fix: unbound substitutions, explanation tag

internal/cli/arguments.go

@@ -6,13 +6,15 @@ import (
 )
 
 type CLIOptions struct {
-	Input   string
-	Verbose bool
+	Input       string
+	Verbose     bool
+	Explanation bool
 }
 
 func ParseOptions(args []string) (*CLIOptions, error) {
 	// Parse flags and arguments.
 	verbose := flag.Bool("v", false, "Verbosity. If set, the program will print logs.")
+	explanation := flag.Bool("x", false, "Explanation. Whether or not to show all reduction steps.")
 	flag.Parse()
 
 	if flag.NArg() == 0 {
@@ -22,7 +24,8 @@ func ParseOptions(args []string) (*CLIOptions, error) {
 	}
 
 	return &CLIOptions{
-		Input:   flag.Arg(0),
-		Verbose: *verbose,
+		Input:       flag.Arg(0),
+		Verbose:     *verbose,
+		Explanation: *explanation,
 	}, nil
 }