What do you consider a mainstream language? Rust uses it in their standard library[0]. Haskell uses it[1]. Lisp seems to have originated the concept in the f

What do you consider a mainstream language? Rust uses it in their standard library[0]. Haskell uses it[1]. Lisp seems to have originated the concept in the form of box diagrams[2]. F# uses it [3]. I think it might be a functional programming thing. [0] https://doc.rust-lang.org/std/boxed/struct.Box.html https://doc.rust-lang.org/std/boxed/struct.Box.html [1] https://downloads.haskell.org/~ghc/6.12.1/docs/html/users_guide/primitives.html https://downloads.haskell.org/~ghc/6.12.1/docs/html/users_gu... [2] https://www.gnu.org/software/emacs/manual/html_node/elisp/Box-Diagrams.html https://www.gnu.org/software/emacs/manual/html_node/elisp/Bo... [3] https://fsharpforfunandprofit.com/posts/cli-types/ https://fsharpforfunandprofit.com/posts/cli-types/