GHC.Types.ForeignCall

contains the calling convention

foreign export ccall foo :: ty

Import of a C entity

• the two strings specifying a header file or library may be empty, which indicates the absence of a header or object specification (both are not used in the case of CWrapper and when CFunction has a dynamic target)

• the calling convention is irrelevant for code generation in the case of CLabel, but is needed for pretty printing

• Safety is irrelevant for CLabel and CWrapper

The first argument of the import is the name of a function pointer (an Addr#). Used when importing a label as "foreign import ccall "dynamic" ..."

In this current Unit.

In that other Unit.

Binds to a value, a zero-arity function.

Binds to a function with arity of at least one.

Might invoke Haskell GC, or do a call back, or switch threads, etc. So make sure things are tidy before the call. Additionally, in the threaded RTS we arrange for the external call to be executed by a separate OS thread, i.e., _concurrently_ to the execution of other Haskell threads.

Like PlaySafe, but additionally the worker thread running this foreign call may be unceremoniously killed, so it must be scheduled on an unbound thread.

None of the above can happen; the call will return without interacting with the runtime system at all. Specifically:

• No GC

• No call backs

• No blocking

• No precise exceptions