From f33c6cfa52c7cdcd5c23fee9e4254ff9fae2779e Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Wed, 13 Feb 2019 06:24:25 -0800
Subject: hash-from-alist: new function.

* hash.c (hash_from_alist_v): New function.
(hash_init): Register hash-from-alist intrinsic.

* hash.h (hash_from_alist_v): Declared.

* txr.1: Documented.
---
 hash.c | 15 +++++++++++++++
 hash.h |  1 +
 txr.1  | 18 +++++++++++++++++-
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/hash.c b/hash.c
index 272e1e2f..6babca4a 100644
--- a/hash.c
+++ b/hash.c
@@ -1195,6 +1195,20 @@ val hash_from_pairs_v(val pairs, struct args *hashv_args)
   return hash_construct(args_get_list(hashv_args), pairs);
 }
 
+val hash_from_alist_v(val alist, struct args *hashv_args)
+{
+  val hash = hashv(hashv_args);
+
+  alist = nullify(alist);
+
+  for (; alist; alist = cdr(alist)) {
+    val pair = car(alist);
+    sethash(hash, car(pair), cdr(pair));
+  }
+
+  return hash;
+}
+
 val hash_list(val keys, struct args *hashv_args)
 {
   val hash = hashv(hashv_args);
@@ -1598,6 +1612,7 @@ void hash_init(void)
   reg_fun(intern(lit("hash"), user_package), func_n0v(hashv));
   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-list"), user_package), func_n1v(hash_list));
   reg_fun(intern(lit("gethash"), user_package), func_n3o(gethash_n, 2));
   reg_fun(intern(lit("inhash"), user_package), func_n3o(inhash, 2));
diff --git a/hash.h b/hash.h
index 6b65daf0..ed94d77a 100644
--- a/hash.h
+++ b/hash.h
@@ -55,6 +55,7 @@ val hashv(struct args *args);
 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_list(val keys, struct args *hashv_args);
 val group_by(val func, val seq, struct args *hashv_args);
 val group_reduce(val hash, val by_fun, val reduce_fun, val seq,
diff --git a/txr.1 b/txr.1
index 7118b588..658fbad0 100644
--- a/txr.1
+++ b/txr.1
@@ -40769,10 +40769,11 @@ function is affected or its hash value under
 is altered, the behavior of subsequent lookup and insertion operations on the
 becomes unspecified.
 
-.coNP Functions @ hash-construct and @ hash-from-pairs
+.coNP Functions @, hash-construct @ hash-from-pairs and @ hash-from-alist
 .synb
 .mets (hash-construct < hash-args << key-val-pairs )
 .mets (hash-from-pairs < key-val-pairs << hash-arg *)
+.mets (hash-from-alist < alist << hash-arg *)
 .syne
 .desc
 The
@@ -40800,6 +40801,21 @@ argument is first, and the
 .meta hash-args
 are passed as trailing variadic arguments, rather than a single list argument.
 
+The
+.code hash-from-alist
+function is similar to
+.codn hash-from-pairs ,
+except that the
+.meta alist
+argument specifies they keys and values as an association list.
+The elements of the list are
+.code cons
+cells, each of whose
+.code car
+is a key, and whose
+.code cdr
+is the value.
+
 .coNP Function @ hash-list
 .synb
 .mets (hash-list < key-list << hash-arg *)
-- 
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