X-Git-Url: https://git.distorted.org.uk/~mdw/sod/blobdiff_plain/284f1fa2ace3e276052ff1bd7d66442500e693da..db6c3279edc260e3e301df1c9b082b374cd002c7:/src/utilities.lisp

diff --git a/src/utilities.lisp b/src/utilities.lisp
index 6663441..72423fd 100644
--- a/src/utilities.lisp
+++ b/src/utilities.lisp
@@ -273,6 +273,22 @@
   "If COND, evaluate BODY as a progn with `it' bound to the value of COND."
   `(let ((it ,cond)) (when it ,@body)))
 
+(export 'aand)
+(defmacro aand (&rest forms)
+  "Like `and', but anaphoric.
+
+   Each FORM except the first is evaluated with `it' bound to the value of
+   the previous one.  If there are no forms, then the result it `t'; if there
+   is exactly one, then wrapping it in `aand' is pointless."
+  (labels ((doit (first rest)
+	     (if (null rest)
+		 first
+		 `(let ((it ,first))
+		    (if it ,(doit (car rest) (cdr rest)) nil)))))
+    (if (null forms)
+	't
+	(doit (car forms) (cdr forms)))))
+
 (export 'acond)
 (defmacro acond (&body clauses &environment env)
   "Like COND, but with `it' bound to the value of the condition.
@@ -430,11 +446,13 @@
   (:documentation
    "Reports an inconsistency in the arguments passed to `merge-lists'.")
   (:report (lambda (condition stream)
-	     (format stream "Merge inconsistency: failed to decide among ~A."
+	     (format stream "Merge inconsistency: failed to decide between ~
+			     ~{~#[~;~A~;~A and ~A~:;~
+				  ~@{~A, ~#[~;and ~A~]~}~]~}"
 		     (merge-error-candidates condition)))))
 
 (export 'merge-lists)
-(defun merge-lists (lists &key pick (test #'eql))
+(defun merge-lists (lists &key pick (test #'eql) (present #'identity))
   "Return a merge of the given LISTS.
 
    The resulting list contains the items of the given LISTS, with duplicates
@@ -442,7 +460,10 @@
    the input LISTS in the sense that if A precedes B in some input list then
    A will also precede B in the output list.  If the lists aren't consistent
    (e.g., some list contains A followed by B, and another contains B followed
-   by A) then an error of type `inconsistent-merge-error' is signalled.
+   by A) then an error of type `inconsistent-merge-error' is signalled.  The
+   offending items are filtered for presentation through the PRESENT function
+   before being attached to the condition, so as to produce a more useful
+   diagnostic message.
 
    Item equality is determined by TEST.
 
@@ -484,7 +505,7 @@
 			      candidates))
 	   (winner (cond ((null leasts)
 			  (error 'inconsistent-merge-error
-				 :candidates candidates))
+				 :candidates (mapcar present candidates)))
 			 ((null (cdr leasts))
 			  (car leasts))
 			 (pick
@@ -812,6 +833,30 @@
 		(setf (,to object) value))))))
 
 ;;;--------------------------------------------------------------------------
+;;; Condition and error utilities.
+
+(export 'designated-condition)
+(defun designated-condition (default-type datum arguments
+			     &key allow-pointless-arguments)
+  "Return the condition designated by DATUM and ARGUMENTS.
+
+   DATUM and ARGUMENTS together are a `condition designator' of (some
+   supertype of) DEFAULT-TYPE; return the condition so designated."
+  (typecase datum
+    (condition
+     (unless (or allow-pointless-arguments (null arguments))
+       (error "Argument list provided with specific condition"))
+     datum)
+    (symbol
+     (apply #'make-condition datum arguments))
+    ((or string function)
+     (make-condition default-type
+		     :format-control datum
+		     :format-arguments arguments))
+    (t
+     (error "Unexpected condition designator datum ~S" datum))))
+
+;;;--------------------------------------------------------------------------
 ;;; CLOS hacking.
 
 (export 'default-slot)