func calc(w http.ResponseWriter, req *http.Request) {
input := req.URL.Query().Get("formula")
fmt.Println(input)
if len(input) < 1 {
w.WriteHeader(http.StatusNotFound)
fmt.Fprintf(w, "formula is not found.")
}
//fmt.Println(input)
e, err := eval.Parse(input)
if err != nil {
log.Fatal(fmt.Errorf("parse error\n%s", err))
}
// vars := eval.ExtractVars(e)
vars := make(map[eval.Var]bool)
if err := e.Check(vars); err != nil {
log.Fatal(err)
}
env := make(eval.Env)
if len(vars) > 0 {
for v := range vars {
s := req.URL.Query().Get(string(v))
env[v], err = strconv.ParseFloat(s, 64)
if err != nil {
log.Fatal(fmt.Errorf("this value is invalid.\n%s", err))
}
}
}
fmt.Fprintf(w, "Answer: %f", e.Eval(env))
}
func calculate(s string) (string, error) {
if s == "" {
return "", nil
}
expr, err := eval.Parse(s)
if err != nil {
return "", err
}
ans := fmt.Sprintf("%.6g", expr.Eval(env))
return ans, nil
}
func Example_expr() {
e, _ := eval.Parse("sqrt(A / pi)")
Display("e", e)
// Output:
// Display e (eval.call):
// e.fn = "sqrt"
// e.args[0].type = eval.binary
// e.args[0].value.op = 47
// e.args[0].value.x.type = eval.Var
// e.args[0].value.x.value = "A"
// e.args[0].value.y.type = eval.Var
// e.args[0].value.y.value = "pi"
}
//!+parseAndCheck
func parseAndCheck(s string) (eval.Expr, error) {
if s == "" {
return nil, fmt.Errorf("empty expression")
}
expr, err := eval.Parse(s)
if err != nil {
return nil, err
}
vars := make(map[eval.Var]bool)
if err := expr.Check(vars); err != nil {
return nil, err
}
for v := range vars {
if v != "x" && v != "y" && v != "r" {
return nil, fmt.Errorf("undefined variable: %s", v)
}
}
return expr, nil
}