in

The keyword is used in conjunction with other keywords to refer to the incoming direction.

1.  together with the keyword function it is used to designate parameters that may only be read inside the parameterized function;
2. together with the keyword port it is used to designate messages or procedures that a given port may only receive;
3.  together with the keyword signature it is used to designate parameters that may only be read by the called procedure.

Related keywords:

• function
• port
• signature

BNF definition of in (sense 1 and 3)
BNF definition of in (sense 2)