Re: [Haskell-cafe] Code from Haskell School of Expression hanging.

SimpleGraphics has a bunch of main programs: main0, main1, main2, main3, and main3book. I sequentially changed each to main and ran all five successfully. Then I did the same for Snowflake.lhs (see code below) which already had a single main function. Michael ============== [michael@localhost src]$ ghc --make Snowflake -main-is Snowflake Linking Snowflake ... /usr/lib/ghc-6.12.3/libHSrtsmain.a(Main.o): In function `main': (.text+0x10): undefined reference to `ZCMain_main_closure' /usr/lib/ghc-6.12.3/libHSrtsmain.a(Main.o): In function `main': (.text+0x18): undefined reference to `__stginit_ZCMain' collect2: ld returned 1 exit status [michael@localhost src]$ ============== This code was automatically extracted from a .lhs file that uses the following convention:   -- lines beginning with ">" are executable -- lines beginning with "<" are in the text,      but not necessarily executable -- lines beginning with "|" are also in the text,      but are often just expressions or code fragments.  

module Snowflake where import SOE   m = 81  :: Int -- multiple of 3 for triangle size x = 250 :: Int -- x and y coordinates of y = 250 :: Int --         center of snowflake colors = [ Magenta, Blue, Green, Red, Yellow ]   snowflake :: Window -> IO () snowflake w = do    drawTri w x y m 0 False -- draw first triangle w/flat top    flake   w x y m 0 True  -- begin recursion to complete job   flake :: Window -> Int -> Int -> Int -> Int -> Bool -> IO () flake w x y m c o = do    drawTri w x y m c o  -- draw second triangle    let c1 = (c+1)`mod`5 -- get next color    if (m<=3) then return ()  -- if too small, we're done       else do         flake w (x-2*m) (y-m) (m`div`3) c1 True  -- NW         flake w (x+2*m) (y-m) (m`div`3) c1 True  -- NE         flake w  x    (y+2*m) (m`div`3) c1 True  -- S         flake w (x-2*m) (y+m) (m`div`3) c1 False -- SW         flake w (x+2*m) (y+m) (m`div`3) c1 False -- SE         flake w  x    (y-2*m) (m`div`3) c1 False -- N   drawTri :: Window -> Int -> Int -> Int -> Int -> Bool -> IO () drawTri w x y m c o =    let d =  (3*m) `div` 2        ps = if o             then [(x,y-3*m),  (x-3*m,y+d), (x+3*m,y+d)] -- side at bottom             else [ (x,y+3*m), (x-3*m,y-d), (x+3*m,y-d)] -- side at top    in drawInWindow w         (withColor (colors !! c)            (polygon ps))   main    = runGraphics (      do w <- openWindow "Snowflake Fractal" (500,500)         drawInWindow w (withColor White           (polygon [(0,0),(499,0),(499,499),(0,499)]))         snowflake w         spaceClose w      )   spaceClose :: Window -> IO () spaceClose w    = do k <- getKey w         if k==' ' || k == '\x0'            then closeWindow w            else spaceClose w     --- On Sun, 1/30/11, Daniel Fischer wrote:

From: Daniel Fischer Subject: Re: [Haskell-cafe] Code from Haskell School of Expression hanging. To: haskell-cafe@haskell.org, "michael rice" Date: Sunday, January 30, 2011, 6:48 PM On Monday 31 January 2011 00:27:41, michael rice wrote:

And here's the same with GHC. It never gets to linking and creating an executable the way the GLFW sample program does.

Michael

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[michael@localhost ~]$ cd ./SOE/SOE/src [michael@localhost src]$ ghc --make SimpleGraphics.lhs [2 of 2] Compiling SimpleGraphics   ( SimpleGraphics.lhs, SimpleGraphics.o ) [michael@localhost src]$

The module name is not Main, so to get an executable, you have to tell ghc what the Main module is. Assuming SimpleGraphics.lhs contains a main function, $ ghc --make SimpleGraphics -main-is SimpleGraphics should do it. Cheers, Daniel