How to invert bool false/true in alias compose?

[Marcone via Digitalmars-d-learn]

import std;

alias cmd = compose!(to!bool, wait, spawnShell, to!string);
void main(){
        writeln(cmd("where notepad.exe"));
}


Result:

C:\Windows\System32\notepad.exe
C:\Windows\notepad.exe
false


The result show "false" because good spawnshell command return 0 
and 0 to bool is false. But I want to invert false to true to get 
true or false if command success.