From 19fb18a343d88621ebab989539a3463b1ffbba7d Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 24 Jan 2017 10:44:10 -0800
Subject: New memp function for searching a plist.

* eval.c (eval_init): Register memp intrinsic.

* lib.c (memp): New function.

* lib.h (memp): Declared.

* txr.1: Documented.
---
 eval.c |  1 +
 lib.c  |  9 +++++++++
 lib.h  |  1 +
 txr.1  | 48 +++++++++++++++++++++++++++++++++++++++++++-----
 4 files changed, 54 insertions(+), 5 deletions(-)

diff --git a/eval.c b/eval.c
index e21ec820..8adea078 100644
--- a/eval.c
+++ b/eval.c
@@ -5800,6 +5800,7 @@ void eval_init(void)
   reg_fun(intern(lit("copy-cons"), user_package), func_n1(copy_cons));
   reg_fun(intern(lit("copy-alist"), user_package), func_n1(copy_alist));
   reg_fun(intern(lit("prop"), user_package), func_n2(getplist));
+  reg_fun(intern(lit("memp"), user_package), func_n2(memp));
   reg_fun(intern(lit("merge"), user_package), func_n4o(merge_wrap, 2));
   reg_fun(intern(lit("sort"), user_package), func_n3o(sort, 1));
   reg_fun(intern(lit("shuffle"), user_package), func_n1(shuffle));
diff --git a/lib.c b/lib.c
index fdba27d2..40cae588 100644
--- a/lib.c
+++ b/lib.c
@@ -2855,6 +2855,15 @@ val getplist_f(val list, val key, loc found)
   return nil;
 }
 
+val memp(val key, val plist)
+{
+  for (; plist; plist = cddr(plist)) {
+    if (car(plist) == key)
+      return plist;
+  }
+  return nil;
+}
+
 val proper_plist_to_alist(val list)
 {
   list_collect_decl (out, ptail);
diff --git a/lib.h b/lib.h
index 425acd01..80163f3c 100644
--- a/lib.h
+++ b/lib.h
@@ -611,6 +611,7 @@ val proper_list_p(val obj);
 val length_list(val list);
 val getplist(val list, val key);
 val getplist_f(val list, val key, loc found);
+val memp(val key, val plist);
 val proper_plist_to_alist(val list);
 val improper_plist_to_alist(val list, val boolean_keys);
 val num(cnum val);
diff --git a/txr.1 b/txr.1
index dd7b816e..198cca4b 100644
--- a/txr.1
+++ b/txr.1
@@ -18184,16 +18184,16 @@ function applied to the corresponding
 element of the input list.
 
 .SS* Property Lists
-.coNP Function @ prop
-.synb
-.mets (prop < plist << key )
-.syne
-.desc
 A property list a flat list of even length consisting of interleaved
 pairs of property names (usually symbols) and their values (arbitrary
 objects). An example property list is (:a 1 :b "two") which contains
 two properties, :a having value 1, and :b having value "two".
 
+.coNP Function @ prop
+.synb
+.mets (prop < plist << key )
+.syne
+.desc
 The
 .code prop
 function searches property list
@@ -18211,6 +18211,44 @@ found, or due to the property being present with a
 .code nil
 value.
 
+The indicators in
+.meta plist
+are compared with
+.meta key
+using
+.code eq
+equality, allowing them to be symbols, characters or
+.code fixnum
+integers.
+
+.coNP Function @ memp
+.synb
+.mets (memp < key << plist )
+.syne
+.desc
+The
+.code memp
+function searches property list
+.meta plist
+for key
+.metn key ,
+using
+.code eq
+equality.
+
+If the key is found, then the entire suffix of
+.meta plist
+beginning with the indicator is returned, such that the first
+element of the returned list is
+.meta key
+and the second element is the property value.
+
+Note the reversed argument convention relative to the
+.code prop
+function, harmonizing with functions in the
+.code member
+family.
+
 .SS* List Sorting
 
 Note: these functions operate on lists. The principal sorting function
-- 
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