81 lines
1.4 KiB
Go
81 lines
1.4 KiB
Go
package calc
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import (
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"errors"
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"fmt"
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. "github.com/vektah/goparsify"
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)
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var (
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value Parser
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sumOp = Chars("+-", 1, 1)
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prodOp = Chars("/*", 1, 1)
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groupExpr = Map(And("(", sum, ")"), func(n Node) Node {
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return Node{Result: n.Child[1].Result}
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})
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number = Map(NumberLit(), func(n Node) Node {
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switch i := n.Result.(type) {
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case int64:
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return Node{Result: float64(i)}
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case float64:
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return Node{Result: i}
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default:
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panic(fmt.Errorf("unknown value %#v", i))
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}
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})
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sum = Map(And(prod, Kleene(And(sumOp, prod))), func(n Node) Node {
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i := n.Child[0].Result.(float64)
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for _, op := range n.Child[1].Child {
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switch op.Child[0].Token {
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case "+":
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i += op.Child[1].Result.(float64)
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case "-":
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i -= op.Child[1].Result.(float64)
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}
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}
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return Node{Result: i}
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})
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prod = Map(And(&value, Kleene(And(prodOp, &value))), func(n Node) Node {
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i := n.Child[0].Result.(float64)
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for _, op := range n.Child[1].Child {
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switch op.Child[0].Token {
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case "/":
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i /= op.Child[1].Result.(float64)
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case "*":
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i *= op.Child[1].Result.(float64)
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}
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}
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return Node{Result: i}
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})
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Y = Maybe(sum)
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)
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func init() {
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value = Any(number, groupExpr)
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}
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func Calc(input string) (float64, error) {
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result, remaining, err := ParseString(Y, input)
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if err != nil {
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return 0, err
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}
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if remaining != "" {
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return result.(float64), errors.New("left unparsed: " + remaining)
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}
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return result.(float64), nil
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}
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