Function compile_polydat 

pub fn compile_polydat(source: &str) -> Result<Box<dyn Kernel>, KernelError>

Compile a .polydat source string under the default options, on the engine those options name — which is Engine::default, the most native form the build has.

This is the way in. The kernel comes back as dyn Kernel, which is the surface every use of a kernel goes through, and the engine is a value the options carry rather than a branch in the code: a caller that wants a different one sets options.engine and calls compile_polydat_kernel_with_options, rather than calling a differently-named function.

Naming an engine is for the callers whose subject is the engine:

• compile_polydat_interpreter for the interpreter’s concrete kernel, when a test or diagnostic needs its own internals, or when it is being used as the semantic oracle a differential test compares a compiled engine against. That is a real need, and it says so by name — it used to be what this entry point quietly returned, which meant a host got the slowest engine by asking for none.
• compile_polydat_with to walk the tiers with one source.