sum and prod take keyfun argument.

* eval.c (eval_init): Adjust registrations of sum and prod to
be binary functions with an optional argument.

* lib.c (nary_op_keyfun, sumv, prodv): New static functions.
(sum, prod): Implement optional keyfun argument via sumv and
prodv helpers.

* lib.h (sum, prod): Declarations updated.

* txr.1: Documentation updated.

1 files changed, 23 insertions, 13 deletions

diff --git a/txr.1 b/txr.1
index cdcf22d6..e3f7ba46 100644
--- a/txr.1
+++ b/txr.1
@@ -35172,34 +35172,46 @@ value of the last division is returned.
 
 .coNP Functions @ sum and @ prod
 .synb
-.mets (sum << num-sequence )
-.mets (prod << num-sequence )
+.mets (sum < sequence <> [ keyfun ])
+.mets (prod < sequence <> [ keyfun ])
 .syne
 .desc
 The
 .code sum
 and
 .code prod
-functions operate on a single argument
-.metn num-sequence ,
-which is a sequence of numbers.
+functions operate on an effective sequence of numbers derived from
+.metn sequence .
+
+If the
+.meta keyfun
+argument is omitted, then the effective sequence is the
+.meta sequence
+argument itself. Otherwise, the effective sequence is understood to be
+a projection mapping of the elements of
+.meta sequence
+through
+.meta keyfun
+as would be calculated by the
+.cblk
+.meti (mapcar < keyfun << sequence )
+.cble
+expression.
 
 The
 .code sum
 function returns the left-associative sum of the elements of
-.meta num-sequence
-calculated as if using the
+the effective sequence calculated as if using the
 .code +
 function.  Similarly, the
 .code prod
 function calculates the left-associative product of the elements of
-.metn num-sequence ,
-as if using the
+the sequence as if using the
 .code *
 function.
 
 If
-.meta num-sequence
+.meta sequence
 is empty then
 .code sum
 returns
@@ -35209,9 +35221,7 @@ and
 returns
 .codn 1 .
 
-If
-.meta num-sequence
-contains one number, then both functions
+If the effective sequence contains one number, then both functions
 return that number.
 
 .coNP Functions @ wrap and @ wrap*