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expr_tuple.go
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/
expr_tuple.go
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package rel
import (
"bytes"
"github.com/arr-ai/wbnf/parser"
"github.com/go-errors/errors"
)
// AttrExpr represents a single name:expr in a TupleExpr.
type AttrExpr struct {
ExprScanner
name string
expr Expr
}
// NewAttrExpr constructs a new AttrExpr from the given arguments.
func NewAttrExpr(scanner parser.Scanner, name string, expr Expr) (AttrExpr, error) {
isWildcard := false
if dot, ok := expr.(*DotExpr); ok {
if dot.Attr() == "*" {
isWildcard = true
expr = dot.Subject()
}
}
if isWildcard != (name == "*") {
return AttrExpr{}, errors.Errorf("Wildcard attr cannot have a name")
}
return AttrExpr{ExprScanner{scanner}, name, expr}, nil
}
func MustNewAttrExpr(scanner parser.Scanner, name string, expr Expr) AttrExpr {
attrExpr, err := NewAttrExpr(scanner, name, expr)
if err != nil {
panic(err)
}
return attrExpr
}
// NewWildcardExpr constructs a new wildcard AttrExpr.
func NewWildcardExpr(scanner parser.Scanner, lhs Expr) AttrExpr {
return AttrExpr{ExprScanner{scanner}, "*", lhs}
}
// IsWildcard returns true iff the AttrExpr is a wildcard expression.
func (e *AttrExpr) IsWildcard() bool {
return e.name == "*"
}
// Name returns the AttrExpr's name.
func (e *AttrExpr) Name() string {
return e.name
}
// Expr returns the AttrExpr's expr.
func (e *AttrExpr) Expr() Expr {
return e.expr
}
// Apply applies the AttrExpr to the Tuple.
func (e *AttrExpr) Apply(
local Scope, tuple Tuple,
) (Tuple, error) {
value, err := e.expr.Eval(local)
if err != nil {
return nil, err
}
if e.IsWildcard() {
if t, ok := value.(Tuple); ok {
for e := t.Enumerator(); e.MoveNext(); {
tuple = tuple.With(e.Current())
}
return tuple, nil
}
return nil, errors.Errorf(
"LHS of wildcard must be tuple, not %T", value)
}
tuple = tuple.With(e.name, value)
return tuple, nil
}
// TupleExpr returns a set from a slice of Exprs.
type TupleExpr struct {
ExprScanner
attrs []AttrExpr
attrMap map[string]Expr
}
// NewTupleExpr returns a new TupleExpr.
func NewTupleExpr(scanner parser.Scanner, attrs ...AttrExpr) Expr {
attrValues := make([]Attr, len(attrs))
for i, attr := range attrs {
if value, ok := attr.expr.(Value); ok {
attrValues[i] = Attr{attr.name, value}
} else {
attrMap := make(map[string]Expr, len(attrs))
for _, attr := range attrs {
attrMap[attr.name] = attr.expr
}
return &TupleExpr{ExprScanner{scanner}, attrs, attrMap}
}
}
return NewTuple(attrValues...)
}
// NewTupleExprFromMap returns a new TupleExpr from a map[string]Expr.
func NewTupleExprFromMap(scanner parser.Scanner, attrMap map[string]Expr) Expr {
attrValues := make([]Attr, len(attrMap))
i := 0
for name, expr := range attrMap {
if value, ok := expr.(Value); ok {
attrValues[i] = Attr{name, value}
i++
} else {
attrs := make([]AttrExpr, len(attrMap))
i := 0
for name, expr := range attrMap {
attrs[i] = AttrExpr{ExprScanner{scanner}, name, expr}
i++
}
return &TupleExpr{ExprScanner{scanner}, attrs, attrMap}
}
}
return NewTuple(attrValues...)
}
// Attrs returns a Tuple's attrs.
func (e *TupleExpr) Attrs() []AttrExpr {
return e.attrs
}
// String returns a string representation of the expression.
func (e *TupleExpr) String() string {
var b bytes.Buffer
b.WriteByte('(')
for i, attr := range e.attrs {
if i > 0 {
b.WriteString(", ")
}
if attr.IsWildcard() {
if attr.expr != DotIdent {
b.WriteString(attr.expr.String())
}
b.WriteString(".*")
} else {
b.WriteString(attr.name)
b.WriteString(": ")
b.WriteString(attr.expr.String())
}
}
b.WriteByte(')')
return b.String()
}
// Eval returns the subject
func (e *TupleExpr) Eval(local Scope) (Value, error) {
tuple := EmptyTuple
var err error
for _, attr := range e.attrs {
tuple, err = attr.Apply(local, tuple)
if err != nil {
return nil, wrapContext(err, e, local)
}
}
// TODO: Construct new tuple directly
return tuple.(*GenericTuple).Canonical(), nil
}
// Get returns the Expr for the given name or nil if not found.
func (e *TupleExpr) Get(name string) Expr {
return e.attrMap[name]
}