Haskell ã® "printf" デãƒã‚° - Inemuri nezumi diary(2007-05-11)_ Haskell ã® "printf" デãƒã‚° Stateモナドã¨ã‹IORefã¨ã‹ä½¿ã†ãƒ—ãƒã‚°ãƒ©ãƒ ã ã¨ã€å®Ÿè¡Œæ™‚ä¸ã«ä¸èº«ã‚’覗ããŸããªã‚‹ã€‚ã‚る人㌠unsafePerformIO 㧠print ã™ã‚‹ã¨ã‹è¨€ã†ã®ã§ã€ãã‚Œã¯ã¡ã‚‡ã£ã¨å¾…ã¦ã¨ã€‚Haskell ãŒãã®æ‰‹ã®ãƒ‡ãƒã‚°ãŒã—ã«ãã„ã®ã§ã€ä»–ã®è¨€èªžã«ç§»ã‚‹ã¨ã„ã†ã®ã¯ã€ã¡ã‚‡ã£ã¨ã ã‘å¾…ã£ã¦ã»ã—ã„。 Haskell ã«ã¯ Debug.Trace ã¨ã„ã†ãƒ¢ã‚¸ãƒ¥ãƒ¼ãƒ«ãŒã‚ã£ã¦ã€ãã®ä¸ã® trace :: String -> a -> a ã¯ã€IO ã‚’æ°—ã«ã›ãšã«æ–‡å—列を標準エラー出力ã«å‡ºã›ã‚‹ã®ã§ã™ã‚ˆã€‚ import "Debug.Trace" main = trace "Good morning" $ print "Hello, world" zsh% runghc TracingHello.hs 1> out.txt 2> err.txt zsh% cat out
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