Tcl added first-class hash maps in the form of dictionaries several years ago. Tcl also added coroutines and a native object system in the past decade. Tcl ha

Tcl added first-class hash maps in the form of dictionaries several years ago. Tcl also added coroutines and a native object system in the past decade. Tcl has variable trace hooks which can be called whenever an attempt is made to change a variable's value, the hook can block the change, making any so-traced variable effectively immutable. (see: https://rosettacode.org/wiki/Enforced_immutability#Tcl https://rosettacode.org/wiki/Enforced_immutability#Tcl )