From 506575ce91cbed2c11c5484d140b12004fe6a92b Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 1 May 2023 11:40:09 -0700
Subject: hash: new function, hash-props.

We don't have a function in the hash table module which can
create a populated hash table in one step without requiring
the caller to create auxiliary lists. This new function fills
that gap, albeit with some limitations.

* hash.c (hash_props): New function.
(hash_init): Register hash-props intrinsic.

* tests/010/hash.tl: New tests.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.
---
 hash.c             | 21 +++++++++++++++++++++
 hash.h             |  1 +
 stdlib/doc-syms.tl |  1 +
 tests/010/hash.tl  |  7 +++++++
 txr.1              | 21 +++++++++++++++++++++
 5 files changed, 51 insertions(+)

diff --git a/hash.c b/hash.c
index 1b85e01f..f258bcb7 100644
--- a/hash.c
+++ b/hash.c
@@ -1613,6 +1613,26 @@ val hash_from_alist_v(val alist, struct args *hashv_args)
   return hash;
 }
 
+val hash_props(struct args *plist)
+{
+  val self = lit("hash-props");
+  args_decl_constsize(args, ARGS_MIN);
+  val hash = hashv(args);
+  cnum index = 0;
+
+  while (args_two_more(plist, index)) {
+    val key = args_get(plist, &index);
+    val value = args_get(plist, &index);
+    sethash(hash, key, value);
+  }
+
+  if (args_more(plist, index))
+    uw_throwf(error_s, lit("~a: unpaired ~s argument"),
+              self, args_get(plist, &index), nao);
+
+  return hash;
+}
+
 val hash_list(val keys, struct args *hashv_args)
 {
   val hash = hashv(hashv_args);
@@ -2121,6 +2141,7 @@ void hash_init(void)
   reg_fun(hash_construct_s, func_n2(hash_construct));
   reg_fun(intern(lit("hash-from-pairs"), user_package), func_n1v(hash_from_pairs_v));
   reg_fun(intern(lit("hash-from-alist"), user_package), func_n1v(hash_from_alist_v));
+  reg_fun(intern(lit("hash-props"), user_package), func_n0v(hash_props));
   reg_fun(intern(lit("hash-list"), user_package), func_n1v(hash_list));
   reg_fun(intern(lit("hash-zip"), user_package), func_n2v(hash_zip));
   reg_fun(intern(lit("gethash"), user_package), func_n3o(gethash_n, 2));
diff --git a/hash.h b/hash.h
index 22c1bd0e..cc1a0f1d 100644
--- a/hash.h
+++ b/hash.h
@@ -82,6 +82,7 @@ val hashl(val args);
 val hash_construct(val hashl_args, val pairs);
 val hash_from_pairs_v(val pairs, struct args *hashv_args);
 val hash_from_alist_v(val alist, struct args *hashv_args);
+val hash_props(struct args *plist);
 val hash_list(val keys, struct args *hashv_args);
 val hash_zip(val keys, val vals, struct args *hashv_args);
 val group_by(val func, val seq, struct args *hashv_args);
diff --git a/stdlib/doc-syms.tl b/stdlib/doc-syms.tl
index 2c9c14b1..029cecbd 100644
--- a/stdlib/doc-syms.tl
+++ b/stdlib/doc-syms.tl
@@ -953,6 +953,7 @@
       ("hash-pairs" "N-00C9B125")
       ("hash-peek" "N-0225209D")
       ("hash-proper-subset" "N-024ACBBB")
+      ("hash-props" "N-026628B3")
       ("hash-reset" "N-0225209D")
       ("hash-revget" "N-02FBE776")
       ("hash-subset" "N-024ACBBB")
diff --git a/tests/010/hash.tl b/tests/010/hash.tl
index 7f662b51..558688af 100644
--- a/tests/010/hash.tl
+++ b/tests/010/hash.tl
@@ -20,3 +20,10 @@
                                                      (#\s 3) (#\u 1) (#\v 1)
                                                      (#\y 1))
   [group-reduce (hash) evenp + (range 1 10) 0] #H(() (t 30) (nil 25)))
+
+(mtest
+  (hash-props) #H(())
+  (hash-props 1 2) #H(() (1 2))
+  (hash-props 1 2 'a 'b) #H(() (1 2) (a b))
+  (hash-props 1) :error
+  (hash-props 1 2 'a) :error)
diff --git a/txr.1 b/txr.1
index 232c174a..6927bd13 100644
--- a/txr.1
+++ b/txr.1
@@ -55442,6 +55442,27 @@ is longer than
 .metn value-seq ,
 then the excess keys are ignored, and vice versa.
 
+.coNP Function @ hash-props
+.synb
+.mets (hash-props >> { key << value }*)
+.syne
+.desc
+The
+.code hash-props
+function constructs a populated hash table without requiring
+the caller to construct a list of entries. The hash table
+contents are specified as direct arguments.
+
+The
+.code hash-props
+function requires an even number of arguments, which
+are interleaved key-value pairs.
+
+The returned hash table is
+.codn equal -based,
+and no parameters are available for customizing any of
+its properties, such as weakness.
+
 .coNP Function @ hash-update
 .synb
 .mets (hash-update < hash << function )
-- 
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