Q.PAT_ABBREV

STRUCTURE

SYNOPSIS

Introduces an abbreviation within the goal statement.

DESCRIPTION

When applied to the goal (asl, w), the tactic Q.PAT_ABBREV_TAC q parses the quotation q in the context of the goal, producing an equality term v = p. The tactic then uses HolKernel.gen_find_term to search for a sub-term of w that p matches against. If such a sub-term t is found then all occurrences of t (in asl and w) will be replaced by v and an assumption Abbrev(v = t) is added to the goal.

The trace variable "PAT_ABBREV_TAC: match var/const" controls whether or not trivial matches (with constants or variables) are allowed. By default trivial matches are permitted but when the trace variable is false the tactic will ignore trivial matches, which could result in failure.

FAILURE

PAT_ABBREV_TAC fails if q does not successfully parse as an equality or if no matching sub-term is found in the goal, or if the only matching sub-terms would bind pattern variables to variables that are bound in the goal.

EXAMPLE

If the current goal is

   ?- (n + 10) * y <= 42315

then applying the tactic Q.PAT_ABBREV_TAC `X = a * b: num` results in the goal

   Abbrev (X = (n + 10) * y)
      ?-
   X <= 42315

By default trivial matches are permitted. If the current goal is

   ?- y <= 42315

then Q.PAT_ABBREV_TAC `X = a: num` will give

   Abbrev (X = y)
      ?-
   X <= 42315

However, if this is not desirable then setting

Feedback.set_trace "PAT_ABBREV_TAC: match var/const" 0

and applying Q.PAT_ABBREV_TAC `X = a: num` will give

   Abbrev (X = 42315)
      ?-
   y <= X

If the current goal is

   ?- !x. x < 3

then applying Q.PAT_ABBREV_TAC `v = (a < b)` will result in a failure because the pattern’s variable a would have to bind the bound variable x in the goal.

SEEALSO

ABBREV_TAC, gen_find_term, MATCH_ABBREV_TAC