Name Errors/Dynamic/NoSuchAnnotation

Synopsis Annotation without a value.

Description An Rascal:Declarations/Annotation can be associated with any node value (including any Rascal:AlgebraicDataType). 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 Rascal:Boolean/isDefined and Rascal:Boolean/ifDefinedElse operators to check whether the annotation value is set and act accordingly.
• Catch the NoSuchAnnotation yourself, see Rascal:TryCatch.

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;
|stdin:///|(0,5,<1,0>,<1,5>): NoSuchAnnotation("quality")

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"

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"

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