[Zero]

From Wikipedia:

A more recent (circa 2003) variant is I-expressions, which use indentation to indicate parentheses implicitly, and are thus in some ways intermediate between S-expressions and M-expressions. I-expressions were introduced in Scheme Request For Implementation 49 as an auxiliary syntax for Scheme, but they have not been widely adopted.

Example from https://srfi.schemers.org/srfi-49/srfi-49.html

define (fac x)
    if (= x 0) 1
        * x fac (- x 1)

let
    group
        foo (+ 1 2)
        bar (+ 3 4)
    + foo bar


I like it. It's elegant, isn't it?

[8pla.net]

"which use indentation to indicate parentheses implicitly"

Is that what it's for, indentation, to take the place of parentheses?

[Zero]

That's right. Cool thing is you still have a choice whether to use indentation or parens as you see fit.