1 files changed, 41 insertions, 0 deletions
diff --git a/share/txr/stdlib/txr-case.tl b/share/txr/stdlib/txr-case.tl
new file mode 100644
index 00000000..2e0c5979
--- /dev/null
+++ b/share/txr/stdlib/txr-case.tl
@@ -0,0 +1,41 @@
+(defmacro txr-if (name args input : then else)
+  (let ((syms (keep-if [andf true symbolp [notf keywordp] [notf (op eq t)]]
+                       args))
+        (arg-exprs [mapcar [iffi symbolp (ret ^',@1)] args])
+        (result (gensym "res-"))
+        (bindings (gensym "bindings-"))
+        (insym (gensym "input-")))
+    ^(let* ((,insym ,input)
+            (,result (match-fun ',name (list ,*arg-exprs)
+                                (if (stringp ,insym) (list ,insym) ,insym)
+                                nil)))
+       (if ,result
+         (let ((,bindings (car ,result)))
+           (let (,*[mapcar (ret ^(,@1 (cdr (assoc ',@1 ,bindings))))
+                           syms])
+             ,then))
+         ,else))))
+
+(defmacro txr-when (name args input . body)
+  ^(txr-if ,name ,args ,input (progn ,*body)))
+
+(defmacro txr-case-impl (sym . clauses)
+  (tree-case clauses
+    (((name args . body) . other-clauses)
+     (if (eq name t) :
+       ^(txr-if ,name ,args ,sym
+          (progn ,*body)
+          (txr-case-impl ,sym ,*other-clauses))))
+    (((sym . rest) . other-clauses)
+     (if (eq sym t)
+       (if other-clauses
+         (error "txr-case: clauses after (t ...) clause ignored")
+         ^(progn ,*rest))
+       (error "txr-case: bad syntax: ~s" (car clauses))))
+    (atom
+       (error "txr-case: unexpected atom in syntax: ~s" atom))))
+
+(defmacro txr-case (input-expr . clauses)
+  (let ((input (gensym "input-")))
+    ^(let ((,input ,input-expr))
+       (txr-case-impl ,input ,*clauses))))