How do I format an EK9 source file?

← Code Formatting · Ref: Q622

EK9 has a built-in code formatter, similar to gofmt for Go or rustfmt for Rust. Use the -f flag to format a single file.

BASIC USAGE

  ek9 -f myfile.ek9

This parses the file first, then rewrites it in canonical format. The file must be valid EK9 (parseable) for -f to work.

WHAT IT CHANGES

- Normalises indentation to canonical two-space indent.
- Standardises whitespace around operators and keywords.
- Aligns block structure consistently.
- Removes trailing whitespace.
- Ensures consistent blank-line usage between constructs.

WHAT IT PRESERVES

- Comments (both doc-comments and inline comments) are preserved.
- Blank lines that separate logical sections are maintained.
- The semantic meaning of the code is never altered.

WHEN TO USE -f
Use -f after writing or editing a file manually. It is safe to run repeatedly because the output is idempotent: formatting an already-formatted file produces the same file.

See Q623 for formatting all project files. See Q624 for force-formatting unparseable files. See Q625 for why EK9 enforces a standard format. See Q626 for integrating formatting into your workflow. See Q16 for indentation rules.

Example

defines module qa.codeformatting.single

  defines function

    <?-
      A function that would be reformatted by ek9 -f
      if written with inconsistent spacing.
      After formatting, indentation is canonical.
    -?>
    greet() as pure
      -> name as String
      <- message as String: `Hello, ${name}!`

    calculateArea() as pure
      ->
        width as Float
        height as Float
      <-
        area as Float: width * height

  defines program

    FormatDemo()
      stdout <- Stdout()

      greeting <- greet("World")
      stdout.println(greeting)

      roomArea <- calculateArea(4.5, 3.2)
      stdout.println(`Area: ${roomArea}`)

Common mistakes

E50001 — Removing the variable declaration means later references to the variable become unresolved, triggering E50001. See ek9 -h E50001 for details.

Incorrect:

greet("World")

Correct:

greeting <- greet("World")

Coming from another language?

Go: gofmt built into toolchain, universally adopted, single canonical style. Rust: rustfmt (cargo fmt) built into toolchain. Python: black (external, opinionated), autopep8, yapf. Java: google-java-format, spotless (all external plugins). JavaScript: prettier (external). EK9: ek9 -f built into compiler binary, same philosophy as gofmt (one true format, no configuration).

Keywords: migrate, rustfmt, whitespace, format, style, gofmt, indent, auto-format, canonical, formatter