3_2 file error

program Laba_3_1;
{$APPTYPE CONSOLE}
uses
   SysUtils;
type
   TInputChoice = (TextFile, Console);
   TSet = set of Char;

const
   InstructionMessage
      = 'This program composes a set consisting of arithmetic operands and even digits';
   WayOfInputMessage = 'Where do you want to input data from? [F]ile or [C]onsole?';
   IncorrectInputFilePath = 'Incoorrect input file path, check if file exists and try again';
   IncorrectWayOfInputMessage = 'Incorrect way of input, choose [F]ile or [C]onsole';
   Mask = '-+*/02468';

function GetInputFilePath(): string;//проверка на пустоту
var
   Path: string;
begin
   Writeln('Enter input file path');
   Readln(Path);
   while not FileExists(Path) do
   begin
      Writeln(IncorrectInputFilePath);
      Readln(Path);
   end;

   GetInputFilePath := Path;
end;

function ChooseInputFromFileOrConsole(): TInputChoice;
var
   Choice: string;
begin
   Writeln(WayOfInputMessage);
   Readln(Choice);
   while (LowerCase(Choice) <> 'c') and (LowerCase(Choice) <> 'f') do
   begin
      Writeln(IncorrectWayOfInputMessage);
      Readln(Choice);
   end;

   if LowerCase(Choice) = 'f' then
      ChooseInputFromFileOrConsole := TextFile
   else
      ChooseInputFromFileOrConsole := Console;
end;

function GetSet(InputString: string): TSet;
var
   StringLength, i: Integer;
   Sequence: TSet;
begin
   Sequence := [];
   StringLength := Length(InputString);
   for i := 1 to StringLength do
      if (Pos(InputString[i], Mask) <> 0) and not(InputString[i] in Sequence) then
         Include(Sequence, InputString[i]);//Sequence := Sequence + [InputString[i]];

   GetSet := Sequence;
end;

procedure PrintSet(Sequence: TSet);
var
   i: Integer;
   OutputFile: TextFile;
begin
   if Sequence = [] then
      Writeln('Your sequence doesn''t contain any of assumed symbols')
   else
   begin
      Writeln('Composed set based on your sequence');
      for i := 0 to 255 do
         if Chr(i) in Sequence then
            Write(Chr(i), ' ');
   end;
end;

procedure Main();
var
   InputFilePath, InputString: string;
   Sequence: TSet;
begin
   Writeln(InstructionMessage);
   if ChooseInputFromFileOrConsole = TextFile then
      //Writeln('input from file');
      InputFilePath := GetInputFilePath()
   else
   begin
      Writeln('Input sequence of symbols');
      Readln(InputString);
      Sequence := GetSet(InputString);
      PrintSet(Sequence);
   end;

   Readln;
end;

begin
   Main();
end.