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package main
import (
"fmt"
"strconv"
)
type Stack []float64
type Calculator struct {
stack Stack
buf string
}
// 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
}
// 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
}
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)
}
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