Evaluation model

Evaluation in Beskid is callable-centric: functions, methods, closures—with control flow and types checked before lowering. Concurrency is explicit spawn, not hidden schedulers behind await.

Callables and closures

• Functions and methods are the default unit of work.
• Closures capture environment; captures participate in GC rooting when fibers are involved.
• See Lambdas and closures for capture rules.

No async / await

The language rejects reserved async / await tokens. Structured concurrency uses:

• spawn → Fiber<T>
• Join for Result<T, FiberError>
• Channels for cross-fiber payloads
• WaitGroup, Hub for coordination (Concurrency package)

flowchart TB
  main[Main fiber]
  child[spawn child]
  ch[Channel T]
  join[Join handle]
  main --> child
  child --> ch
  main --> join

Compiler anchors

Crate	Role
beskid_analysis	Spawn typing, capture diagnostics
beskid_codegen	fiber_spawn, stack maps
beskid_engine / beskid_runtime	Scheduler, stacks

Area hub

Evaluation

Next

Fibers and spawn