1 files changed, 75 insertions, 0 deletions
diff --git a/markov.go b/markov.go
new file mode 100644
index 0000000..bdba9ce
--- /dev/null
+++ b/markov.go
@@ -0,0 +1,75 @@
+// This program implements a Markov chain algorithm. Given some input text,
+// it generates pseudo-random phrases by repeatedly choosing a suffix word that
+// follows the current multi-word prefix.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"math/rand"
+	"os"
+)
+
+const (
+	nPref  = 2     // number of prefix words
+	maxGen = 10000 // maximum number of words to generate
+)
+
+type Prefix struct {
+	words [nPref]string
+}
+
+// push advances the prefix to contain `word'.
+func (p *Prefix) push(word string) {
+	if nPref < 1 {
+		return
+	} else if nPref == 1 {
+		p.words[0] = word
+	} else {
+		p.words = [nPref]string(append(p.words[1:], word))
+	}
+}
+
+// StateMap associates each multi-word Prefix with a list of suffix words.
+// The starting state is an empty Prefix{} with the suffix list containing
+// the first word of the input text. The ending state is the last few words
+// of the input text with an empty suffix list.
+type StateMap map[Prefix][]string
+
+func main() {
+	states := build(os.Stdin)
+	generate(states, maxGen)
+}
+
+// build populates a StateMap with words read from `in'.
+func build(in io.Reader) StateMap {
+	states := make(StateMap)
+	prefix := Prefix{}
+
+	scanner := bufio.NewScanner(in)
+	scanner.Split(bufio.ScanWords)
+	for scanner.Scan() {
+		suffix := scanner.Text()
+		states[prefix] = append(states[prefix], suffix)
+		prefix.push(suffix)
+	}
+
+	states[prefix] = []string{} // ending state
+
+	return states
+}
+
+// generate produces at most `nWords' of output, one word per line.
+func generate(states StateMap, nWords int) {
+	prefix := Prefix{}
+	for i := 0; i < maxGen; i++ {
+		suffixes := states[prefix]
+		if len(suffixes) <= 0 { // ending state
+			return
+		}
+		suffix := suffixes[rand.Intn(len(suffixes))]
+		fmt.Println(suffix)
+		prefix.push(suffix)
+	}
+}