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Re: Somehow I have got this "thunk" thing wrong.
From: |
Christopher Baines |
Subject: |
Re: Somehow I have got this "thunk" thing wrong. |
Date: |
Sat, 06 Mar 2021 00:26:39 +0000 |
User-agent: |
mu4e 1.4.15; emacs 27.1 |
Tim Meehan <btmeehan@gmail.com> writes:
> I wanted to store a thunk in a hashtable so that I could look up its key
> and then run it later. Something like this:
>
> #! /usr/bin/guile
> !#
>
> (use-modules (ice-9 hash-table))
>
> (define stuff (alist->hash-table
> '((a . (lambda () (display "event a\n")))
> (b . (lambda () (display "event b\n")))
> (c . (lambda () (display "event c\n"))))))
>
> (define res (hash-ref stuff 'a))
> (res)
>
> But when I run it:
> Wrong type to apply: (lambda () (display "event a\n"))
The lambda bit you've written is quoted. So you're asking Guile to apply
a list where the first element is the symbol 'lambda, the second is the
empty list, ...
You probably want something like this, where you're creating a list of
pairs, where the car of the pair is a symbol, and the cdr is a procedure
(rather than a list).
(define stuff (alist->hash-table
`((a . ,(lambda () (display "event a\n")))
(b . ,(lambda () (display "event b\n")))
(c . ,(lambda () (display "event c\n"))))))
Does that make sense?
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