David A. Wheeler's Blog

Mon, 14 Oct 2013

Readable Lisp version 1.0.0 released!

Lisp-based languages have been around a long time. They have some interesting properties, especially when you want to write programs that analyze or manipulate programs. The problem with Lisp is that the traditional Lisp notation - s-expressions - is notoriously hard to read.

I think I have a solution to the problem. I looked at past (failed) solutions and found that they generally failed to be general or homoiconic. I then worked to find notations with these key properties. My solution is a set of notation tiers that make Lisp-based languages much more pleasant to work with. I’ve been working with many others to turn this idea of readable notations into a reality. If you’re interested, you can watch a short video or read our proposed solution.

The big news is that we have reached version 1.0.0 in the readable project. We now have an open source software (MIT license) implementation for both (guile) Scheme and Common Lisp, as well as a variety of support tools. The Scheme portion implements the SRFI-105 and SRFI-110 specs, which we wrote. One of the tools, unsweeten, makes it possible to process files in other Lisps as well.

So what do these tools do? Fundamentally, they implement the 3 notation tiers we’ve created: curly-infix-expressions, neoteric-expressions, and sweet-expressions. Sweet-expressions have the full set of capabilities.

Here’s an example of (awkward) traditional s-expression format:

(define (factorial n)
  (if (<= n 1)
    (* n (factorial (- n 1)))))

Here’s the same thing, expressed using sweet-expressions:

define factorial(n)
  if {n <= 1}
    {n * factorial{n - 1}}

I even briefly mentioned sweet-expressions in my PhD dissertation “Fully Countering Trusting Trust through Diverse Double-Compiling” (see section A.3).

So if you are interested in how to make Lisp-based languages easier to read, watch our short video about the readable notations or download the current version of the readable project. We hope you enjoy them.

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