Use Rust and Ruby Syntax

By the end of this chapter, you will have navigated syntax, selected a complete definition, and undone a syntax indentation change.

Current built-in syntax support covers saved .rs and .rb paths. Matching is case-sensitive. Other suffixes and pathless buffers retain ordinary text editing. Syntax analysis does not require or start a language server.

Prepare a Rust File

From the repository root, save this text as syntax.rs:

fn greet() {
let message = "hello";
println!("{message}");
}

Open it in the nonmodal profile:

env -u RUBYOPT -u RUBYLIB -u GEM_HOME -u GEM_PATH \
  cargo run --locked -p rur-editor --bin rur-terminal-proof -- \
  --profile nonmodal syntax.rs

Keywords and comments use syntax styles from the selected theme. Active regions and search matches retain their own emphasis.

Navigate and Select Structure

Move to the second line with Down. Through Alt-x, choose move-syntax-up. Point moves to the enclosing block; repeating moves toward the outer function. move-syntax-down enters a named child. move-syntax-forward and move-syntax-backward visit named siblings. A missing target leaves point in place. These commands have no factory key bindings.

Return to the second line with move-buffer-start, then Down. Invoke select-syntax. The ordinary active region selects the syntax node at point. Repeating the command expands an exact node selection to its enclosing named node when one exists. Ctrl-G deactivates the region.

Invoke select-definition from inside the function. The region covers the outer function. Repeating retains that definition. This command selects an outer definition; it does not look up a symbol in another file.

Indent and Undo

Cancel the active region, return to the second line, and choose indent-syntax through Alt-x. The current line gains leading indentation according to the active editing policy. Ctrl-Z restores the original unindented line; Ctrl-X Ctrl-Z reapplies the change.

A linear region applies indentation to its intersected lines as one undoable change. Blank lines, comments, strings, and malformed lines retain their bytes. Save deliberately with Ctrl-X Ctrl-S, then leave through Ctrl-Q.

Try Ruby and Plain Text

After leaving the editor, save this text as syntax.rb:

class Greeting
  def message
    "hello"
  end
end

Start another editor process with the earlier command, replacing syntax.rs with syntax.rb. Inside message, select-definition selects the outer class. The same syntax movement, selection, and indentation command names apply. A .txt file with identical content remains ordinary text: syntax commands preserve point and selection when analysis is unavailable.

See Syntax Movement, Definition Selection, and Syntax Indentation for the exact target and preservation rules.

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