å˜åœ¨åž‹ (Existentially quantified data constructors) | tnomuraã®ãƒ–ãƒã‚°Haskell ã®å˜åœ¨åž‹ã¨ã„ã†ã®ã¯ä¸€ä½“ã©ã†ã„ã†æ„味ãªã®ã ã‚ã†ã‹ã€‚æ–‡å—列型や整数型ãªã‚‰æ„味ãŒã‚ã‹ã‚‹ã€‚ã—ã‹ã—ã€å˜åœ¨åž‹ã®å˜åœ¨ã¨ã„ã†è¨€è‘‰ã«ã©ã‚“ãªæ„味ãŒã“ã‚られã¦ã„ã‚‹ã®ã‹è¦‹å½“ã‚‚ã¤ã‹ãªã„。 探ã—回ã£ã¦ã„ãŸã‚‰ã€GHCã®ãƒžãƒ‹ãƒ¥ã‚¢ãƒ«ã® 7.4. Extensions to data types and type synonyms ã¨ã„ã†ãƒšãƒ¼ã‚¸ã‚’見ã¤ã‘ãŸã€‚ã“ã®ãƒšãƒ¼ã‚¸ã® 7.4.5. Existentially quantified data constructors ã«å˜åœ¨åž‹ã®èª¬æ˜ŽãŒæ›¸ã„ã¦ã‚ã£ãŸã€‚ã“れをèªã‚“ã ら疑å•ãŒæ°·è§£ã—ãŸã€‚ã©ã†ã‚‚å˜åœ¨åž‹ (Existetial type) ã®ã€Œå˜åœ¨ (Existential) ã€ã¨ã„ã†ã®ã¯ã€è¿°èªžè«–ç†å¦ã®å˜åœ¨é‡åŒ–åã®ã€Œå˜åœ¨ã€ã‚‰ã—ã„。ãŸã¨ãˆã°ã€ã€Œã‚る自然数 n ã«ã¤ã„ã¦ã€n * n ã¯ï¼’５ã§ã‚ã‚‹ã€ã¨ã„ã†å‘½é¡Œã‚’述語論ç†å¦ã®è¨˜å·ã§æ›¸ãã¨ä¸‹ã®ã‚ˆã†ã«ãªã‚‹ã€‚ ∃n (n ∈ N, n *
Motivation behind Phantom Types?
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