From bcecb3b08891a386932eb0942f93ae872703e9e5 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Thu, 13 Feb 2020 12:56:09 -0800
Subject: [PATCH] markov-chains: initial implementation.

---
 extra/markov-chains/authors.txt          |  1 +
 extra/markov-chains/markov-chains.factor | 21 +++++++++++++++++++++
 extra/markov-chains/summary.txt          |  1 +
 3 files changed, 23 insertions(+)
 create mode 100644 extra/markov-chains/authors.txt
 create mode 100644 extra/markov-chains/markov-chains.factor
 create mode 100644 extra/markov-chains/summary.txt

diff --git a/extra/markov-chains/authors.txt b/extra/markov-chains/authors.txt
new file mode 100644
index 0000000000..e091bb8164
--- /dev/null
+++ b/extra/markov-chains/authors.txt
@@ -0,0 +1 @@
+John Benediktsson
diff --git a/extra/markov-chains/markov-chains.factor b/extra/markov-chains/markov-chains.factor
new file mode 100644
index 0000000000..ef2da1986a
--- /dev/null
+++ b/extra/markov-chains/markov-chains.factor
@@ -0,0 +1,21 @@
+! Copyright (C) 2020 John Benediktsson
+! See http://factorcode.org/license.txt for BSD license
+
+USING: assocs assocs.extras assocs.private fry grouping kernel
+math.extras random sequences ;
+
+IN: markov-chains
+
+: transitions ( string -- clumps )
+    { t } { f } surround 2 clump ;
+
+: push-transitions ( table seq -- table )
+    transitions over [
+        [ drop H{ } clone ] cache inc-at
+    ] with-assoc assoc-each ;
+
+: transition-table ( seq -- table )
+    H{ } clone swap [ push-transitions ] each ;
+
+: markov-chain ( table -- seq )
+    t swap '[ _ at weighted-random dup ] [ dup ] produce nip ;
diff --git a/extra/markov-chains/summary.txt b/extra/markov-chains/summary.txt
new file mode 100644
index 0000000000..2eb763e2b2
--- /dev/null
+++ b/extra/markov-chains/summary.txt
@@ -0,0 +1 @@
+Markov chain processes.