ql-goheecus

CL-2DSYNTAX

The cl-2dsyntax is an indentation-sensitive reader system. Published in the public domain. Because lispers read the code by indentation and not by parentheses, I’ve decided to write a reader macro which removes the need for parentheses.

Download

The asdf-installable package: cl-2dsyntax.tar.gz

Usage

Activate the syntax by evaluating (cl-2dsyntax:enable-syntax), the reader macro is hooked on the character #\!.

The #\! reader macro reads input until the #\Newline character followed by a non-#\Space character. If the input consists of one line, it’s transformed into a list and evaluated.

This form:

!+ 1 2 3

transforms into:

(+ 1 2 3)

If the first line is empty, it’s skipped (mostly because of aesthetics):

!
* 1
  2
  3

A multi-line input is transformed the following way:

• Each line followed by indented lines is wrapped into a list together with the rest.
• indented one line comment can be used as a dummy
• A nested invocation of the reader macro is handled in a slightly different way – for the purpose of determining the extent of this nested invocation, the input is cropped from the left up to the corresponding #\! character and then this extracted region is handled.

Some example:

!let !!a "Hello "
      !b "world!"
  !concatenate 'string a b

or equivalently:

!
let !a
        "Hello "
     (b "world!")
  concatenate
    'string a b

Samples

A factorial function:

!defun fact !n
  if !zerop n
    1
    !* n !fact !1- n

a different version:

!defun fact (n)
  if (zerop n)
    1
    * n
      fact
        1-
          n

An implementation of the once-only macro:

!defmacro once-only !(&rest names) &body body
  let !!gensyms !loop for n in names collect !gensym
   `!let !,@!loop for g in gensyms collect `!,g !gensym
      `!let !,,@!loop for g in gensyms for n in names collect ``!,,g ,,n
         ,!let !,@!loop for n in names for g in gensyms collect `!,n ,g
            ,@body