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

[michael rice]

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 at 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 at 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 <daniel.is.fischer at googlemail.com> wrote:

From: Daniel Fischer <daniel.is.fischer at googlemail.com>
Subject: Re: [Haskell-cafe] Code from Haskell School of Expression hanging.
To: haskell-cafe at haskell.org, "michael rice" <nowgate at yahoo.com>
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 at localhost ~]$ cd ./SOE/SOE/src
> [michael at localhost src]$ ghc --make SimpleGraphics.lhs
> [2 of 2] Compiling SimpleGraphics   ( SimpleGraphics.lhs,
> SimpleGraphics.o ) [michael at 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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