Roadmap

go-ruby-prettyprint/prettyprint is grown test-first, each capability differential-tested against MRI rather than built in isolation. Ruby's PrettyPrint layout engine — the deterministic, interpreter-independent Wadler/Lindig algorithm — is complete.

Stage	What	Status
Groups & width-fitting	Groups print flat when they fit and break at their breakables when they overflow maxwidth — the exact break_outmost_groups / depth-bucketed GroupQueue algorithm, so nested groups break outermost-first.	Done
Breakables	breakable(sep, width) line-break hints that emit their separator when the line is not broken, with the width argument for multibyte/proportional separators.	Done
Nesting & indentation	nest(indent) and the group(indent, …) indent argument, with a pluggable genspace block (default DefaultGenSpace).	Done
Open/close text & fill mode	group(indent, open, close) bracketing text counted toward the fit decision, and fill_breakable, where each break is decided individually.	Done
Single-line formatter	singleline_format, where breakables become their separator text and nothing ever breaks; custom newline and maxwidth.	Done
Differential oracle & coverage	A shared corpus run through this package and a generated PrettyPrint.format / singleline_format script, output asserted identical; deterministic golden + white-box tests alone hold 100% coverage, gofmt + go vet clean, green across all six 64-bit Go arches and three OSes.	Done

Documented out-of-scope boundaries

These are deliberate, recorded so the module's surface is unambiguous:

• The engine, not the inspector. This module is the layout engine only. The pp object inspector — walking an object graph and emitting the text/group/breakable calls — stays host-side in rbgo. This library is the backend it binds to.
• No interpreter. The library implements the deterministic algorithm; it never runs arbitrary Ruby. Anything that needs a live binding is the consumer's job — that is why rbgo binds this module rather than the reverse.
• Reference is reference Ruby (MRI). Byte-for-byte conformance targets MRI's prettyprint.rb, pinned by the differential oracle.
• Standalone & reusable. The module has no dependency on the Ruby runtime; the dependency runs the other way.

See Usage & API for the surface and Why pure Go for the engine / inspector split.