swift-tcl from Flightaware is a two-way bridge that allows writing Tcl extensions in Swift and calling Tcl from Swift.

Swift Tcl is a bridge between Swift and Tcl, providing deep interoperability between the two languages.

Swift developers can use Tcl to make new and powerful ways to interact with, debug, construct automated testing for, and orchestrate the high level activities of their applications.

Tcl developers can use Swift to gets its sweet, expressive, high performance, scripting-language-like capabilities wherever they would like while retaining all of their existing code.

Either can go in for a lot or a little.

Developers can extend Tcl by writing new commands in Swift and extend Swift by writing new commands in Tcl. Tcl commands written in Swift are tiny and simple compared to those written in C.