revised U command: fail if no argument is provided

 * there is no reasonable default value for U
 * omitting the parameter for U might be a frequent programming error
 * U can be colon-modified now, in which case it may be used
 * to check for the presence of arguments in macros

3 files changed, 32 insertions, 7 deletions

diff --git a/lib/fnkeys.tes b/lib/fnkeys.tes
index c40be40..94c886d 100644
--- a/lib/fnkeys.tes
+++ b/lib/fnkeys.tes
@@ -18,11 +18,11 @@
 @[DC]{}
 @[HOME]{(-(.-(0L.))M#c}
 @[END]{(-(.-(:L"S.-1|Z'))M#c}
-@[NPAGE]{(-(.-(M#p.))M#c}
+@[NPAGE]{(-(.-(1M#p.))M#c}
 @[PPAGE]{(-(.-(-M#p.))M#c}
 @[LEFT]{(-M#c}
 @[SLEFT]{(-(.--W.)M#c}
-@[RIGHT]{(M#c}
+@[RIGHT]{(1M#c}
 @[SRIGHT]{(-(.-W.)M#c}
 @[UP]{(-(.-B.)M#c}
 @[DOWN]{(-(.-L.)M#c}
diff --git a/src/parser.h b/src/parser.h
index c19ef14..9cc8f07 100644
--- a/src/parser.h
+++ b/src/parser.h
@@ -179,6 +179,14 @@ public:
 			   : Error("Syntax error \"%c\" (%d)", chr, chr) {}
 	};
 
+	class ArgExpectedError : public Error {
+	public:
+		ArgExpectedError(const gchar *cmd)
+			        : Error("Argument expected for <%s>", cmd) {}
+		ArgExpectedError(gchar cmd)
+			        : Error("Argument expected for <%c>", cmd) {}
+	};
+
 	class MoveError : public Error {
 	public:
 		MoveError(const gchar *cmd)
diff --git a/src/qregisters.cpp b/src/qregisters.cpp
index 1a7ba34..115cd36 100644
--- a/src/qregisters.cpp
+++ b/src/qregisters.cpp
@@ -617,21 +617,38 @@ StateGetQRegInteger::got_register(QRegister &reg)
 }
 
 /*$
- * [n]Uq -- Set Q-Register integer
+ * nUq -- Set Q-Register integer
+ * -Uq
+ * [n]:Uq -> Success|Failure
  *
  * Sets the integer-part of Q-Register <q> to <n>.
- * If <n> is omitted, the sign prefix is implied.
+ * \(lq-U\(rq is equivalent to \(lq-1U\(rq, otherwise
+ * the command fails if <n> is missing.
+ *
+ * If the command is colon-modified, it returns a success
+ * boolean if <n> or \(lq-\(rq is given.
+ * Otherwise it returns a failure boolean and does not
+ * modify <q>.
  *
  * The register is defined if it does not exist.
  */
-/** @bug perhaps it's better to imply 0! */
 State *
 StateSetQRegInteger::got_register(QRegister &reg)
 {
 	BEGIN_EXEC(&States::start);
 
-	reg.undo_set_integer();
-	reg.set_integer(expressions.pop_num_calc());
+	expressions.eval();
+	if (expressions.args() || expressions.num_sign < 0) {
+		reg.undo_set_integer();
+		reg.set_integer(expressions.pop_num_calc());
+
+		if (eval_colon())
+			expressions.push(SUCCESS);
+	} else if (eval_colon()) {
+		expressions.push(FAILURE);
+	} else {
+		throw ArgExpectedError('U');
+	}
 
 	return &States::start;
 }