Tier 3 languages can be compiled to WASM modules and they support WASI Preview 1 but there is no way to generate bindings for WIT interfaces.
This restricts them to only expose a single, parameterless run function and they can only access the host functionalities part of WASI Preview 1. (standard IO, files and filesystems, clock, random, cmd args / environment variables).
It is possible to pass input to these functions using the standard input and to get back their standard output as the call’s results, but this function can only be called once for each worker.
Golem provides two special calling conventions for workers implemented with a tier 3 language:
stdio calling convention passes the invocation’s parameters through the worker’s standard input, and parses it’s standard output as JSON, returning as the invocation’s result. A worker after an stdio invocation is no longer usable.stdio-eventloop calling convention makes it possible to implement stateful workers with a tier 3 language but it requires the worker to be implemented as a loop that in each iteration reads a single line containing the invocation parameters as JSON, and before reading the next line is responsible to write the response to the standard output as a single-line JSON.The currently supported Tier 3 languages are