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|
package calc
import (
"fmt"
. "github.com/vektah/goparsify"
)
var (
value Parser
sumOp = Chars("+-", 1, 1)
prodOp = Chars("/*", 1, 1)
groupExpr = Seq("(", sum, ")").Map(func(n *Result) {
n.Result = n.Child[1].Result
})
number = NumberLit().Map(func(n *Result) {
switch i := n.Result.(type) {
case int64:
n.Result = float64(i)
case float64:
n.Result = i
default:
panic(fmt.Errorf("unknown value %#v", i))
}
})
sum = Seq(prod, Some(Seq(sumOp, prod))).Map(func(n *Result) {
i := n.Child[0].Result.(float64)
for _, op := range n.Child[1].Child {
switch op.Child[0].Token {
case "+":
i += op.Child[1].Result.(float64)
case "-":
i -= op.Child[1].Result.(float64)
}
}
n.Result = i
})
prod = Seq(&value, Some(Seq(prodOp, &value))).Map(func(n *Result) {
i := n.Child[0].Result.(float64)
for _, op := range n.Child[1].Child {
switch op.Child[0].Token {
case "/":
i /= op.Child[1].Result.(float64)
case "*":
i *= op.Child[1].Result.(float64)
}
}
n.Result = i
})
y = Maybe(sum)
)
func init() {
value = Any(number, groupExpr)
}
func calc(input string) (float64, error) {
result, err := Run(y, input)
if err != nil {
return 0, err
}
return result.(float64), nil
}
|
