Language Levels

\crexx{} uses language levels to name related REXX-family language surfaces without pretending they are all implemented by the same compiler. The letters are a map, not a compatibility promise.

For the Release 1 beta line, Level B is the supported cREXX language documented by this reference. Other levels are either historical context, project direction, or editor/tooling targets unless their documentation explicitly says that a compiler feature is implemented and tested.

Summary

• use Level B for current cREXX programs
• treat Level C as Classic REXX compatibility work with real DSLSH syntax-highlighting/parser-mode progress, but not yet a release compiler language
• treat Levels E and N as planned DSLSH syntax-highlighting targets for Object REXX and NetRexx source, not as languages that cREXX intends to compile or run
• treat Levels D, G, and L as cREXX direction for future language work

Level B: Current cREXX

Level B is the foundation language for the current compiler, standard library, tooling, and examples. It is deliberately more explicit than Classic REXX:

• source files normally begin with options levelb
• values have known types such as .int, .boolean, .float, .decimal, .string, .binary, .object, and .void
• arrays are declared from typed values, for example .string[]
• reusable code is grouped through namespace, import, and expose
• procedures, methods, factories, and interfaces have checked signatures
• modules compile to .rxbin bytecode and can be linked into deployable images

Level B is used to implement much of the standard library. That is an intentional part of the architecture: the same language available to users is also used to build the platform.

Level Catalogue

The following names are used by the project, but their status is deliberately different:

Level	Meaning	Current project status
Level A	Early compact REXX proof-of-concept foundation.	Historical only. Not a release target.
Level B	Current typed cREXX foundation language.	Implemented and documented as the Release 1 beta user language.
Level C	Classic REXX compatibility.	Not a release compiler language yet. A dedicated DSLSH syntax-highlighting/parser-mode front end now exists as the first concrete compatibility slice.
Level D	A cREXX-compatible extension direction above Classic REXX.	Direction only. Not a release language yet.
Level E	Object REXX / ooRexx relationship point.	Planned only as a DSLSH syntax-highlighting target. cREXX does not plan to compile or run ooRexx as Level E.
Level G	General-purpose modern cREXX direction built on Level B.	Directional, with some real library work such as rxfnsg; not the baseline user language for this release.
Level L	Language-engineering cREXX direction for parser, grammar, AST, and symbol-table work.	Direction only. Not a release language yet.
Level N	NetRexx relationship point: Rexx-family syntax with Java/JVM integration.	Planned only as a DSLSH syntax-highlighting target. cREXX does not plan to compile or run NetRexx as Level N.

DSLSH And Compatibility

DSLSH syntax-highlighting support is allowed to be wider than the compiler. It can help users edit and diagnose REXX-family source without claiming that cREXX can execute that source.

Level C is the first example of that split. The project now has Level C parser-mode and syntax-highlighting work for Classic REXX source, while normal rxc compilation of options levelc remains gated as unsupported. This lets the project build useful editor support and standard-diagnostic experience before committing to a full Classic REXX lowering/runtime path.

Levels E and N should be understood in that same tooling sense. They reserve clear names for Object REXX and NetRexx editor support, but they are not cREXX runtime or source-compatibility commitments.

Defaults

The compiler can be given a default level with rxc --level levelb. The source file wins if it contains an explicit options instruction.

The crexx driver gives headerless top-level scripts a practical default by compiling them as Level B and importing rxfnsb. This convenience does not change the recommendation for reusable source: write the options and import lines explicitly.

Compatibility

Level B borrows from REXX, but it is not a drop-in Classic REXX interpreter. Programs that rely on Classic REXX’s untyped variable model, late binding, or default built-in function visibility usually need small, explicit Level B changes.

The compatibility goals for future levels are important project direction, but this Release 1 beta documentation should not describe future compatibility as current behaviour.