Implement gram-related functions.

internal/ngram/ngram.go

@@ -0,0 +1,31 @@
+package ngram
+
+import (
+	"regexp"
+)
+
+var re1, re2 *regexp.Regexp
+
+func init() {
+	re1 = regexp.MustCompile("\\PL+")
+	re2 = regexp.MustCompile("")
+}
+
+func Bigram(s string) []string {
+	bag := split(s)
+
+	r := make([]string, 0)
+	for i := 0; i < len(bag) - 1; i++ {
+		r = append(r, bag[i] + bag[i + 1])
+	}
+
+	return r
+}
+
+func split(s string) []string {
+	bag := make([]string, 0)
+	for _, w := range re1.Split(s, -1) {
+		bag = append(bag, re2.Split(w, -1)...)
+	}
+	return bag
+}