Info Catalog cl: Function Bindings cl: Variable Bindings

cl: Macro Bindings

 
 4.3.3 Macro Bindings
 --------------------
 
 These forms create local macros and “symbol macros”.
 
  -- Macro: cl-macrolet (bindings...) forms...
      This form is analogous to ‘cl-flet’, but for macros instead of
      functions.  Each BINDING is a list of the same form as the
      arguments to ‘cl-defmacro’ (i.e., a macro name, argument list, and
      macro-expander forms).  The macro is defined accordingly for use
      within the body of the ‘cl-macrolet’.
 
      Because of the nature of macros, ‘cl-macrolet’ is always lexically
      scoped.  The ‘cl-macrolet’ binding will affect only calls that
      appear physically within the body FORMS, possibly after expansion
      of other macros in the body.
 
  -- Macro: cl-symbol-macrolet (bindings...) forms...
      This form creates “symbol macros”, which are macros that look like
      variable references rather than function calls.  Each BINDING is a
      list ‘(VAR EXPANSION)’; any reference to VAR within the body FORMS
      is replaced by EXPANSION.
 
           (setq bar '(5 . 9))
           (cl-symbol-macrolet ((foo (car bar)))
             (cl-incf foo))
           bar
                ⇒ (6 . 9)
 
      A ‘setq’ of a symbol macro is treated the same as a ‘setf’.  I.e.,
      ‘(setq foo 4)’ in the above would be equivalent to ‘(setf foo 4)’,
      which in turn expands to ‘(setf (car bar) 4)’.
 
      Likewise, a ‘let’ or ‘let*’ binding a symbol macro is treated like
      a ‘cl-letf’ or ‘cl-letf*’.  This differs from true Common Lisp,
      where the rules of lexical scoping cause a ‘let’ binding to shadow
      a ‘symbol-macrolet’ binding.  In this package, such shadowing does
      not occur, even when ‘lexical-binding’ is ‘t’.  (This behavior
      predates the addition of lexical binding to Emacs Lisp, and may
      change in future to respect ‘lexical-binding’.)  At present in this
      package, only ‘lexical-let’ and ‘lexical-let*’ will shadow a symbol
      macro.  Obsolete Lexical Binding.
 
      There is no analogue of ‘defmacro’ for symbol macros; all symbol
      macros are local.  A typical use of ‘cl-symbol-macrolet’ is in the
      expansion of another macro:
 
           (cl-defmacro my-dolist ((x list) &rest body)
             (let ((var (cl-gensym)))
               (list 'cl-loop 'for var 'on list 'do
                     (cl-list* 'cl-symbol-macrolet
                               (list (list x (list 'car var)))
                               body))))
 
           (setq mylist '(1 2 3 4))
           (my-dolist (x mylist) (cl-incf x))
           mylist
                ⇒ (2 3 4 5)
 
      In this example, the ‘my-dolist’ macro is similar to ‘dolist’
      (Iteration) except that the variable ‘x’ becomes a true
      reference onto the elements of the list.  The ‘my-dolist’ call
      shown here expands to
 
           (cl-loop for G1234 on mylist do
                 (cl-symbol-macrolet ((x (car G1234)))
                   (cl-incf x)))
 
      which in turn expands to
 
           (cl-loop for G1234 on mylist do (cl-incf (car G1234)))
 
      Loop Facility, for a description of the ‘cl-loop’ macro.
      This package defines a nonstandard ‘in-ref’ loop clause that works
      much like ‘my-dolist’.
 

Info Catalog cl: Function Bindings cl: Variable Bindings