chaitanyagupta

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.

tune

Windows/Linuxで両方で動作する成果物を想定。 有償のツールは理解が得られる方が稀なので除外。

仕様書

外部仕様

Word/Excelが手軽だけど差分が追いにくい。 Markdown+PandocかSphinxでPDF提出がいいかな?

tune

#!/usr/bin/ruby

require "optparse"

mode = :help

opt = OptionParser.new
opt.on("-a", "Add BOM"){|v| mode = :add}
opt.on("-d", "Delete BOM"){|v| mode = :delete}
opt.parse!(ARGV)