minor performance tuning; directly try to read file instead of first checking its existence
(* Title: HOL/Proofs/ex/XML_Data.thy
Author: Makarius
Author: Stefan Berghofer
XML data representation of proof terms.
*)
theory XML_Data
imports "HOL-Examples.Drinker"
begin
subsection \<open>Export and re-import of global proof terms\<close>
ML \<open>
fun export_proof thy thm = thm
|> Proof_Syntax.standard_proof_of {full = true, expand_name = Thm.expand_name thm}
|> Proofterm.encode thy;
fun import_proof thy xml =
let
val prf = Proofterm.decode thy xml;
val (prf', _) = Proofterm.freeze_thaw_prf prf;
in Drule.export_without_context (Proof_Checker.thm_of_proof thy prf') end;
\<close>
subsection \<open>Examples\<close>
ML \<open>val thy1 = \<^theory>\<close>
lemma ex: "A \<longrightarrow> A" ..
ML_val \<open>
val xml = export_proof thy1 @{thm ex};
val thm = import_proof thy1 xml;
\<close>
ML_val \<open>
val xml = export_proof thy1 @{thm de_Morgan};
val thm = import_proof thy1 xml;
\<close>
ML_val \<open>
val xml = export_proof thy1 @{thm Drinker's_Principle};
val thm = import_proof thy1 xml;
\<close>
text \<open>Some fairly large proof:\<close>
ML_val \<open>
val xml = export_proof thy1 @{thm Int.times_int.abs_eq};
val thm = import_proof thy1 xml;
val xml_size = Bytes.size (YXML.bytes_of_body xml);
\<^assert> (xml_size > 10000000);
\<close>
end