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(elisp)Specification Examples

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Specification Examples
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   It may be easier to understand Edebug specifications by studying the
examples provided here.

   A `let' special form has a sequence of bindings and a body.  Each of
the bindings is either a symbol or a sublist with a symbol and optional
expression.  In the specification below, notice the `gate' inside of
the sublist to prevent backtracking once a sublist is found.

     (def-edebug-spec let
       ((&rest
         &or symbolp (gate symbolp &optional form))
        body))

   Edebug uses the following specifications for `defun' and `defmacro'
and the associated argument list and `interactive' specifications.  It
is necessary to handle interactive forms specially since an expression
argument it is actually evaluated outside of the function body.

     (def-edebug-spec defmacro defun) ; Indirect ref to `defun' spec.
     (def-edebug-spec defun
       (&define name lambda-list
                [&optional stringp]   ; Match the doc string, if present.
                [&optional ("interactive" interactive)]
                def-body))
     
     (def-edebug-spec lambda-list
       (([&rest arg]
         [&optional ["&optional" arg &rest arg]]
         &optional ["&rest" arg]
         )))
     
     (def-edebug-spec interactive
       (&optional &or stringp def-form))    ; Notice: `def-form'

   The specification for backquote below illustrates how to match
dotted lists and use `nil' to terminate recursion.  It also illustrates
how components of a vector may be matched.  (The actual specification
defined by Edebug does not support dotted lists because doing so causes
very deep recursion that could fail.)

     (def-edebug-spec ` (backquote-form))   ; Alias just for clarity.
     
     (def-edebug-spec backquote-form
       (&or ([&or "," ",@"] &or ("quote" backquote-form) form)
            (backquote-form . [&or nil backquote-form])
            (vector &rest backquote-form)
            sexp))