for S'Image use Func??
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From: J-P. Rosen on 17 May 2010 06:00 Niklas Holsti a �crit : >> And of course, you are welcome to have a look at my scanner in >> AdaControl ;-) > > I did, and I even compiled and tried it, but since your scanner ignores > and skips all line terminators (there is no "end of line" token kind), > its operation does not illuminate the question of the "wart". > Huh? There is an At_EoL boolean, even if it is not a full fledged token... -- --------------------------------------------------------- J-P. Rosen (rosen(a)adalog.fr) Visit Adalog's web site at http://www.adalog.fr
From: Niklas Holsti on 20 May 2010 05:31 J-P. Rosen wrote: > Niklas Holsti a �crit : >>> And of course, you are welcome to have a look at my scanner in >>> AdaControl ;-) >> I did, and I even compiled and tried it, but since your scanner ignores >> and skips all line terminators (there is no "end of line" token kind), >> its operation does not illuminate the question of the "wart". >> > Huh? There is an At_EoL boolean, even if it is not a full fledged token... Ah yes, there is an At_Eol variable in the package body, and a like-named component in the private type Scanner_State, but those are not accessible to clients of the scanner. I modified your package Framework.Language.Scanner, to provide a function that queries At_Eol, and made a test program that calls Start_Scan and then calls Next_Token repeatedly, until it returns the Eof (end of file) token. After each call of Next_Token the program prints out the line number of Standard_Input, Current_Token.Kind, and the value of At_Eol. In my experiments, the output is exactly the same for a file that consists of just one line of text, as for a file that consists of this one line of text followed by a null line. A client of your scanner thus cannot detect that the input file has a final empty line, which is the "wart" that has been discussed in this thread. I have found a work-around for the wart, so it is possible to use Text_IO to detect final empty lines. The following program counts the number of lines in the input file, and works even for empty files (/dev/null) and for files with final null lines. The trick is to use an extra call of Skip_Line to see if there is a final line terminator (for a null line) before the file terminator: with Ada.Text_IO; use Ada.Text_IO; procedure Count_Lines is Lines : Natural := 0; begin while not End_Of_File loop -- A non-null line at this point, or a null line -- that is not immediately followed by end of file. -- Process the line in some way; omitted here. Lines := Lines + 1; Skip_Line; end loop; -- Here we are at End_Of_File, but there may -- still be a line terminator for a null line -- immediately before the true end of the file. begin Skip_Line; -- Skip_Line raises End_Error if there is no line -- terminator before the end of the file. Lines := Lines + 1; exception when End_Error => null; end; Put_Line ("Lines:" & Natural'Image (Lines)); end Count_Lines; -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ .
From: Niklas Holsti on 21 May 2010 02:56
I am replying to my own post to show an even simpler solution to the "final empty line" problem. I guess this solution is what J-P. Rosen and others have suggested, earlier in this thread, but I have been too dense to understand. The "problem" is that the Text_IO functions End_Of_Line and End_Of_File give the same result when the input file is positioned at true end of file as when the file is positioned at a line terminator preceding the true end of file. This means that a reading loop of the form "while not End_Of_File loop <read a line> end loop" will ignore a final empty line. The simple solution is to use a loop that uses Get_Line (or Skip_Line) and terminates on the End_Error exception. This program reads and counts the lines in the input file and works for /dev/null (zero lines) as well as for files that end with empty lines: with Ada.Text_IO; use Ada.Text_IO; procedure Count_Lines is Lines : Natural := 0; begin loop declare The_Line : constant String := Get_Line; begin Lines := Lines + 1; end; end loop; exception when End_Error => Put_Line ("Lines:" & Natural'Image (Lines)); end Count_Lines; So, with apologies for any confusion about "warts" that I may have generated, I will now shut up. -- Niklas Holsti Tidorum Ltd niklas holsti tidorum fi . @ . |