Delphi – E2026 Constant expression expected

The Delphi compiler was expecting a constant expression here, but the expression it found was not constant.

program Produce;
const
  Message = 'Hello World!';
  WPosition = Pos('W', Message);
begin
end.

Even though its parameters are constants, the call to Pos is not a constant expression to the compiler, and it might theoretically be evaluated at compile time.

program Solve;
const
  Message = 'Hello World!';
  WPosition = 7;
begin
end.