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(* Title: CTT/ex/Typechecking.thy


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Author: Lawrence C Paulson, Cambridge University Computer Laboratory


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Copyright 1991 University of Cambridge


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*)


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header "Easy examples: type checking and type deduction"


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theory Typechecking


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imports CTT


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begin


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subsection {* Singlestep proofs: verifying that a type is wellformed *}


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schematic_lemma "?A type"

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apply (rule form_rls)


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done


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schematic_lemma "?A type"

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apply (rule form_rls)


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back


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apply (rule form_rls)


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apply (rule form_rls)


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done


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schematic_lemma "PROD z:?A . N + ?B(z) type"

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apply (rule form_rls)


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apply (rule form_rls)


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apply (rule form_rls)


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apply (rule form_rls)


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apply (rule form_rls)


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done


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subsection {* Multistep proofs: Type inference *}


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lemma "PROD w:N. N + N type"


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apply (tactic form_tac)


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done


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schematic_lemma "<0, succ(0)> : ?A"

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apply (tactic "intr_tac []")


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done


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schematic_lemma "PROD w:N . Eq(?A,w,w) type"

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apply (tactic "typechk_tac []")


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done


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schematic_lemma "PROD x:N . PROD y:N . Eq(?A,x,y) type"

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apply (tactic "typechk_tac []")


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done


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text "typechecking an application of fst"

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schematic_lemma "(lam u. split(u, %v w. v)) ` <0, succ(0)> : ?A"

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apply (tactic "typechk_tac []")


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done


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text "typechecking the predecessor function"

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schematic_lemma "lam n. rec(n, 0, %x y. x) : ?A"

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apply (tactic "typechk_tac []")


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done


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text "typechecking the addition function"

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schematic_lemma "lam n. lam m. rec(n, m, %x y. succ(y)) : ?A"

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apply (tactic "typechk_tac []")


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done


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(*Proofs involving arbitrary types.


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For concreteness, every type variable left over is forced to be N*)


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ML {* val N_tac = TRYALL (rtac (thm "NF")) *}


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schematic_lemma "lam w. <w,w> : ?A"

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apply (tactic "typechk_tac []")


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apply (tactic N_tac)


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done


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schematic_lemma "lam x. lam y. x : ?A"

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apply (tactic "typechk_tac []")


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apply (tactic N_tac)


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done


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text "typechecking fst (as a function object)"

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schematic_lemma "lam i. split(i, %j k. j) : ?A"

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apply (tactic "typechk_tac []")


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apply (tactic N_tac)


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done


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end
