Introduction to G#

G# is a modern, simple, and accessible programming language for the .NET runtime. It draws on the everyday ergonomics of Go, Kotlin, and Swift — small surface, explicit types, sealed hierarchies, nullable handling that the binder helps you with — and compiles down to ordinary managed assemblies that any .NET tool can consume.

If you already know .NET, G# gives you another way to build managed assemblies and call CLR APIs — classes, interfaces, properties, events, delegates, exceptions, async workflows, and so on — under the normal dotnet toolchain. If you are coming from Go, Kotlin, Swift, or TypeScript, much of the syntax will already feel familiar.

How G# runs

Every driver parses, binds, lowers, and emits CIL. SDK projects use the emitter through MSBuild. Direct gsc uses it both with and without /out; without /out, gsc runs the emitted program immediately. File-mode gsi and the interactive REPL also use the emitter. G# function literals can be passed to CLR delegate parameters on these file paths, including bare gsc.

The legacy tree-walking evaluator and its --engine evaluator / GSI_ENGINE=evaluator forms were removed. gsi now accepts only the emit engine choice.

The default emitted target framework is net10.0; the compiler also recognizes net8.0 and net9.0 target framework mappings.

Who G# is for

G# is for people who want a small, predictable language with direct access to the .NET ecosystem. It is especially useful if you want to learn or teach .NET without starting from C#, or if you prefer a modern, Kotlin-/Swift-shaped syntax but still need CLR interop, MSBuild projects, Portable PDBs, and the broader .NET ecosystem.

The language is still growing. The documentation highlights what works today and calls out known implementation limits where they matter.

The 0.4 line adds sound empty collection defaults, full boolean patterns, while let, value-producing block expressions, native CLR rectangular arrays, map iteration, explicit extension receivers, goroutine-safe SyncMap, and SDK hot reload.

Where to start

• Install G# to set up the SDK, templates, or a source-built compiler.
• Quickstart: Hello, G# to compile and run your first program.
• A Tour of G# for a short guided walk through syntax, types, control flow, concurrency, and .NET interop.
• Tutorials for task-oriented walkthroughs.
• Language specification when you need the reference details.