvarvalue")) () () () () ())
guile> (hashq-ref myhash 'myvarname)

> I've tried:
>   (define (string->symbol (function-returning-string))
>           (value-function))
> I thought that to be really obvious, but I was wrong.

Some ways are:

guile> (eval-string "(define abc 1)")
guile> abc
guile> (eval `(define ,(string->symbol "mytestvarname") ,1) 
guile> mytestvarname

> Meanwhile, can someone send me a hint?

Another way would be to use an associative list, a list of key and
value pairs, and get values using (cdr (assq KEY ASSOCLIST)).

guile> (define myassoc (list (cons 'key1 "val1") (cons 'key2 "val2")))
guile> myassoc
((key1 . "val1") (key2 . "val2"))
guile> (assq 'key1 myassoc)
(key1 . "val1")
guile> (cdr (assq 'key1 myassoc))

> If either of these mecanisms are documented somewhere,
> I'd gladly read it.

The guile info manual is great :)

Marco Parrone (marc0) <address@hidden> [0x45070AD6]

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