From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Olivier Dion via General Guile related discussions Newsgroups: gmane.lisp.guile.user Subject: Re: Somehow I have got this "thunk" thing wrong. Date: Fri, 05 Mar 2021 19:31:14 -0500 Message-ID: <87lfb1yvfx.fsf@clara> References: Reply-To: Olivier Dion Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="15621"; mail-complaints-to="usenet@ciao.gmane.io" To: Tim Meehan , guile-user Original-X-From: guile-user-bounces+guile-user=m.gmane-mx.org@gnu.org Sat Mar 06 01:30:26 2021 Return-path: Envelope-to: guile-user@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1lIKpt-0003xF-TK for guile-user@m.gmane-mx.org; Sat, 06 Mar 2021 01:30:25 +0100 Original-Received: from localhost ([::1]:49398 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lIKps-0001nX-S8 for guile-user@m.gmane-mx.org; Fri, 05 Mar 2021 19:30:24 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]:41664) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lIKpc-0001nP-5s for guile-user@gnu.org; Fri, 05 Mar 2021 19:30:08 -0500 Original-Received: from smtp.polymtl.ca ([132.207.4.11]:41573) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lIKpa-0004E4-53 for guile-user@gnu.org; Fri, 05 Mar 2021 19:30:07 -0500 Original-Received: from localhost ([89.36.78.234]) by smtp.polymtl.ca (8.14.7/8.14.7) with ESMTP id 1260TsTi029359 (version=TLSv1/SSLv3 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 5 Mar 2021 19:29:58 -0500 DKIM-Filter: OpenDKIM Filter v2.11.0 smtp.polymtl.ca 1260TsTi029359 In-Reply-To: X-Poly-FromMTA: ([89.36.78.234]) at Sat, 6 Mar 2021 00:29:54 +0000 Received-SPF: pass client-ip=132.207.4.11; envelope-from=olivier.dion@polymtl.ca; helo=smtp.polymtl.ca X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: guile-user@gnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: General Guile related discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: guile-user-bounces+guile-user=m.gmane-mx.org@gnu.org Original-Sender: "guile-user" Xref: news.gmane.io gmane.lisp.guile.user:17338 Archived-At: On Fri, 05 Mar 2021, Tim Meehan wrote: > 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")))))) You've quoted the whole s-exp. Which means lambda is never applied. You have to apply lambda in order to create a procedure. > > (define res (hash-ref stuff 'a)) > (res) > > But when I run it: > Wrong type to apply: (lambda () (display "event a\n")) You're trying to apply a list and not a procedure. This is because of the quote mentioned above. In other words, you're doing this: ---------------------------------------------------------------------- (apply '(lambda () (display "event a\n"))) ---------------------------------------------------------------------- Change the ' for ` and unquote the lambdas with ,. Like this: ---------------------------------------------------------------------- (define stuff (alist->hash-table `((a . ,(lambda () (display "event a\n"))) (b . ,(lambda () (display "event b\n"))) (c . ,(lambda () (display "event c\n")))))) ---------------------------------------------------------------------- Or use the list procedure instead of quoting: ---------------------------------------------------------------------- #! /usr/bin/guile !# (use-modules (ice-9 hash-table)) (define stuff (alist->hash-table (list (cons 'a (lambda () (display "event a\n"))) (cons 'b (lambda () (display "event b\n"))) (cons 'c (lambda () (display "event c\n")))))) (define res (hash-ref stuff 'a)) (res) ---------------------------------------------------------------------- -- Olivier Dion PolyMtl