Tcl added this relatively recently. They use the "tailcall" command, which immediately replaces the stack frame of the current function with one for the new fun

Tcl added this relatively recently. They use the "tailcall" command, which immediately replaces the stack frame of the current function with one for the new function. If I recall correctly, it doesn't do any checks for whether or not the call is actually a tail-call, so if you do something like return [expr [tailcall foo] + 1] the return and expr simply never get executed, producing incorrect results (which I guess is slightly better than a potential stack overflow, since even the most basic of tests will pick up on the missing +1).