' FB 1.05.0 Win64

Function checkNoSpaces(s As String) As Boolean
  For i As UInteger = 0 To Len(s) - 1
    If s[i] = 32 OrElse s[i] = 9 Then Return False  '' check for spaces or tabs
  Next
  Return True
End Function

Open "input.fasta" For Input As # 1

Dim As String ln, seq
Dim first As Boolean = True

While Not Eof(1)
  Line Input #1, ln
  If Left(ln, 1) = ">"  Then
    If Not first Then Print
    Print Mid(ln, 2); ": ";
    If first Then first = False
  ElseIf first Then
    Print: Print "Error : File does not begin with '>'";
    Exit While
  Else
    If checkNoSpaces(ln) Then
      Print ln;
    Else
      Print : Print "Error : Sequence contains space(s)";
      Exit While
    End If
  End If
Wend

Close #1

Print : Print
Print "Press any key to quit"
Sleep