* eval.c (eval_init): Register hash_guni and hash_gisec as intrinsics.

* hash.c (hash_guni, hash_gisec): New functions.
(hash_isec): Bugfix: since gethash was naively used, keys in hash2
associated with the value nil were erroneously omitted from the
intersection.

* hash.h (hash_guni, hash_gisec): Declared.

* txr.1: Documented new functions.

1 files changed, 18 insertions, 5 deletions

diff --git a/txr.1 b/txr.1
index b9a884ff..cc6d127e 100644
--- a/txr.1
+++ b/txr.1
@@ -10594,14 +10594,16 @@ The <result-form> and <body-form>-s are in the scope of an implicit anonymous
 block, which means that it is possible to terminate the execution of
 dohash early using (return) or (return <value>).
 
-.SS Functions hash-uni, hash-diff and hash-isec
+.SS Functions hash-uni, hash-guni, hash-diff, hash-isec and hash-gisec
 
 .TP
 Syntax:
 
   (hash-uni <hash1> <hash2>)
+  (hash-guni <hash1> <hash2>)
   (hash-diff <hash1> <hash2>)
   (hash-isec <hash1> <hash2>)
+  (hash-gisec <hash1> <hash2>)
 
 .TP
 Description:
@@ -10616,10 +10618,16 @@ make-similar-hash operation. If <hash1> has userdata, the resulting hash table
 has the same userdata. If <hash1> has weak keys, the resulting table has weak
 keys, and so forth.
 
-The hash-uni function performs a set union. The resulting hash contains all of the
-keys from <hash1> and all of the keys from <hash2>, and their corresponding values.
-If a key occurs both in <hash1> and <hash2>, then it occurs only once in the
-resulting hash. The value for this common key is the one from <hash2>.
+The hash-uni function performs a set union. The resulting hash contains all of
+the keys from <hash1> and all of the keys from <hash2>, and their corresponding
+values.  If a key occurs both in <hash1> and <hash2>, then it occurs only once
+in the resulting hash. The value for this common key is the one from <hash2>.
+The hash-guni function is similar, except that if a key occurs in both <hash1>
+and <hash2>, then the respective data items from <hash1> and <hash2> for that
+key appear appended together in the resulting hash as if by the append
+function, in that order.  (The hash-guni name is a reference to the group-by
+function. A sequence of data items can be grouped in multiple ways, and then
+the hashes combined with hash-guni.)
 
 The hash-diff function performs a set difference. First, a copy of <hash1> is
 made as if by the copy-has function. Then from this copy, all keys which occur
@@ -10629,6 +10637,11 @@ The hash-isec function performs a set intersection. The resulting hash contains
 only those keys which occur both in <hash1> and <hash2>. The values selected
 for these common keys are those from <hash1>.
 
+The hash-gisec function performs a set intersection similarly to hash-isec.
+However, for each key placed in the resulting hash, the associated data is
+formed by appending together the data item from <hash1> and from <hash2>, in
+that order.
+
 .SH PARTIAL EVALUATION AND COMBINATORS
 
 .SS Operators op and do