diff --git a/rules.go b/rules.go
new file mode 100644
index 0000000..b937e5b
--- /dev/null
+++ b/rules.go
@@ -0,0 +1,44 @@
+package main
+
+import "strings"
+
+type evaluator interface {
+	Eval(content string) bool
+}
+type sexp struct {
+	op   string
+	args []evaluator
+}
+
+func (s sexp) Eval(content string) bool {
+	switch s.op {
+	case "not":
+		if len(s.args) == 0 {
+			return true
+		}
+		return !s.args[0].Eval(content)
+
+	case "and":
+		for _, a := range s.args {
+			if !a.Eval(content) {
+				return false
+			}
+		}
+		return true
+
+	case "or":
+		for _, a := range s.args {
+			if a.Eval(content) {
+				return true
+			}
+		}
+		return false
+	}
+	return false
+}
+
+type matcher string
+
+func (m matcher) Eval(content string) bool {
+	return strings.Contains(content, string(m))
+}
diff --git a/rules_test.go b/rules_test.go
new file mode 100644
index 0000000..cf25cc7
--- /dev/null
+++ b/rules_test.go
@@ -0,0 +1,38 @@
+package main
+
+import "testing"
+
+func TestSexp(t *testing.T) {
+
+	sexp := sexp{
+		op: "and",
+		args: []evaluator{
+			sexp{op: "or", args: []evaluator{matcher("too"), matcher("boo")}},
+			sexp{op: "not", args: []evaluator{matcher("crumble")}},
+		},
+	}
+
+	if sexp.Eval("footle boolte") != true {
+		t.Errorf("expected true, have false")
+	}
+
+	if sexp.Eval("boo crumble") != false {
+		t.Errorf("expected false, have true")
+	}
+}
+
+func TestSexpNot(t *testing.T) {
+
+	sexp := sexp{
+		op:   "not",
+		args: []evaluator{matcher("footle")},
+	}
+
+	if sexp.Eval("boolte tootle") != true {
+		t.Errorf("expected true, have false")
+	}
+
+	if sexp.Eval("footle mcdootle") != false {
+		t.Errorf("expected false, have true")
+	}
+}