SRFI 119: wisp: simpler indentation-sensitive scheme

by Arne Babenhauserheide

status: final (2015-06-23)

keywords: Reader Syntax


This SRFI describes a simple syntax which allows making scheme easier to read for newcomers while keeping the simplicity, generality and elegance of s-expressions. Similar to SRFI 110, SRFI 49 and Python it uses indentation to group expressions. Like SRFI 110 wisp is general and homoiconic.

Different from its predecessors, wisp only uses the absolute minimum of additional syntax-elements which are required for writing and exchanging arbitrary code-structures. As syntax elements it only uses a colon surrounded by whitespace, the period followed by whitespace as first code-character on the line and optional underscores followed by whitespace at the beginning of the line.

It resolves a limitation of SRFI 110 and SRFI 49, both of which force the programmer to use a single argument per line if the arguments to a procedure need to be continued after a procedure-call.

Wisp expressions can include arbitrary s-expressions and as such provide backwards compatibility.

wisp s-exp
define : factorial n
__  if : zero? n
____   . 1
____   * n : factorial (- n 1)

display : factorial 5
(define (factorial n)
    (if (zero? n)
       (* n (factorial (- n 1)))))

(display (factorial 5))