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UndeclaredVariable

rascal-0.34.0

Synopsis​

Rascal can not find the definition of the name (identifier) used in an Expressions or Patterns.

Description​

A variable can only be used when it has been declared and initialized. This error is generated when this is not the case.

The error message is a bit of a misnomer, because it is produced when any identifier can not be found. That could be a name of a Function, of a Constructors, or a Pattern Variable, or a global Variable or a local Variable which can not be found in the current scope.

You can help Rascal find the name by:

  • Adding a new declaration of a Function, Constructors, a Variable or a Pattern Variable that has the given name.
  • Import or Extend a module that contains a definition of the given name.
  • Using a different name, or correcting a spelling error, such that Rascal can find the name in the current scope, or an imported or extended scope.

Examples​

Here is an example where an undeclared variables occurs in list splicing:

rascal>[1, *x, 3]
|prompt:///|(5,1,<1,5>,<1,6>): Undeclared variable: x
Advice: |https://www.rascal-mpl.org/docs/Rascal/Errors/CompileTimeErrors/UndeclaredVariable|
ok

The remedy is here:

rascal>x = [5];
list[int]: [5]
rascal>[1, *x, 3]
list[int]: [1,5,3]

Benefits​

  • Knowing this error statically means this can never happen at run-time if you do not get the error.
  • Variable references are never null in Rascal. In fact null is not a concept in Rascal at all.

Pitfalls​

  • Not only hard-to-find variable names produce UndeclaredVariable, also missing Functions and Constructors do.