fixedpoint: add reducer

pkg/fixedpoint/reduce.go

@@ -0,0 +1,16 @@
+package fixedpoint
+
+type Reducer func(prev, curr Value) Value
+
+func Reduce(values []Value, init Value, reducer Reducer) Value {
+	if len(values) == 0 {
+		return init
+	}
+
+	r := reducer(init, values[0])
+	for i := 1; i < len(values); i++ {
+		r = reducer(r, values[i])
+	}
+
+	return r
+}

pkg/fixedpoint/reduce_test.go

@@ -0,0 +1,37 @@
+package fixedpoint
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestReduce(t *testing.T) {
+	type args struct {
+		values  []Value
+		init    Value
+		reducer Reducer
+	}
+	tests := []struct {
+		name string
+		args args
+		want Value
+	}{
+		{
+			name: "simple",
+			args: args{
+				values: []Value{NewFromFloat(1), NewFromFloat(2), NewFromFloat(3)},
+				init:   NewFromFloat(0.0),
+				reducer: func(prev, curr Value) Value {
+					return prev.Add(curr)
+				},
+			},
+			want: NewFromFloat(6),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			assert.Equalf(t, tt.want, Reduce(tt.args.values, tt.args.init, tt.args.reducer), "Reduce(%v, %v, %v)", tt.args.values, tt.args.init, tt.args.reducer)
+		})
+	}
+}

pkg/fixedpoint/slice.go

@@ -0,0 +1,7 @@
+package fixedpoint
+
+type Slice []Value
+
+func (s Slice) Reduce(init Value, reducer Reducer) Value {
+	return Reduce(s, init, reducer)
+}