A tree representation typically represented with indentations.
The syntax uses indentation to group expressions, and has no special cases for semantic constructs of the language. It can be used both for program and data input. It also allows mixing with S-expressions freely, giving the programmer the ability to layout the code as to maximize readability.
The s-exp (* (+ 1 2) (/ 3 4)), can be represented as the following i-exp:
* + 1 2 / 3 4
Example
define
fac x
if
= x 0
1
* x
fac
- x 1