Simple Parsec example, question I am learning Parsec and have been studying some great reference and tutorial sites I have found (much thanks to the authors), including: http://legacy.cs.uu.nl/daan/download/parsec/parsec.html#UserGuide http://legacy.cs.uu.nl/daan/download/parsec/parsec.html#ReferenceGuide http://book.realworldhaskell.org/read/using-parsec.html http://lstephen.wordpress.com/2007/06/19/first-go-with-parsec/ http://jonathan.tang.name/files/scheme_in_48/tutorial/overview.html http://www.defmacro.org/ramblings/lisp-in-haskell.html I'm having trouble coding a simple parser to count the number of lines in a text file. "lineCount" fails to compile; the compiler error text is below it. Any advice, code, etc. would be appreciated. For those using Gtk2Hs + Glade, I have included the glade file after the Haskell code, in case you want to try it. (You will need to remove the leading "> " and fix some lines that the email wrapped.) If you do wish to offer code, feel free to remove or rewrite: eol, textLines and lineCount entirely. I'm looking for the simplest way to code this. Thanks very much, -- Peter

-- A parsing demo, using: -- Haskell + Gtk2Hs + Glade (GtkBuilder) + Parsec module Main where

-- import Data.IORef import Graphics.UI.Gtk import Graphics.UI.Gtk.Builder import Graphics.UI.Gtk.Selectors.FileChooser -- import System.Cmd -- e.g., for invoking a shell cmd import System.Glib.GError import Text.ParserCombinators.Parsec

main :: IO () main = do initGUI

-- create builder; load UI file builder <- builderNew handleGError (\(GError dom code msg) -> fail msg) $ builderAddFromFile builder "demo.glade" -- Error message would look something like: -- app.exe: user error (Failed to open file 'app.glade': -- No such file or directory)

-- get widget handles (reduce boilerplate?) mainWindow <- builderGetObject builder castToWindow "mainWindow" pickFileButton <- builderGetObject builder castToFileChooserButton "pickFileButton" parseButton <- builderGetObject builder castToButton "parseButton" exitButton <- builderGetObject builder castToButton "exitButton"

-- signal handlers --

-- parse selected file onClicked parseButton $ do file <- fileChooserGetFilename pickFileButton

case file of Nothing -> do putStrLn "\nPlease first select a file." return () Just file -> do putStrLn $ "\nParsing file: " ++ show file result <- parseFromFile lineCount file case (result) of Left err -> print err Right x -> putStrLn $ "Line count = " ++ show x return ()

-- exit onDestroy mainWindow mainQuit onClicked exitButton mainQuit

-- go widgetShowAll mainWindow mainGUI

----------------- eol = char '\n'

-- from RWH; perhaps use in future: -- eol = try (string "\n\r") -- <|> try (string "\r\n") -- <|> string "\n" -- <|> string "\r" -- "end of line"

textLines = endBy eol

lineCount :: Parser Int lineCount = do xs <- textLines return (length xs)

-- demo.hs:72:3: -- Couldn't match expected type `GenParser Char () Int' -- against inferred type `GenParser Char st sep -> b' -- In a stmt of a 'do' expression: xs <- textLines -- In the expression: -- do { xs <- textLines; -- return (length xs) } -- In the definition of `lineCount': -- lineCount = do { xs <- textLines; -- return (length xs) }

-- demo.glade follows --

<?xml version="1.0"?> <interface> <requires lib="gtk+" version="2.16"/> <!-- interface-naming-policy project-wide --> <object class="GtkWindow" id="mainWindow"> <property name="visible">True</property> <property name="title" translatable="yes">demo v.8</property> <child> <object class="GtkVBox" id="vbox1"> <property name="visible">True</property> <property name="border_width">6</property> <property name="orientation">vertical</property> <property name="spacing">10</property> <child> <object class="GtkLabel" id="label1"> <property name="visible">True</property> <property name="tooltip_text" translatable="yes">You can hover over the buttons below for some information about them.

You can also resize this window, to make the buttons bigger. </property> <property name="label" translatable="yes">Demo: Haskell + Gtk2Hs + Glade (GtkBuilder) + Parsec </property> </object> <packing> <property name="position">0</property> </packing> </child> <child> <object class="GtkHBox" id="hbox1"> <property name="visible">True</property> <property name="spacing">5</property> <child> <object class="GtkFrame" id="pickFileframe"> <property name="visible">True</property> <property name="tooltip_text" translatable="yes">Use this File Chooser widget to select the file to parse. </property> <property name="label_xalign">0</property> <property name="shadow_type">none</property> <child> <object class="GtkAlignment" id="alignment1"> <property name="visible">True</property> <property name="left_padding">12</property> <child> <object class="GtkFileChooserButton" id="pickFileButton"> <property name="visible">True</property> <property name="title" translatable="yes">Select file</property> </object> </child> </object> </child> <child type="label"> <object class="GtkLabel" id="pickFileLabel"> <property name="visible">True</property> <property name="label" translatable="yes"><b>Select file to parse:</b></property> <property name="use_markup">True</property> </object> </child> </object> <packing> <property name="position">0</property> </packing> </child> <child> <object class="GtkButton" id="parseButton"> <property name="label" translatable="yes">P_arse</property> <property name="visible">True</property> <property name="can_focus">True</property> <property name="receives_default">True</property> <property name="tooltip_text" translatable="yes">Use this to parse the file you have selected.</property> <property name="use_underline">True</property> </object> <packing> <property name="position">1</property> </packing> </child> <child> <object class="GtkButton" id="exitButton"> <property name="label" translatable="yes">E_xit</property> <property name="visible">True</property> <property name="can_focus">True</property> <property name="receives_default">True</property> <property name="tooltip_text" translatable="yes">Exit this program and close both windows.</property> <property name="use_underline">True</property> </object> <packing> <property name="position">2</property> </packing> </child> </object> <packing> <property name="position">1</property> </packing> </child> </object> </child> </object> </interface>

-- end --