Hello Bitcoin-Dev,

I hope this isn't out of line, but I joined the mailing list to try to
start a discussion on adding opcodes to make Script Turing Pseudo-Complete
as Wright suggested is possible.

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In line with Wright's suggestion, I propose adding a return stack alongside
the, already existing, control stack.

The principle opcodes (excluding conditional versions of call and
return_from) needed are

OP_DEFINITION_START FunctionName:  The code that follows is the definition
of a new function to be named TransactionSenderAddress.FunctionName.  If
this function name is already taken, the transaction is marked invalid.
Within the transaction, the function can be called simply as FunctionName.

OP_DEFINITION_END:  This ends a function definition

OP_FUNCTION_NAME FunctionName:  Gives the current transaction the name
FunctionName (this is necessary to build recursive functions)

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OP_CALL Namespace.FunctionName Value TransactionFee:  This marks the
transaction as valid.  It also pushes the current execution location onto
the return stack, debits the calling transaction by the TransactionFee and
Value, and creates a new transaction specified by Namespace.FunctionName
with both stacks continued from before (this may be dangerous, but I see no
way around it) with the specified value.

OP_RETURN_FROM_CALL_AND_CONTINUE:  This pops the top value off the return
stack and continues from the specified location with both stacks in tact.

---

It would also be useful if a transaction can create another transaction
arbitrarily, so to prepare for that, I additionally propose

OP_NAMESPACE:  Pushes the current namespace onto the control stack

This, combined with the ability to make new transactions arbitrarily would
allow a function to pay its creator.



I understand that this isn't all that is needed, but I think it's a start.
I hope this proposal has met you all well,

Luke Durback