//!+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
}
func main() {
handler := func(w http.ResponseWriter, r *http.Request) {
q := r.URL.Query()
d := &data{"", 0.0}
if len(q["expr"]) > 0 {
d.Expr = q["expr"][0]
expr, err := eval.Parse(q["expr"][0])
if err == nil {
d.Result = expr.Eval(eval.Env{})
}
}
calc.Execute(w, d)
}
http.HandleFunc("/", handler)
log.Println("Running server in localhost:8000 ...")
log.Fatal(http.ListenAndServe("localhost:8000", nil))
}
func main() {
exitCode := 0
stdin := bufio.NewScanner(os.Stdin)
fmt.Printf("Expression: ")
stdin.Scan()
expr, err := eval.Parse(stdin.Text())
if err != nil {
fmt.Fprintf(os.Stderr, "bad expression: %s\n", err)
os.Exit(1)
}
fmt.Printf("Variables (<var>=<val>, eg: x=3 y=5 ...): ")
stdin.Scan()
envStr := stdin.Text()
if stdin.Err() != nil {
fmt.Fprintln(os.Stderr, stdin.Err())
os.Exit(1)
}
env := eval.Env{}
assignments := strings.Fields(envStr)
for _, a := range assignments {
fields := strings.Split(a, "=")
if len(fields) != 2 {
fmt.Fprintf(os.Stderr, "bad assignment: %s\n", a)
exitCode = assignment_error
}
ident, valStr := fields[0], fields[1]
val, err := strconv.ParseFloat(valStr, 64)
if err != nil {
fmt.Fprintf(os.Stderr, "bad value for %s, using zero: %s\n", ident, err)
exitCode = assignment_error
}
env[eval.Var(ident)] = val
}
fmt.Println(expr.Eval(env))
os.Exit(exitCode)
}
func main() {
expr, _ := eval.Parse("pow(x + pow(y))")
fmt.Println(expr.String())
}
func main() {
expr, _ := eval.Parse("pow(x,min(1.5,2))")
fmt.Println(expr.Eval(eval.Env{"x": 4}))
}