Lisp -- Getting Started

I took a deep breath when starting this blog post. Lisp is such an arcane programming language. I am not sure I will benefit from it at all. However, since pgloader is written in CL, I think I should have a try.

Most of the following is about Common Lisp.

SBCL

ASDF

Quicklisp

Reader Macros

Reader Macros is kind of similar to macros in C. This blog post shows how to use it to modify the CL parser to parse json. Often in a CL project, you will see code such as #+sbcl or #+ccl, which is used to conditionally include/exclude code based on whether sbcl or ccl is used. The counterparty in C is #ifdef xxx or if constexpr in C++.

As a beginner, I was quite confused by the usage of special characters such as #\, #:, +name+, *name* etc. Most of them are reader macros! Common Lips calls them “dispatching macro character” more specifically. In Common Lisp, a dispatching macro character is a type of macro character that dispatches to another function based on the character that follows it.

Sharp (#) is the mostly frequently used dispatching macro. CLHS has a chapter for it: link. Some common ones are list below.

1. #\: character literal. For example, #\Backspace denotes a backspace, and #\' denotes a single quote.
2. #(: simple vector. For example: #(a b c )
3. #:: uninterned symbol.
4. #+: read-time conditionalization facility.

Some of these special character are not reader macros, but pure styling convention. See Common Lips style guide:

• Constants should be surrounded with plus signs
• Special variables (Mutable globals) should be surrounded by asterisks.