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(* Title: cases.ML
Author: Joshua Chen
Case reasoning.
*)
structure Case: sig
val rules: Proof.context -> thm list
val lookup_rule: Proof.context -> Termtab.key -> thm option
val register_rule: thm -> Context.generic -> Context.generic
end = struct
(* Context data *)
(*Stores elimination rules together with a list of the indexnames of the
variables each rule eliminates. Keyed by head of the type being eliminated.*)
structure Rules = Generic_Data (
type T = thm Termtab.table
val empty = Termtab.empty
val extend = I
val merge = Termtab.merge Thm.eq_thm_prop
)
val rules = map #2 o Termtab.dest o Rules.get o Context.Proof
fun lookup_rule ctxt = Termtab.lookup (Rules.get (Context.Proof ctxt))
fun register_rule rl =
let val hd = Term.head_of (Lib.type_of_typing (Thm.major_prem_of rl))
in Rules.map (Termtab.update (hd, rl)) end
(* [cases] attribute *)
val _ = Theory.setup (
Attrib.setup \<^binding>\<open>cases\<close>
(Scan.succeed (Thm.declaration_attribute register_rule))
""
#> Global_Theory.add_thms_dynamic (\<^binding>\<open>cases\<close>, rules o Context.proof_of)
)
end
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