status: final (2013-09-09)
keywords: Reader Syntax
This SRFI describes a set of syntax extensions for Scheme, called sweet-expressions (t-expressions), that has the same descriptive power as s-expressions but is designed to be easier for humans to read. The sweet-expression syntax enables the use of syntactically-meaningful indentation to group expressions (similar to Python), and it builds on the infix and traditional function notation defined in SRFI-105 (curly-infix-expressions). Unlike nearly all past efforts to improve s-expression readability, sweet-expressions are general (the notation is independent from any underlying semantic) and homoiconic (the underlying data structure is clear from the syntax). This notation was developed by the “Readable Lisp S-expressions Project” and can be used for both programs and data.
Sweet-expressions can be considered a set of
additional abbreviations, just as 'x already abbreviates
(quote x). Sweet-expressions and traditionally formatted
s-expressions can be freely mixed; this provides backwards compatibility,
simplifies transition, and enables developers to maximize readability.
Here is an example of a sweet-expression and its equivalent s-expression
(note that a sweet-expression reader would accept either
format):
| sweet-expression | s-expression |
|---|---|
define fibfast(n) ; Typical function notation
if {n < 2} ; Indentation, infix {...}
n ; Single expr = no new list
fibup n 2 1 0 ; Simple function calls
|
(define (fibfast n)
(if (< n 2)
n
(fibup n 2 1 0)))
|