-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 10/2/10 19:59 , Russ Abbott wrote:
So what are the other options? I still like the idea of saying that [ ] is a function that takes a type as an argument and generates a value. (I believe
The best way to think abut this isn't really in terms of functions. The whole point of functional programming is referential transparency: in "let xs = [] ...", xs can be seen as a sort of "macro" which stands for its expansion. So you can use xs anywhere you would use [] and it will always behave as if you said [], including the polymorphism. Anywhere you use a binding, you are always able to substitute the bound expression. (This is why we need "magic" for IO. Conceptually, an IO "action" is a partial function which won't run until passed the baton; this same partial function can be substituted anywhere, but each substitution will be lazily evaluated when the baton reaches it (if in fact it ever does). The IO monad hides the baton-passing and makes sure it's done in legitimate ways. So in fact IO "actions" are entirely referentially transparent.) - -- brandon s. allbery [linux,solaris,freebsd,perl] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.10 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAkyn0ScACgkQIn7hlCsL25WtkACgy5bTsmQJATu9zSL29v3uX5Pg 3GoAn2QfkWhfNU3cbl0/ZKLjnS9VzZFm =I+TE -----END PGP SIGNATURE-----