alphapapa

Reader Macros in Common Lisp

This post also appears on lisper.in.

Reader macros are perhaps not as famous as ordinary macros. While macros are a great way to create your own DSL, reader macros provide even greater flexibility by allowing you to create entirely new syntax on top of Lisp.

Paul Graham explains them very well in [On Lisp][] (Chapter 17, Read-Macros):

The three big moments in a Lisp expression's life are read-time, compile-time, and runtime. Functions are in control at runtime. Macros give us a chance to perform transformations on programs at compile-time. ...read-macros... do their work at read-time.

alphapapa

#!/usr/bin/perl
#
# Brad's el-ghetto do-our-storage-stacks-lie?-script
#

sub usage {
    die <<'END';
Usage: diskchecker.pl -s <server[:port]> verify <file>
       diskchecker.pl -s <server[:port]> create <file> <size_in_MB>
       diskchecker.pl -l [port]

alphapapa

(defun my-filter-current-buffer (program &rest args)
  (let* ((stdout-buffer (generate-new-buffer " stdout"))
         (ret (apply 'call-process-region (point-min) (point-max) program
                     nil (list stdout-buffer) nil args)))
    (when (zerop ret)
      (let ((output (with-current-buffer stdout-buffer
                      (buffer-string))))
        (erase-buffer)
        (insert output)))
    (kill-buffer stdout-buffer)))

alphapapa

// createshortcut.js -- ++pentadactyl
// @Author:      eric.zou (frederick.zou@gmail.com)
// @License:     GPL (see http://www.gnu.org/licenses/gpl.txt)
// @Created:     Tue 29 Nov 2011 01:24:05 PM CST
// @Last Change: Tue 29 Nov 2011 02:23:36 PM CST
// @Revision:    41
// @Description:
// @Usage:
// @TODO:
// @CHANGES:

alphapapa

Comments? sacha@sachachua.com

• Emacs learning curve?

Meta information

Assumptions

• Mix of Emacs geeks skewed towards people who’ve been using this for a while (after all, takes a certain commitment to come all the way to an Emacs conference!)

Outcomes

alphapapa

#!/usr/bin/env zsh
# -*- coding: UTF8 -*-

# Author: Guillaume Bouvier -- guillaume.bouvier@ens-cachan.org
# 2016-05-10 15:36:06 (UTC+0200)

format_duration()
{
    diff=$1 # Duration in seconds
    if test $diff -ge 86400; then

alphapapa

Relations

Relations are maintained through the outline hierarchy and special properties on the entries so we can model arbitrary graphs instead of only DAGs. This means you can define parents or children completely outside the hierarchy or even in different files.

Relations are kept in sync bidirectionally so please only use the API to maintain them otherwise things might get lost. Because the relations are bidirectional the graph traversal and querying is extremly fast.

Parents

Parents are defined by the GRAPH_PARENTS property as list of IDs and implicitly through the org outline hierarchy: all headlines above this one are this entry's parents.

alphapapa

;;; Neat convenience function for working with Elisp's EIEIO objects
(defmacro oref* (object &rest slots)
  "Like `oref', but each slot in SLOTS is applied in sequence.

For example,

  \(oref* obj :inner :property)

is equivalent to

alphapapa

;;; pp-debug.el --- Pretty-print debug frames  -*- lexical-binding: t -*-

;; Copyright (C) 2017 Felipe Ochoa

;; Author: Felipe Ochoa
;; Created: 5 Dec 2017
;; License: GPL

;;; Commentary:
;;; Pretty-print debugger frames.

alphapapa

*.enex