Picat Pattern Matching Rules 5

Question 1

In Picat, what is the difference between `==` and `=` when used in a rule body?

Accepted Answer

`==` tests strict equality without binding; `=` performs unification which may bind variables

Answer

`==` checks that two terms are identical without unifying them, while `=` attempts unification and may bind uninstantiated variables.

Question 2

A Picat rule written as `len([], Acc, Acc) => true.` is an example of what pattern technique?

Accepted Answer

Using an accumulator argument that matches when the base case (empty list) is reached

Answer

The pattern matches the empty list `[]` as the first argument and uses the same variable `Acc` twice to assert the accumulator equals the result at the base case.

Question 3

What does Picat do when a deterministic rule (`=>`) pattern matches but its body fails?

Accepted Answer

It throws an error and does NOT try other clauses

Answer

Once a deterministic (`=>`) rule's head matches, Picat commits; body failure propagates as an exception rather than triggering backtracking.

Question 4

Which Picat pattern would match a struct term `point(X, Y)` only when both coordinates are integers?

Accepted Answer

point(X, Y), integer(X), integer(Y) => ...

Answer

Picat uses guard conditions to further restrict matches; `integer(X)` and `integer(Y)` in the guard enforce the type constraint.

Question 5

In Picat, what is the outcome of `[1,2|T] = [1,2,3,4]`?

Accepted Answer

T = [3,4]

Answer

The pattern `[1,2|T]` matches a list starting with 1 and 2; T binds to the remaining tail `[3,4]`.

Picat Practice Test

Picat Practice Test

Picat Pattern Matching Rules 5