|#lang dssl2||package: dssl2|
DSSL2 is a programming language for data structures students. It’s designed to be simple, providing only the basic elements needed to implement a variety of data structures.
DSSL2 uses alignment and indentation to delimit blocks. In particular, compound statements such as if-elif-else take ⟨block⟩s for each condition, where a ⟨block⟩ can be either one simple statement followed by a newline, or a sequence of statements on subsequent lines that are all indented by four additional spaces. Here is an example of a tree insertion function written using indentation:
#lang dssl2 def insert!(t, k): if empty?(t): new_node(k) elif zero?(random(size(t) + 1)): root_insert!(t, k) elif k < t.key: t.left = insert!(t.left, k) fix_size!(t) t elif k > t.key: t.right = insert!(t.right, k) fix_size!(t) t else: t
Each block follows a colon and newline, and is indented 4 spaces more than the previous line. In particular, the block started by def is indented by 4 spaces, and the elif blocks by 8. When a block is a simple statement, it can be placed on the same line, as in the if and else cases.
Extraneous indentation is an error.