Layout

Layouts, inherited from Haskell, are a convenient and flexible basis for whitespace-sensitive syntax. At the core, a production Layout S P parses token S, followed by a sequence of P productions, following a few simple rules:

• Each P must be indented further than the leading token S.

• All elements P must be aligned with one another; i.e., every P is equally indented.

• Lines indented further than the P elements are folded into the preceeding element.

compare & contrast with Python's INDENT/DEDENT tokens

Use in SydML

I decided that SydML will use layouts in the future, only after considering the following pros:

• I have Haskellbrain.

• For this kind of task, Tree-sitter requires a hand-written lexer in C. As I haven't written any C in ages, I figured it would be fun. }:)

Further reading

• Section 2.7 of The Haskell 98 Report

• The Python Language Reference on lexical analysis