Here I am adding a source code formatting tool, geas -f. The purpose of this
tool is similar to gofmt, it indents the code applies a canonical style.
End-of-line comments are automatically aligned to the same column across the
entire document.

To make this work, the AST is extended with comment nodes. Lines containing just
a comment are represented by a dedicated comment statement. For comments that
follow a statement on the same line, the AST node of the statement tracks the
attached comment node.

The AST has seen a few general simplifications in the process: names of
statement types have been improved and all statements now share a base object
type containing the position and attached comment. Parenthesized expressions are
now wrapped in a GroupNode so the parentheses will be kept by the formatter.