Add plural function.

Closes #12

README.md

@@ -100,6 +100,8 @@ parse, it returns the time unaltered. See `time.ParseDuration` for info on durat
 - cat: Concatenate strings, separating them by spaces. `cat $a $b $c`.
 - indent: Indent a string using space characters. `indent 4 "foo\nbar"` produces "    foo\n    bar"
 - replace: Replace an old with a new in a string: `$name | replace " " "-"`
+- plural: Choose singular or plural based on length: `len $fish | plural
+  "one anchovy" "many anchovies"`
 
 ### String Slice Functions:
 

functions.go

@@ -54,6 +54,7 @@ String Functions
 	- cat: Concatenate strings, separating them by spaces. `cat $a $b $c`.
 	- indent: Indent a string using space characters. `indent 4 "foo\nbar"` produces "    foo\n    bar"
 	- replace: Replace an old with a new in a string: `$name | replace " " "-"`
+	- plural: Choose singular or plural based on length: `len $fish | plural "one anchovy" "many anchovies"`
 
 String Slice Functions:
 
@@ -275,6 +276,7 @@ var genericMap = map[string]interface{}{
 	"cat":      cat,
 	"indent":   indent,
 	"replace":  replace,
+	"plural":   plural,
 
 	// Wrap Atoi to stop errors.
 	"atoi":  func(a string) int { i, _ := strconv.Atoi(a); return i },
@@ -735,3 +737,10 @@ func indent(spaces int, v string) string {
 func replace(old, new, src string) string {
 	return strings.Replace(src, old, new, -1)
 }
+
+func plural(one, many string, count int) string {
+	if count == 1 {
+		return one
+	}
+	return many
+}

functions_test.go

@@ -381,6 +381,17 @@ func TestReplace(t *testing.T) {
 	}
 }
 
+func TestPlural(t *testing.T) {
+	tpl := `{{$num := len "two"}}{{$num}} {{$num | plural "1 char" "chars"}}`
+	if err := runt(tpl, "3 chars"); err != nil {
+		t.Error(err)
+	}
+	tpl = `{{len "t" | plural "cheese" "%d chars"}}`
+	if err := runt(tpl, "cheese"); err != nil {
+		t.Error(err)
+	}
+}
+
 func TestTuple(t *testing.T) {
 	tpl := `{{$t := tuple 1 "a" "foo"}}{{index $t 2}}{{index $t 0 }}{{index $t 1}}`
 	if err := runt(tpl, "foo1a"); err != nil {