tagbody

(tagbody {tag | form}...)

Evaluates its body forms in order for effect. A bare symbol (or integer) in the body is a go tag: go transfers control to the form after that tag, forward or backward, so loops and state machines can be written with explicit jumps. Falling off the end returns nil.

On the JVM and WASM compilers go is lexical: it must target a tag of a tagbody that lexically encloses it (the interpreter additionally supports dynamic go across function-call boundaries, i.e. a tag established by the caller). A tag reached from inside a nested lambda -- what a handler-bind handler that resumes its loop with a go produces -- is lowered to a non-local exit that re-enters the tagbody at the tag, so it works on every backend; such a program compiles in exception-handling mode, so the wasm runs need wasmtime -W exceptions=y.