Fine reasoning. Pure means incorruptible. It means that a pure result can be reused again and again -like the gold or silver- while an impure result must be re-created whenever it must be used. The metaphor is natural and I guess that the use of pure (rather than referential transparent) is informal, but as unavoidable as useful. By the way, there are deeper considerations here: To deal with pure values, like incorruptible stuff, like gold implies lower information costs and that´s one of the reasons why they are valuable.
In this sense, we can give a positive meaning to unsafePerformIO and change its name to "purify" or even "pasteurize" or "lyophilize" ;) 2013/8/7 Jerzy Karczmarczuk <jerzy.karczmarc...@unicaen.fr> > Richard A. O'Keefe : > > Haskell has **trained** my intuition to > see 'putStrLn "Hi"' as a pure value; it's not the thing itself that has > effects, > but its interpretation by an outer engine, just as my magnetic card key has by > itself no power to open doors, but the magnetic reader that looks at the > card_does_. > > I am the last here who would quarrel with Richard O'K., but I firmly > believe that such reasoning is a Pandora box. > > The King, the government, the Pope, etc. have no power, only the > interpretation of their decrees by "outer agents" _does_ things. > > Saying that the Justice of the country X is lousy is a harmful abuse. Our > Justice is good, only its interpretation by some incompetent traitors gave > rise to all these calamitous events. > > You see what I mean?... Are we going to switch now to the Mind-Body > dilemma? > > == > > BTW. Saying that "5" is a pure value means only that the whole of the > underlying system treats it as such. The object "5" couldn't care less. It > even doesn't know that in some programming language it is equivalent to an > action which puts it on the evaluation stack. > > That's why for me the "purity" (while teaching I try to avoid this word) > means simply that whatever you do with the object, it won't fire a "magic" > process. As Richard, I do not claim that this is "right", but it surely > facilitated my teaching of Haskell. My students have already more than > enough of my /philosophie de pacotille/... > > Jerzy Karczmarczuk > > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Alberto.
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