Function evalLet

engine/transformer.go:43–60

evalLet evaluates a let transform. This consists of a number of let statements, each acting on a single row.

(
	head ast.Atom,
	transform ast.Transform,
	rows []ast.ConstSubstList,
	emit func(atom ast.Atom) bool)

// evalLet evaluates a let transform. This consists of a number of let statements,
// each acting on a single row.
func evalLet(
	head ast.Atom,
	transform ast.Transform,
	rows []ast.ConstSubstList,
	emit func(atom ast.Atom) bool) error {
	for _, init := range rows {
		subst := init
		for _, stmt := range transform.Statements {
			con, err := functional.EvalApplyFn(stmt.Fn, subst)
			if err != nil {
				return err
			}
			subst = subst.Extend(*stmt.Var, con)
		}
		emit(head.ApplySubst(subst).(ast.Atom))
	}
	return nil
}

type grouped struct {
	key    []ast.Constant