📝Dynamic scoping

As opposed to lexical scoping, dynamic scoping traverses the current invocation stack to find free variables. (Lexical scoping traverses scopes defined by lexical structure of the program.)

Examples

• Emacs Lisp uses dynamic scoping for all variables by default.

  (defvar name "world")
  
  (defun hello ()
    (princ (format "Hello, %s!\n" name)))
  
  (let ((name "blah")) ; name is a local binding here
    (hello))
  
  (hello)
  

  Hello, blah!
  Hello, world!

• Racket: Parameters

• Clojure: dynamic scoping

• “Special” variables in Common Lisp

See also

• Dynamic scoping works badly with laziness

• Dynamic scoping is a better model for global variables

• Reader/State vs dynamic scoping

Backlinks

• 📝 Co-effects
• 📝 Dependency injection
• 📝 Racket: Parameters
• 📝 Reader/State vs dynamic scoping
• 📝 Is effect system only relevant to typed languages?
• 📝 § Effect system
• 📝 Scope vs. Extent
• 📝 In Common Lisp, all global variables are automatically “special” (use dynamic scoping)
• 📝 Dynamic scoping is a better model for global variables
• 📝 Dynamic scoping works badly with laziness
• 📝 Clojure: dynamic scoping
• 📝 § Programming Language