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expr_dynlet.go
47 lines (41 loc) · 1.33 KB
/
expr_dynlet.go
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package rel
import (
"context"
"fmt"
"github.com/arr-ai/wbnf/parser"
)
// DynLetExpr implements "let bindings; expr", where bindings must evaluates to
// a tuple whose attributes are all dynamic names. These names will be bound
// dynamically for evaluation of expr.
type DynLetExpr struct {
ExprScanner
bindings Expr
expr Expr
}
// NewDynLetExpr returns a new DynLetExpr.
func NewDynLetExpr(scanner parser.Scanner, bindings, expr Expr) Expr {
return &DynLetExpr{ExprScanner: ExprScanner{scanner}, bindings: bindings, expr: expr}
}
// String returns a string representation of the expression.
func (e *DynLetExpr) String() string {
return fmt.Sprintf("(let %s; %s)", e.bindings, e.expr)
}
// Eval evaluates expr with the contents of bindings bound as dynamic variables.
func (e *DynLetExpr) Eval(ctx context.Context, local Scope) (Value, error) {
value, err := e.bindings.Eval(ctx, local)
if err != nil {
return nil, WrapContextErr(err, e, local)
}
t, is := value.(Tuple)
if !is {
return nil, fmt.Errorf(`bindings not a tuple in "let bindings; expr": %v`, value)
}
for e := t.Enumerator(); e.MoveNext(); {
name, value := e.Current()
if !isDynIdent(name) {
return nil, fmt.Errorf(`%q not a dynamic name in "let bindings; expr"`, name)
}
ctx = context.WithValue(ctx, DynIdent(name), value)
}
return e.expr.Eval(ctx, local)
}