In Prolog, the built-in predicate `
findall/3` is used to gather all solutions to a query and collect them into a list. It allows you to find and collect multiple solutions to a goal or predicate into a structured format. Here's the use of the `
findall/3` predicate:
1. Gathering Solutions : * The primary purpose of `findall/3` is to collect all solutions to a query, even if there are multiple solutions or no solutions at all.
* It takes three arguments: a template, a goal, and a list variable to store the collected solutions.
* The template specifies the structure of the collected solutions.
* The goal represents the query for which you want to find solutions.
* `findall/3` evaluates the goal and collects all solutions, unifying them with the template and storing them in the list variable.
2. Generating Lists of Solutions : * By using `findall/3`, you can generate a list of all the solutions to a query, regardless of their multiplicity.
* If there are multiple solutions, they will be collected as separate elements in the resulting list.
* If there are no solutions, the resulting list will be empty.
3. Backtracking and Non-Determinism : * `findall/3` captures all solutions to a query at once, including alternative solutions obtained through backtracking.
* It collects all the solutions found during the entire search process and returns them in a list.
* This allows you to examine and analyze all the solutions, even if they are not unique or if the search involves non-deterministic behavior.
4. Result Aggregation : * `findall/3` is useful for aggregating results and gathering information from multiple solutions to perform further processing or analysis.
* It provides a convenient way to gather data and perform operations on the collected solutions as a whole.
Example usage :
?- findall(X, likes(X, pizza), PeopleWhoLikePizza).​
This query collects all individuals who like pizza, unifying them with the variable `X` and storing the solutions in the list `PeopleWhoLikePizza`.
