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main.go
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main.go
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// Write a program that reads a single expression from the standard input, prompts
// the user to provide values for any variables, then evaluates the expression in
// the resulting environment. Handle all errors gracefully.
package main
import (
"bufio"
"fmt"
"os"
"strconv"
"strings"
"andr.io/ch7/ex7_15/eval"
)
func promptForValue(key string) float64 {
reader := bufio.NewReader(os.Stdin)
fmt.Printf("Enter value for %s: ", key)
r, _ := reader.ReadString('\n')
r = strings.ReplaceAll(r, "\n", "")
value, err := strconv.ParseFloat(r, 64)
if err != nil {
fmt.Printf("%s is not a float value\n", r)
return promptForValue(key)
}
return value
}
func main() {
if len(os.Args) <= 1 {
fmt.Println("usage: evaluate \"{expression}\"")
os.Exit(0)
}
expr, err := eval.Parse(os.Args[1])
if err != nil {
fmt.Fprintf(os.Stderr, "parse: %v\n", err)
os.Exit(1)
}
vars := make(map[eval.Var]bool)
err = expr.Check(vars)
if err != nil {
fmt.Fprintf(os.Stderr, "check: %v\n", err)
os.Exit(1)
}
env := make(map[eval.Var]float64)
for _, v := range expr.Vars() {
env[v] = promptForValue(v.String())
}
result := expr.Eval(env)
fmt.Printf("%s = %s\n", expr, strconv.FormatFloat(float64(result), 'f', -1, 64))
}