You are being caught by the fact that match_mp_tac thm can throw an exception
before the tactic is ever applied to a goal. In particular, if the theorem
passed to match_mp_tac is not an implication an exception is thrown
immediately.
You can fix this by handling that possible exception:
fun simple_apply thm = ACCEPT_TAC thm ORELSE (match_mp_tac thm handle
HOL_ERR _ => ALL_TAC)
This arguably a poor design for match_mp_tac, and should perhaps be changed.
Michael
On 23/8/17, 16:55, "Heiko Becker" <hbec...@mpi-sws.org> wrote:
Hello everyone,
while working on some custom tactics, I noticed some strange behavior
related to combining tactics with match_mp_tac and the ORELSE tactical:
I am trying to write a tactic takes a theorem and first tries out
whether it is already a proof of the current goal with ACCEPT_TAC.
If this does not succeed, the tactic should try matching the theorem
with match_mp_tac.
Here is what I have come up with:
fun simple_apply thm = (ACCEPT_TAC thm) ORELSE (match_mp_tac thm);
I have defined a test tactic, to see whether ACCEPT_TAC works as I
expect it to work:
fun dumb_apply thm = (ACCEPT_TAC thm) ORELSE (FAIL_TAC "Unreachable");
Strangely the simple_apply tactic does not work in cases, where the
dumb_apply tactic works:
val test_thm = Q.prove (
` !(n:num) (P:num -> bool).
P n ==>
P n`,
rpt gen_tac
DISCH_THEN ASSUME_TAC
qpat_x_assum `P n` (fn thm => simple_apply thm) (* Fails with "No
parse of quotation leads to success" *)
qpat_x_assum `P n` (fn thm => dumb_apply thm) (* Proves the goal *)
);
Can someone explain to me what I did wrong with the simple_apply tactic?
Thanks,
Heiko
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