我在Mac OS X版本10.9.4上使用Homebrew v0.9.5
当我运行命令:`brew install imagemagick时,发生了此错误.
$ brew install imagemagick
==> Installing dependencies for imagemagick: libpng, freetype
==> Installing imagemagick dependency: libpng
==> Downloading https://downloads.sf.net/project/machomebrew/Bottles/libpng-1.6.12.mavericks.bottle.tar.gz
curl: (7) Failed connect to downloads.sf.net:443; Operation timed out
Error: Failed to download resource "libpng"
Download failed: https://downloads.sf.net/project/machomebrew/Bottles/libpng-1.6.12.mavericks.bottle.tar.gz
Warning: Bottle installation failed: building from source.
==> Downloading https://downloads.sf.net/project/libpng/libpng16/1.6.12/libpng-1.6.12.tar.gz
curl: (7) Failed connect to downloads.sf.net:443; Operation timed out
Error: Failed to download resource "libpng"
Download failed: https://downloads.sf.net/project/libpng/libpng16/1.6.12/libpng-1.6.12.tar.gz
我添加了--disable-openmp选项,它也不顺利.
$ brew install imagemagick --disable-openmp
brew医生命令结果没问题.
$ …我已经检查了hoogle,http: //hackage.haskell.org/package/base-4.7.0.1/docs/Prelude.html#v:mapM
霍格尔说mapM_忽略了结果.
但我仍然不知道如何正确使用.
main = mapM_ (putStrLn.show) [1,2]
main = mapM (putStrLn.show) [1,2]
main = map (putStrLn.show) [1,2]