* arith.c (divi): Support one-argument form.

Use "/" name in error reporting, not "divi".

* eval.c (eval_init): Change registration of / so only
one argument is required out of two.

* txr.1: Document one-argument division.

4 files changed, 26 insertions, 8 deletions

diff --git a/ChangeLog b/ChangeLog
index ff4b0b7d..ae8e9302 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 2014-07-20  Kaz Kylheku  <kaz@kylheku.com>
 
+	* arith.c (divi): Support one-argument form.
+	Use "/" name in error reporting, not "divi".
+
+	* eval.c (eval_init): Change registration of / so only
+	one argument is required out of two.
+
+	* txr.1: Document one-argument division.
+
+2014-07-20  Kaz Kylheku  <kaz@kylheku.com>
+
 	* genvim.txr: Fixed highlighting issues in numbers followed by newline.
 
 	* txr.vim: Regenerated.
diff --git a/arith.c b/arith.c
index 14d3d0e2..7051ddb8 100644
--- a/arith.c
+++ b/arith.c
@@ -946,13 +946,20 @@ static val to_float(val func, val num)
 
 val divi(val anum, val bnum)
 {
-  double a = c_flo(to_float(lit("divi"), anum));
-  double b = c_flo(to_float(lit("divi"), bnum));
+  if (missingp(bnum)) {
+    double b = c_flo(to_float(lit("/"), anum));
+    if (b == 0.0)
+      uw_throw(numeric_error_s, lit("/: division by zero"));
+    return flo(1.0 / b);
+  } else {
+    double a = c_flo(to_float(lit("/"), anum));
+    double b = c_flo(to_float(lit("/"), bnum));
 
-  if (b == 0.0)
-    uw_throw(numeric_error_s, lit("divi: division by zero"));
+    if (b == 0.0)
+      uw_throw(numeric_error_s, lit("/: division by zero"));
 
-  return flo(a / b);
+    return flo(a / b);
+  }
 }
 
 val zerop(val num)
diff --git a/eval.c b/eval.c
index 6e596272..0cd9b73d 100644
--- a/eval.c
+++ b/eval.c
@@ -3594,7 +3594,7 @@ void eval_init(void)
   reg_fun(intern(lit("abs"), user_package), func_n1(abso));
   reg_fun(intern(lit("trunc"), user_package), func_n2(trunc));
   reg_fun(intern(lit("mod"), user_package), func_n2(mod));
-  reg_fun(intern(lit("/"), user_package), func_n2(divi));
+  reg_fun(intern(lit("/"), user_package), func_n2o(divi, 1));
   reg_fun(intern(lit("expt"), user_package), func_n0v(exptv));
   reg_fun(intern(lit("exptmod"), user_package), func_n3(exptmod));
   reg_fun(intern(lit("isqrt"), user_package), func_n1(isqrt));
diff --git a/txr.1 b/txr.1
index b3f4b3b8..5ffacc85 100644
--- a/txr.1
+++ b/txr.1
@@ -10807,7 +10807,7 @@ A character may not be an operand of multiplication.
 .TP
 Syntax:
 
-  (/ <dividend> <divisor>)
+  (/ [<dividend>] <divisor>)
   (trunc <dividend> <divisor>)
   (mod <dividend> <divisor>)
 
@@ -10816,7 +10816,8 @@ Description:
 The arguments to these functions are numbers. Characters are not permitted.
 
 The / function performs floating-point division. Each operands is first
-converted to floating-point type, if necessary.
+converted to floating-point type, if necessary. If <dividend> is omitted,
+then it is taken to be 1.0 and the function performs a reciprocal.
 
 The trunc function performs a division of <dividend> by <divisor> whose result
 is truncated to integer toward zero. If both operands are integers, then an