From 0f35aac318d36b3eabcd90e12ba6bb13f4fffa1f Mon Sep 17 00:00:00 2001
From: Yutaka Ichibangase <yichiban@gmail.com>
Date: Fri, 18 Mar 2022 21:41:57 +0900
Subject: [PATCH] add evaluable functor: max

---
 engine/number.go      | 38 +++++++++++++++++++++++++++
 engine/number_test.go | 61 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)

diff --git a/engine/number.go b/engine/number.go
index 05e2dd6..d87d5c7 100644
--- a/engine/number.go
+++ b/engine/number.go
@@ -823,6 +823,44 @@ func IntFloorDiv(x, y Number) (Number, error) {
 	}
 }
 
+// Max returns the maximum of x or y.
+func Max(x, y Number) (Number, error) {
+	switch x := x.(type) {
+	case Integer:
+		switch y := y.(type) {
+		case Integer:
+			if x < y {
+				return y, nil
+			}
+			return x, nil
+		case Float:
+			if floatItoF(x) < y {
+				return y, nil
+			}
+			return x, nil
+		default:
+			return nil, ErrUndefined
+		}
+	case Float:
+		switch y := y.(type) {
+		case Integer:
+			if x < floatItoF(y) {
+				return y, nil
+			}
+			return x, nil
+		case Float:
+			if x < y {
+				return y, nil
+			}
+			return x, nil
+		default:
+			return nil, ErrUndefined
+		}
+	default:
+		return nil, ErrUndefined
+	}
+}
+
 // Comparison
 
 func eqF(x, y Float) bool {
diff --git a/engine/number_test.go b/engine/number_test.go
index 1585ac6..0fd626d 100644
--- a/engine/number_test.go
+++ b/engine/number_test.go
@@ -1410,6 +1410,67 @@ func TestIntFloorDiv(t *testing.T) {
 	})
 }
 
+func TestMax(t *testing.T) {
+	t.Run("integer", func(t *testing.T) {
+		t.Run("integer", func(t *testing.T) {
+			r, err := Max(Integer(1), Integer(2))
+			assert.NoError(t, err)
+			assert.Equal(t, Integer(2), r)
+
+			r, err = Max(Integer(1), Integer(1))
+			assert.NoError(t, err)
+			assert.Equal(t, Integer(1), r)
+		})
+
+		t.Run("float", func(t *testing.T) {
+			r, err := Max(Integer(1), Float(2))
+			assert.NoError(t, err)
+			assert.Equal(t, Float(2), r)
+
+			r, err = Max(Integer(1), Float(1))
+			assert.NoError(t, err)
+			assert.Equal(t, Integer(1), r)
+		})
+
+		t.Run("not a number", func(t *testing.T) {
+			_, err := Max(Integer(1), mockNumber{})
+			assert.Equal(t, ErrUndefined, err)
+		})
+	})
+
+	t.Run("float", func(t *testing.T) {
+		t.Run("integer", func(t *testing.T) {
+			r, err := Max(Float(1), Integer(2))
+			assert.NoError(t, err)
+			assert.Equal(t, Integer(2), r)
+
+			r, err = Max(Float(1), Integer(1))
+			assert.NoError(t, err)
+			assert.Equal(t, Float(1), r)
+		})
+
+		t.Run("float", func(t *testing.T) {
+			r, err := Max(Float(1), Float(2))
+			assert.NoError(t, err)
+			assert.Equal(t, Float(2), r)
+
+			r, err = Max(Float(1), Float(1))
+			assert.NoError(t, err)
+			assert.Equal(t, Float(1), r)
+		})
+
+		t.Run("not a number", func(t *testing.T) {
+			_, err := Max(Float(1), mockNumber{})
+			assert.Equal(t, ErrUndefined, err)
+		})
+	})
+
+	t.Run("not a number", func(t *testing.T) {
+		_, err := Max(mockNumber{}, Integer(1))
+		assert.Equal(t, ErrUndefined, err)
+	})
+}
+
 type mockNumber struct {
 	mock.Mock
 }