1 files changed, 63 insertions, 0 deletions
diff --git a/calc.go b/calc.go
new file mode 100644
index 0000000..8afc43a
--- /dev/null
+++ b/calc.go
@@ -0,0 +1,63 @@
+package main
+
+import (
+	"strconv"
+	"strings"
+)
+
+type Calculator struct {
+	stack Stack
+	buf   string
+}
+
+// swap swaps the values of the buffer and the bottom element of the stack. If
+// the buffer is empty this simply pops from the stack. If the stack is empty,
+// this simply pushes to the stack.
+func (c *Calculator) swap() {
+	st := c.stack.pop()
+	if con := parseConstant(c.buf); con != nil {
+		c.stack.push(*con)
+	} else if f, err := strconv.ParseFloat(c.buf, 64); err == nil {
+		c.stack.push(f)
+	}
+	if st != nil {
+		c.buf = strings.TrimSpace(printNum(*st))
+	} else {
+		c.buf = ""
+	}
+}
+
+// negate negates the number in the buffer, if any; or the bottom number on the
+// stack, if any.
+func (c *Calculator) negate() {
+	if con := parseConstant(c.buf); con != nil {
+		c.buf = strings.TrimSpace(printNum(-*con))
+	} else if f, err := strconv.ParseFloat(c.buf, 64); err == nil {
+		c.buf = strings.TrimSpace(printNum(-f))
+	} else if len(c.buf) == 0 && len(c.stack) > 0 {
+		c.stack[len(c.stack)-1] = -c.stack[len(c.stack)-1]
+	}
+}
+
+// performOp performs the specified arithmetic operation and returns nil or
+// OpError if op is not a valid operator.
+func (c *Calculator) performOp(op byte) error {
+	if len(c.stack) < 1 {
+		return nil
+	}
+
+	fn, err := parseOp(op)
+	if err != nil {
+		return err
+	}
+
+	if con := parseConstant(c.buf); con != nil {
+		fn(&c.stack[len(c.stack)-1], *con)
+	} else if fl, err := strconv.ParseFloat(c.buf, 64); err == nil {
+		fn(&c.stack[len(c.stack)-1], fl)
+	} else if len(c.stack) > 1 {
+		fn(&c.stack[len(c.stack)-2], *c.stack.pop())
+	}
+	c.buf = ""
+	return nil
+}