Picat Tabling for Memoization 2

Question 1

Which Picat directive marks a predicate so that its results are automatically cached?

Accepted Answer

table

Answer

The `table` directive placed before a predicate definition enables automatic memoization in Picat.

Question 2

In Picat tabling, what happens when a tabled predicate is called with arguments it has already been called with?

Accepted Answer

The stored result is returned without re-executing the predicate body.

Answer

Tabling returns the cached result immediately, skipping redundant recomputation.

Question 3

What is the primary algorithmic benefit of tabling in recursive Picat programs?

Accepted Answer

It converts exponential-time recursion into polynomial-time computation by caching subproblem results.

Answer

Tabling eliminates redundant recursive calls, reducing exponential blowups typical in naive recursion.

Question 4

In a tabled Picat predicate with mode (+,+,-), what do the `-` signs indicate?

Accepted Answer

Output arguments whose values are stored in the table.

Answer

In tabling mode declarations, `-` denotes output (answer) arguments that the table records.

Question 5

Which classic dynamic programming problem is most naturally expressed using Picat tabling?

Accepted Answer

Fibonacci sequence computation

Answer

Fibonacci has heavily overlapping subproblems that tabling eliminates, making it a textbook tabling example.

Picat Practice Test