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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[len(c.stack)-1])
c.stack = c.stack[:len(c.stack)-1]
}
c.buf = ""
return nil
}
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