[TCLCORE] On type checking variables

[<apn...@ya...>]

(Probably a question for Donal, but sending to the list in case folks have
ideas / opinions for or against)

 

The [const] command implementation in Tcl 9 essentially bars writes to
specified variables. How hard would it be to loosen this constraint
mechanism to instead only bar certain writes, for example, writing values
that do not match a specified type? So, in Tcl 9

 

const x 42

set x 43 <- disallowed

 

Similarly, 

 

Int32 x 42

Set x 43 <- allowed

Set x abc <- disallowed

 

Etc.

 

A generalized constraint mechanism will introduce many complexities but just
type check does not seem hard to implement.

 

The motivation by the way is to simplify interfaces to external API's in
other languages and data exchange by not having to carry typing tags.

 

Any comments on (a) feasibility, and (b) implications, if any, for Tcl
semantics ?

 

/Ashok