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;;;; derrida.lisp
(in-package #:derrida)
(defmacro with-plist (keys plist &body body)
"KEYS is a list, each member of which is either a symbol or a pair of symbols.
If a member is just a symbol, say KEY, then it is treated as the name
of a symbol-macro (defined using symbol-macrolet) that expands to the
expression (getf PLIST KEY). In this case, KEY is not allowed to be a
keyword symbol.
If a member is a pair of symbols, it is of the form (VAR KEY). Here,
key is a valid key into the PLIST and VAR is the name of the symbol
macrolet that will be bound to (getf PLIST KEY).
EXAMPLE:
(let ((pl
(list 'name \"colin\" :age 40 :|currentJob| :crumb-bum)))
(hq:with-plist (name (age :age) (job :|currentJob|)) pl
(setf age (1+ age))
(format t \"~a the ~a had a birthday, and is now ~a years old~%\"
name job age)
pl))
The above would print out:
colin the CRUMB-BUM had a birthday, and is now 41 years old
And would return
(NAME \"colin\" :AGE 41 :|currentJob| :CRUMB-BUM)"
(let* ((plist-var
(gensym))
(macrolet-bindings
(loop for term in keys
when (consp term )
collect (destructuring-bind (var key) term
`(,var (getf ,plist-var ',key)))
else
collect `(,term (getf ,plist-var ',term)))))
`(let ((,plist-var ,plist)) (symbol-macrolet ,macrolet-bindings ,@body))))
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