Comal: Support for CHAIN

[stevewpalmer]

This is not yet implemented as it would be limited to compiled programs as the Comal run-time has no standalone functionality to dynamically compile Comal source. I suspect other Comal compilers have the same restriction but it would be worth looking into. I don't believe the CHAIN command is used widely enough to warrant refactoring to add source-level chaining.

Assuming this is limited to compiled executables then it should be simple enough to add if we approach this in the same way as forking a new process.

What is the user experience when running CHAIN from the interpreter? In standard Comal interpreters, the program in memory is replaced by the one being CHAIN'ed. The official Comal spec states:

Programs already in main storage will be deleted when the CHAIN statement is invoked. Only programs stored by means of the SAVE command can be retrieved via CHAIN.

This won't actually be the case here. In theory, CHAIN from within the interpreter could load, compile and run Comal source directly but this divergence between behaviours within the interpreter and stand-alone executables isn't something that should be sanctioned as it would break consistency.