projection.pl -- Define the projection

This module redefines variables that are included in the SWISH result set.

To be done

- Removed variables should be removed from the template as well for efficiency reasons.

 projection(+Spec:list)

Specify the result variables. Using projection/1 at the start of a query specifies which variables are part of the result set, in what order they are displayed and, optionally, whether the results must be ordered on one or more variables or the solutions should be distinct. Each element of Spec is one of the following:

Var

Include Var in the result. Var must appear in the remainder of the body.

Var:Annotation

As Var, respecting Annotation. Valid annotations are below. Annotations may be abbreviated, e.g. asc, desc

ascending

Order solutions in ascending order.

descending

Order solutions is descending order

distinct

Remove duplicates wrt. this argument.

AnnA + AnnB

Multiple annotations

+ Var

Equivalent to Var:ascending

- Var

Equivalent to Var:descending

If ordering is specified for multiple variables, the result set is ordered starting with the left-most variable for which ordering is defined.

 preverse_vars(+Bindings, -ReservedBindings, ?Tail) is det[private]

Preserve some of the pseudo bindings that communicate additional information from the Pengine. May be extended by adding clauses to reserved_var/1.

 aggregation(+Projection:list, -Vars, +Goal0, -Goal) is semidet[private]

Determine the final projection variables as well as ordering and distinct wrapper from the projection argument.