[TCLCORE] Just not my Type?

[Colin M. <col...@ya...>]

Dear All,

In trying to answer sebres's criticism of the compiled code efficiency 
in my tip 676 implementation, I wrote some kludgy, ad-hoc compile-time 
type-checking.  This allows me to skip doing a run-time check that a 
value is numeric when it comes from a command that always gives numeric 
results.  I'm now wondering if a more general type-checking facility for 
Tcl could be worth exploring.

My kludge could be extended to specify the return types and argument 
types for those built-in commands where this is possible.  E.g. 
`llength` requires a list argument and returns an integer.  A variant of 
`proc` could be introduced where one can specify argument and return types.

Also we could have a facility to declare a variable with a fixed type in 
a similar way to how Tip 677 allows declaring a variable to be 
constant.  A typed variable would have to be initialised with a legal 
value of that type, and could only be modified to another value which 
can be converted to that same type.

Then, for example, an arithmetic expression whose variables were all 
known to be doubles could be evaluated without all the type-checking and 
conversion logic which is currently needed, perhaps giving a significant 
speedup.  It should also be possible to do better error reporting, e.g. 
if the increment passed to `incr` has been declared as double, this 
error can be reported at compile time.  Such errors could be picked up 
if and when the code is compiled, even if that specific command is not 
executed.  This would address another of the perennial complaints 
against Tcl.

Any thoughts, too un-Tcl-ish perhaps???

Season's Greetings,
Colin.