Add: with-plists; initial commit

3 files changed, 57 insertions, 0 deletions

diff --git a/derrida.asd b/derrida.asd
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+++ b/derrida.asd
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+;;;; derrida.asd
+
+(asdf:defsystem #:derrida
+  :description "Macros for desctructuring common data structures."
+  :author "Colin Okay <colin@cicadas.surf>"
+  :license  "GPL-3.0"
+  :version "0.0.1"
+  :serial t
+  :components ((:file "package")
+               (:file "derrida")))
diff --git a/derrida.lisp b/derrida.lisp
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+++ b/derrida.lisp
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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))))
diff --git a/package.lisp b/package.lisp
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+++ b/package.lisp
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+;;;; package.lisp
+
+(defpackage #:derrida
+  (:use #:cl)
+  (:export #:with-plist))