1 files changed, 43 insertions, 0 deletions
diff --git a/op.go b/op.go
new file mode 100644
index 0000000..ab57a84
--- /dev/null
+++ b/op.go
@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"math"
+)
+
+// parseOp returns a closure that performs the specified arithmetic operation,
+// or OpError if op is not a valid operator.
+func parseOp(op byte) (func(lhs *float64, rhs float64), error) {
+	switch op {
+	case '+':
+		return func(lhs *float64, rhs float64) { *lhs += rhs }, nil
+	case '-':
+		return func(lhs *float64, rhs float64) { *lhs -= rhs }, nil
+	case '*':
+		return func(lhs *float64, rhs float64) { *lhs *= rhs }, nil
+	case '/':
+		return func(lhs *float64, rhs float64) {
+			if rhs != 0 {
+				*lhs /= rhs
+			}
+		}, nil
+	case '%':
+		return func(lhs *float64, rhs float64) {
+			if rhs != 0 {
+				*lhs = float64(int64(*lhs) % int64(rhs))
+			}
+		}, nil
+	case '^':
+		return func(lhs *float64, rhs float64) { *lhs = math.Pow(*lhs, rhs) }, nil
+	}
+	return nil, OpError{op}
+}
+
+// OpError records an invalid arithmetic operator.
+type OpError struct {
+	c byte
+}
+
+func (e OpError) Error() string {
+	return fmt.Sprintf("invalid operator: %c", e.c)
+}