Subject: Re: writing/printing hash-tables to a file From: Erik Naggum <firstname.lastname@example.org> Date: 1998/06/28 Newsgroups: comp.lang.lisp Message-ID: <email@example.com> * kp gores | how do i "print" a hash-table to a file? sometimes, it works to print the hash-table object with *PRINT-READABLY* true. when that fails, you need to make a load-form for the object, and you might legitimately expect a system to contain something to help you with that. I found a function EXCL::MAKE-HASH-TABLE-LOAD-FORM in Allegro CL (for Unix) which appears to offer a reasonable efficiency gain: CL-USER(37): (let ((table (make-hash-table :test #'equal))) (setf (gethash "foo" table) "bar") (setf (gethash "bar" table) "zot") (excl::make-hash-table-load-form table nil)) (let ((hash-table (make-hash-table :test 'equal :size 103 :rehash-size 1.2 :rehash-threshold 0.6407767))) (excl::hash-table-fill hash-table #("bar" "zot" "foo" "bar"))) it appears that the other way to handle this, using the FASL read/write functions in Allegro CL (for Unix), actually produces the exact same function calls on loading as the above load-form. this probably shouldn't come as a surprise, but, anyway, here's how to write and read a hash table to a file with the simplest FASL read/write mechanism: CL-USER(47): (let ((table (make-hash-table :test #'equal))) (setf (gethash "foo" table) "bar") (setf (gethash "bar" table) "zot") (fasl-write table "/tmp/hash-table.fasl")) t CL-USER(48): (fasl-read "/tmp/hash-table.fasl") (#<equal hash-table with 2 entries @ #x2076ae82>) if you wish to write more objects to the same file, use FASL-OPEN to get a FASL stream and write to it, instead: CL-USER(53): (with-open-stream (fasl (fasl-open "/tmp/hash-table.fasl")) (let ((table (make-hash-table :test #'equal))) (setf (gethash "foo" table) "bar") (setf (gethash "bar" table) "zot") (fasl-write table fasl) (fasl-write table fasl))) t CL-USER(54): (fasl-read "/tmp/hash-table.fasl") (#<equal hash-table with 2 entries @ #x20799e2a> #<equal hash-table with 2 entries @ #x2079a4d2>) | i want to read the hash-table back from a file later, work with it, | add/delete entries and then save it back. this sounds more like you actually want a "hash table" to reside on disk and have a mapping onto a simple file-based database. or in other words, persistent objects. neither printable/loadable hash tables nor persistent objects are fully portable features in Common Lisp, i.e., you will need to use functions specific to the implementation in _some_ way. other Common Lisps offer other ways than Allegro CL, but the above is at least how I do it. #:Erik -- http://www.naggum.no/spam.html is about my spam protection scheme and how to guarantee that you reach me. in brief: if you reply to a news article of mine, be sure to include an In-Reply-To or References header with the message-ID of that message in it. otherwise, you need to read that page.