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expr_set.go
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/
expr_set.go
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package rel
import (
"bytes"
"github.com/arr-ai/wbnf/parser"
"github.com/go-errors/errors"
)
// SetExpr returns the tuple or set with a single field replaced by an
// expression.
type SetExpr struct {
ExprScanner
elements []Expr
}
// NewSetExpr returns a new TupleExpr.
func NewSetExpr(scanner parser.Scanner, elements ...Expr) Expr {
values := make([]Value, len(elements))
for i, expr := range elements {
value, is := exprIsValue(expr)
if !is {
return &SetExpr{ExprScanner{scanner}, elements}
}
values[i] = value
}
return NewLiteralExpr(scanner, NewSet(values...))
}
// String returns a string representation of the expression.
func (e *SetExpr) String() string {
var b bytes.Buffer
b.WriteByte('{')
for i, expr := range e.elements {
if i > 0 {
b.WriteString(", ")
}
b.WriteString(expr.String())
}
b.WriteByte('}')
return b.String()
}
// Eval returns the subject
func (e *SetExpr) Eval(local Scope) (Value, error) {
values := make([]Value, 0, len(e.elements))
for _, expr := range e.elements {
value, err := EvalExpr(expr, local)
if err != nil {
return nil, wrapContext(err, e, local)
}
values = append(values, value)
}
return NewSet(values...), nil
}
// NewIntersectExpr evaluates a <&> b.
func NewIntersectExpr(scanner parser.Scanner, a, b Expr) Expr {
return newBinExpr(scanner, a, b, "<&>", "(%s <&> %s)",
func(a, b Value, _ Scope) (Value, error) {
if x, ok := a.(Set); ok {
if y, ok := b.(Set); ok {
return Intersect(x, y), nil
}
return nil, errors.Errorf("<&> rhs must be a Set, not %T", b)
}
return nil, errors.Errorf("<&> lhs must be a Set, not %T", a)
})
}