UnguardedInsert

rascal-0.40.17

Synopsis

An insert occurs outside a visit expression.

Description

An insert statement may only occur in the action part of a pattern with action, more precisely in a case in a visit expression.

Remedies:

• Use an auxiliary variable and list or set operations to insert the value where you want.
• Place the insert statement inside a visit.

Examples

Here is an example of the use of insert to swap the arguments of red nodes:

Our favorite data type, colored trees:

rascal>data CTree = leaf(int n) | red(CTree left, CTree right) | green(CTree left, CTree right);
ok

An example tree:

rascal>CTree T = red(green(leaf(1), red(leaf(2), leaf(3))), red(leaf(4), leaf(5)));
CTree: red(
  green(
    leaf(1),
    red(
      leaf(2),
      leaf(3))),
  red(
    leaf(4),
    leaf(5)))

A visit to swap the arguments of red nodes:

rascal>visit(T){ case red(CTree l, CTree r): insert red(r,l); }
CTree: red(
  red(
    leaf(5),
    leaf(4)),
  green(
    leaf(1),
    red(
      leaf(3),
      leaf(2))))

An error occurs when insert is used outside a visit:

rascal>insert red(leaf(1), leaf(2));
|prompt:///|(0,29,<1,0>,<1,29>): Insert statement outside a visit statement
Advice: |https://www.rascal-mpl.org/docs/Rascal/Errors/CompileTimeErrors/UnguardedInsert|
ok