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expr_safe_tail.go
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/
expr_safe_tail.go
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package rel
import (
"fmt"
"github.com/arr-ai/wbnf/parser"
)
type SafeTailCallback func(Value, Scope) (Value, error)
type SafeTailExpr struct {
ExprScanner
fallbackValue, base Expr
tailExprs []SafeTailCallback
}
func NewSafeTailExpr(scanner parser.Scanner, fallback, base Expr, tailExprs []SafeTailCallback) Expr {
if len(tailExprs) == 0 {
panic("exprs cannot be empty")
}
return &SafeTailExpr{ExprScanner{scanner}, fallback, base, tailExprs}
}
func (s *SafeTailExpr) Eval(local Scope) (value Value, err error) {
value, err = s.base.Eval(local)
if err != nil {
return nil, WrapContext(err, s, local)
}
for _, t := range s.tailExprs {
value, err = t(value, local)
if err != nil {
return nil, WrapContext(err, s, local)
}
if value == nil {
return s.fallbackValue.Eval(local)
}
}
return
}
func (s *SafeTailExpr) String() string {
//FIXME: printing not very descriptive
return fmt.Sprintf("%s...TODO...:%s", s.base.String(), s.fallbackValue.String())
}