author | wenzelm |
Sun, 07 Jan 2001 21:35:34 +0100 | |
changeset 10816 | 8b2eafed6183 |
parent 5184 | 9b8547a9496a |
child 12338 | de0f4a63baa5 |
permissions | -rw-r--r-- |
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(* Title: HOL/W0/Type.thy |
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ID: $Id$ |
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Author: Dieter Nazareth and Tobias Nipkow |
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Copyright 1995 TU Muenchen |
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MiniML-types and type substitutions. |
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*) |
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Type = Maybe + |
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(* new class for structures containing type variables *) |
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classes |
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type_struct < term |
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(* type expressions *) |
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datatype |
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typ = TVar nat | "->" typ typ (infixr 70) |
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(* type variable substitution *) |
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types |
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subst = nat => typ |
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arities |
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typ::type_struct |
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list::(type_struct)type_struct |
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fun::(term,type_struct)type_struct |
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(* substitutions *) |
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(* identity *) |
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constdefs |
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id_subst :: subst |
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"id_subst == (%n. TVar n)" |
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(* extension of substitution to type structures *) |
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consts |
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app_subst :: [subst, 'a::type_struct] => 'a::type_struct ("$") |
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primrec |
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app_subst_TVar "$ s (TVar n) = s n" |
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app_subst_Fun "$ s (t1 -> t2) = ($ s t1) -> ($ s t2)" |
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defs |
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app_subst_list "$ s == map ($ s)" |
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(* free_tv s: the type variables occuring freely in the type structure s *) |
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consts |
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free_tv :: ['a::type_struct] => nat set |
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primrec |
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"free_tv (TVar m) = {m}" |
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"free_tv (t1 -> t2) = (free_tv t1) Un (free_tv t2)" |
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primrec |
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"free_tv [] = {}" |
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"free_tv (x#l) = (free_tv x) Un (free_tv l)" |
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(* domain of a substitution *) |
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constdefs |
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dom :: subst => nat set |
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"dom s == {n. s n ~= TVar n}" |
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(* codomain of a substitutions: the introduced variables *) |
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constdefs |
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cod :: subst => nat set |
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"cod s == (UN m:dom s. free_tv (s m))" |
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defs |
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free_tv_subst "free_tv s == (dom s) Un (cod s)" |
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(* new_tv s n computes whether n is a new type variable w.r.t. a type |
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structure s, i.e. whether n is greater than any type variable |
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occuring in the type structure *) |
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constdefs |
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new_tv :: [nat,'a::type_struct] => bool |
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"new_tv n ts == ! m. m:free_tv ts --> m<n" |
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(* unification algorithm mgu *) |
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consts |
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mgu :: [typ,typ] => subst maybe |
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rules |
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mgu_eq "mgu t1 t2 = Ok u ==> $u t1 = $u t2" |
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mgu_mg "[| (mgu t1 t2) = Ok u; $s t1 = $s t2 |] ==> |
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? r. s = $r o u" |
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mgu_Ok "$s t1 = $s t2 ==> ? u. mgu t1 t2 = Ok u" |
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mgu_free "mgu t1 t2 = Ok u ==> free_tv u <= free_tv t1 Un free_tv t2" |
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end |
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