Modula-2 Reloaded ⋄ Import Aggregators

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Import Aggregators

The following two approaches to import aggregation were discussed and rejected:

Re-Export by Default

Any module imported by a module might automatically be re-exported.

  • Advantages: No additional syntax required.
  • Disadvantages: Re-export cannot be turned off.

Implicit Re-Export

A definition part which imports one or more modules but exports no items on its own might be deemed to have the purpose of re-exporting all the imported modules ...

DEFINITION MODULE Collections;

IMPORT Stack, Queue, BinarySearchTree, Trie, HashTable, DynamicArray;

END Collections.
  • Advantages: No additional syntax required.
  • Disadvantages: Re-export will no longer work if the aggregate module is extended with declarations.

Importing the Aggregator

Importing Collections brings all re-exported modules into scope ...

MODULE UseCollections;

IMPORT Collections;

VAR
    stack : Stack;
...

stack := Stack.New(size, status);
...

END UseCollections.