Dmd is a separate code base and is not available in a regular D build.
You have to provide it and then link it in.
The easiest way to do it is by using dmd-fe via dub.
Examples: https://github.com/dlang/dmd/tree/master/compiler/test/dub_package
So something like this:
```json
{
"name": "lexer_test",
"dependencies": {
"dmd:frontend": "~>2.101.0"
}
}
```
source/lexer_test.d:
```d
module lexer_test.d;
void main()
{
import dmd.globals;
import dmd.lexer;
import dmd.tokens;
immutable expected = [
TOK.void_,
TOK.identifier,
TOK.leftParenthesis,
TOK.rightParenthesis,
TOK.leftCurly,
TOK.rightCurly
];
immutable sourceCode = "void test() {} // foobar";
scope lexer = new Lexer("test", sourceCode.ptr, 0,
sourceCode.length, 0, 0);
lexer.nextToken;
TOK[] result;
do
{
result ~= lexer.token.value;
} while (lexer.nextToken != TOK.endOfFile);
assert(result == expected);
}
```
And then just ``$ dub run``.
