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package main
import (
"fmt"
"math"
)
// Op is a binary operator.
type Op func(lhs, rhs float64) float64
// parseOp parses a binary operator, returning a function that performs the operation, or
// OpError if op is not a valid operator.
func parseOperator(op byte) (Op, error) {
switch op {
case '+':
return func(lhs, rhs float64) float64 { return lhs + rhs }, nil
case '-':
return func(lhs, rhs float64) float64 { return lhs - rhs }, nil
case '*':
return func(lhs, rhs float64) float64 { return lhs * rhs }, nil
case '/':
return func(lhs, rhs float64) float64 {
if rhs != 0 {
return lhs / rhs
}
return lhs
}, nil
case '%':
return func(lhs, rhs float64) float64 {
if rhs != 0 {
return float64(int64(lhs) % int64(rhs))
}
return lhs
}, nil
case '^':
return func(lhs, rhs float64) float64 { return math.Pow(lhs, rhs) }, nil
}
return nil, OperatorErr{op}
}
// OperatorErr records an invalid arithmetic operator.
type OperatorErr struct {
c byte
}
func (e OperatorErr) Error() string {
return fmt.Sprintf("invalid operator: %c", e.c)
}
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