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

30 Jan 2011


      Maybe you want to remove Snowflake.o (or even *.o) and then try compiling it
again.

Regards,
Paul Liu

On Sun, Jan 30, 2011 at 4:11 PM, michael rice  wrote:
...
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
===============
[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
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Regards,
Paul Liu