No Such Annotation
Synopsis
Annotation without a value.
Types
data RuntimeException = NoSuchAnnotation(str label);
Usage
import Exception; (only needed when NoSuchAnnotation is used in catch)
Description
An annotation can be associated with any node value (including any algebraic data type). This error is generated when the value of an annotation is requested but has not been defined.
Remedies:
- Ensure that the annotation value is properly initialized for all relevant parts of the node value.
- Use the isDefined and ifDefinedElse operators to check whether the annotation value is set and act accordingly.
- Catch the
NoSuchAnnotation yourself, see try catch.
Examples
rascal>data Fruit = apple(int n) | orange(int n);
ok
rascal>anno str Fruit @ quality;
ok
rascal>piece = orange(13);
Fruit: orange(13)
rascal>piece@quality;
|prompt:///|(0,5,<1,0>,<1,5>): NoSuchAnnotation("quality")
at $shell$(|prompt:///|(0,14,<1,0>,<1,14>))
ok
Use the unary postfix operator isDefined ? to check whether the quality annotation is set:
rascal>piece@quality?;
bool: false
Use the ternary operator ifDefinedElse ? to compute an alternative value when the quality annotation is not set:
rascal>piece@quality ? "no quality value";
str: "no quality value"
---
no quality value
---
We can also catch the NoSuchAnnotation error. First import the Rascal exceptions (which are also included in Prelude)
and IO:
rascal>import Exception;
ok
rascal>import IO;
ok
rascal>try piece@quality; catch NoSuchAnnotation(l): println("No such annotation: <l>");
No such annotation: quality
ok
Finally, we can just assign a value to the quality annotation:
rascal>piece@quality = "excellent";
Fruit: orange(13,quality="excellent")
rascal>piece@quality;
str: "excellent"
---
excellent
---
Pitfalls
WARNING: Using white space around the @ confuses the Rascal parser