Rule 8.20

A function a host file can call through an import of its module is an exported function that is not an entry point, is not generic, takes no function, has a host value (Rule 8.21) for each parameter and for its result, and reaches, through the calls of its body, no binding, no workgroup variable and no builtin only a GPU computes (a derivative, a barrier, an atomic, an implicit-LOD texture sample). An exported @compute entry is callable too, and a full-screen @fragment entry draws into a canvas, as Rule 8.24 says; a kernel function (Rule 8.22) is callable, asynchronously, as this rule’s last paragraph says; a vertex entry is not callable yet. An exported constant and an enum are values of the host face, and an exported struct is a type of it, as is a struct another file declares where an export’s signature names it; what a module re-exports from a shader file it imports (Rule 3.9) is one of its exports; every other export is declared never in the host view, with the reason and the work that adds it, so a call of one is a type error at the host’s own line.