Conditions

TOM's mechanism of handling exceptional events and other such conditions is based on the conditions mechanism as provided by Common Lisp [gls].

The creation and issueing of conditions is handled through objects defined in the TOM unit (see section unit tom): Condition objects can be raised or signaled, and any object can be thrown.

Condition handling (in contrast to creation) is part of the language. For this purpose, TOM provides a few special expressions:

condition_expression:
          catch_expression
        | bind_expression
        | unwind_expression
        ;

• catch: to catch something that is being thrown
• bind: to define how conditions are to be handled
• unwind: to protect something against an undue throw

[Note: Currently, each Condition instance is associated with a ConditionClass instance; the instances of ConditionClass defining a single inheritance hierarchy of condition classes. Since real conditions need to be subclasses from Condition, to carry the extra state possibly needed, it seems a good idea to implement the condition class hierarchy within the TOM class hierarchy. End note.]

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