`string[] args` can't be read at compile time?

[Unazed Spectaculum via Digitalmars-d-learn]

import std.stdio;
import std.file;

void main(string[] args)
{
        if (args.length != 2)
        {
                writeln("usage: ./app <path-to-file>");
                return;
        }

        if (!exists!(args[1]))
        {
                writefln("fatal error: %s doesn't exist", args[1]);
        }
}

Line 13 (if (!exists!(args[1]))) produces error:

'app.d(13): Error: variable args cannot be read at compile time'

With 'dmd -run app.d' compilation command. I've seen another 
Stackoverflow post with a similar issue 
(https://stackoverflow.com/questions/39920780/variable-i-cannot-be-read-at-compile-time) but I don't believe it to be related.

Any help?