requires: {#Method. #ExtensibleSequence}.
provides: {#Condition. #Error. #Warning. #Restart. #Abort}.

"WARNING: This is all speculative and depends on bootstrap details which are
still forthcoming."

prototypes addDelegate: #conditions valued: Namespace clone.

conditions addSlot: #ErrorOutput valued: ConsoleOutput.
"The stream to which Error messages are sent. This should be StdErr and
overridable."

conditions addSlot: #Condition valued: Cloneable derive.
"A situation which is not handled in normal program logic, and may require
investigative or other special handling."
Condition addSlot: #handlers valued: ExtensibleSequence derive.
"The ordered group of handlers for the condition."

c@(Condition traits) defaultHandler
"Do nothing, and return nothing by default."
[Nil].

c@(Condition traits) isRestartAvailable
"Answer whether there is an available Restart for the Condition."
[
].

m@(Method traits) signal: c@(Condition traits)
"Signalling a Condition."
[
].

m@(Method traits) on: c@(Condition traits) do: block
"This is Smalltalk's main handler protocol carried over, usually for backing
out of a process."
[
].

m@(Method traits) handlersDo: block
"Applies the block to all of the active handlers, beginning with the most-
recently established."
"TODO: Method should be Activation in the dispatch."
[
].

conditions addSlot: #Restart valued: Condition derive.
"A Restart is a Condition which is signaled by another Condition for the
purpose of handling it."
Restart addSlot: #test valued: [| :condition | True].
"a Block that returns true if this handler applies to this condition. The default is a function that always returns true."

r@(Restart traits) appliesTo: c@(Condition traits)
"Answers whether the Restart applies to the Condition. The default is to use
the test slot."
"TODO: refactor the slot into this method?"
[
  r test value: c
].

r@(Restart traits) defaultHandler
[
  error: 'No handler for this Restart.'
].

conditions addSlot: #Abort valued: Restart derive.
"An Abort is a Restart which exits the computation, unwinding the stack."
Abort addSlot: #description valued: '<Abort>'.

m@(Method traits) abort
[
].

conditions addSlot: #Warning valued: Condition derive.
"Warnings are Conditions which should generate notifications, but do not need
to be raised for handling, i.e. no action needs to be taken."

m@(Method traits) warn: message
[
  Warning newWith: message
].

conditions addSlot: #SimpleWarning valued: Warning derive.
"A SimpleWarning is a Warning."

conditions addSlot: #StyleWarning valued: SimpleWarning derive.
"A StyleWarning is a Warning that certain conventions set up by the library
author have not been followed, which could lead to problems."

m@(Method traits) deprecated
[
  StyleWarning newWith: 'This method has been deprecated.'
].

conditions addSlot: #BreakPoint valued: SimpleWarning derive.
"A BreakPoint is a SimpleWarning raised when instrumenting code for
debugging from a particular place in the code."

m@(Method traits) break
[
  BreakPoint new
].

conditions addSlot: #SeriousCondition valued: Condition derive.
"A SeriousCondition is a Condition that requires handling, but is not a
semantic Error of the program. Rather, it's due to some incidental or
pragmatic consideration."

c@(SeriousCondition traits) defaultHandler
"Just raise a debugger if no handler is provided."
[
  c invokeDebugger
].

conditions addSlot: #Error valued: SeriousCondition derive.
"An Error is a SeriousCondition which involves some misstep in program logic,
and raises the need for handlers."

m@(Method traits) error: message
[
  Error newWith: message
].

m@(Method traits) methodNotFound
[
  Error newWith: 'This method was not found for the arguments.'
].

m@(Method traits) overrideThis
[
  Error newWith: 'The method was not defined by a child object as required.'
].