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All features
deferred class BACKTRACKING
Summary
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This class is intended to explore structures that matches the and/or graph of BACKTRACKING_NODE. The alternatives have a context that gotten and restored using the features 'get_context' and 'restore_context'.
See tutorial/backtracking for examples.
The instances of the BACKTRACKING children are typically used through lines like the following ones that enumerate the solutions: 
        from
           set_current_node(root)
           search_first
        until
           is_off
        loop
           ... -- do something
           search_next
        end
These features are declared to be bound to ANY but don't hesitate to change the type of the context to what your context is.
Direct parents
Inherit list: ABSTRACT_BACKTRACKING
Insert list: BACKTRACKING_GLOBALS
Known children
Inherit list: BACKTRACKING_REGULAR_EXPRESSION, XML_DTD_VALIDATOR
Class invariant
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Overview
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Features
{ANY}
internal
{}
Common client features
{ANY}
Control of the exploration
{ANY}
Internal
{}
Internal deferred
{}
Specific to sequences
{ABSTRACT_BACKTRACKING_SEQUENCE}
Specific to alternatives
{ABSTRACT_BACKTRACKING_ALTERNATIVE}
internal: allocation and collection
{}
{ANY}
the pools
{ANY}
set_current_node (node: BACKTRACKING_NODE)
effective procedure
{ANY}
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Sets the next node of the BACKTRACKING_NODE graph to evaluate.
ensure
push_and (node: BACKTRACKING_NODE)
effective procedure
{ANY}
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Pushes node in front of the continuation path.
require
  • node_not_void: node /= Void
push_and_list (list: BACKTRACKING_NODE_AND_LIST)
effective procedure
{ANY}
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Pushes list in front of the continuation path.
require
  • list_not_void: list /= Void
push_or (node: BACKTRACKING_NODE)
effective procedure
{ANY}
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Pushes node in front of the possible alternatives.
require
  • node_not_void: node /= Void
push_or_list (list: BACKTRACKING_NODE_OR_LIST)
effective procedure
{ANY}
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Pushes list in front of the possible alternatives.
require
  • list_not_void: list /= Void
current_node: BACKTRACKING_NODE
writable attribute
{}
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Current node of the BACKTRACKING_NODE graph to be evaluated.
evaluate_current_state
effective procedure
{}
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That feature is called to evaluate the current state
search_first
effective procedure
{ANY}
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Resets all and searches the first solution.
The current state must be set. It is the first state, the root of the search. When the feature returns, 'search_is_success' must be checked to know if a solution was found. When search_is_success=False, it means that there is no solution at all. Conversely, if search_is_success=True, then the first solution is found and 'search_next' can be called to get the next solution if it exists.
ensure
search_next
effective procedure
{ANY}
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Searches the next solution.
When the feature returns, 'search_is_success' must be checked to know if a solution was found. When search_is_success=False at the end, it means that there is no more solution. Conversely, if search_is_success=True, then a solution is found and 'search_next' can be called again to get the next solution.
require ensure
search_is_success: BOOLEAN
writable attribute
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True when search is successful
is_off: BOOLEAN
effective function
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True when search is finished
ensure
clear
effective procedure
{ANY}
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Clears the current state to nothing.
ensure
is_cleared: BOOLEAN
effective function
{ANY}
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True if no partial data remain in the current state
ensure
  • no_solution_when_cleared: Result implies is_off
push_sequence (sequence: ABSTRACT_BACKTRACKING_SEQUENCE)
effective procedure
{ANY}
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Pushes the sequence in front of the continuation path.
require
  • sequence_not_void: sequence /= Void
ensure
push_alternative (alternative: ABSTRACT_BACKTRACKING_ALTERNATIVE)
effective procedure
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Pushes the alternative before the continuation path.
require
  • alternative_not_void: alternative /= Void
ensure
continue
effective procedure
{ANY}
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Continues the exploration of the current path.
backtrack
effective procedure
{ANY}
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Stops the exploration of the current path and tries to explore the next alternative path.
push_cut_point
effective procedure
{ANY}
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Inserts a cut point into the continuation path.
The inserted cut point records the current top of the alternatives.
cut
effective procedure
{ANY}
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Removes the alternatives until the one recorded by the next cut point in the continuation path.
cut_all
effective procedure
{ANY}
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Cuts all alternatives.
stop_search_loop: BOOLEAN
writable attribute
{}
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True if at the end of a search.
This occurs if either a solution is found (and then search_is_success=True) or no solution is found (and then search_is_success=False). That feature should be modified only by continue and backtrack.
search
effective procedure
{}
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Common search loop to search_first and search_next
cut_until (alternative: ABSTRACT_BACKTRACKING_ALTERNATIVE)
effective procedure
{}
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Cut all alternatives until 'alternative'.
To cut an alternative is currently to remove it.
ensure
context_clear
deferred procedure
{}
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Clear any saved context.
Called by the features clear and search_first.
context_push
deferred procedure
{}
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Push the current context.
Called each time that an alternative begins.
context_restore
deferred procedure
{}
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Restore the context to the last saved one.
The saved context MUST remain available for future use. Called each time that a new alternative (of the previous alternative point) is starting.
context_restore_and_pop
deferred procedure
{}
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Restore the context to the last saved one and drop it.
The saved context MUST be removed. Called each time that the last alternative (of the previous alternative point) is starting. Should be similar to context_restore followed by context_cut.
context_cut
deferred procedure
{}
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Remove the last saved context.
Called by cut, cut_all or cut_until.
writable attribute
{ABSTRACT_BACKTRACKING_SEQUENCE}
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Stack of sequences represented by its top (can be Void)
current_continuation: ABSTRACT_BACKTRACKING_SEQUENCE
writable attribute
{ABSTRACT_BACKTRACKING_SEQUENCE}
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The current continuation path
pop_sequence
effective procedure
{ABSTRACT_BACKTRACKING_SEQUENCE}
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Removes the current sequence and replace it by the next sequence in the continuation path.
require
writable attribute
{ABSTRACT_BACKTRACKING_ALTERNATIVE}
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Stack of alternatives represented by its top (can be Void)
continue_alternative
effective procedure
{ABSTRACT_BACKTRACKING_ALTERNATIVE}
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Returns to the alternative on the top of the stack and put its saved continuation path as the current continuation path.
require ensure
pop_alternative
effective procedure
{ABSTRACT_BACKTRACKING_ALTERNATIVE}
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Returns to the alternative on the top of the stack and put its saved continuation path as the current continuation path.
Remove the alternative from the stack of alternatives. Same as continue_alternative but also removes the alternative.
require ensure
remove_top_sequence
effective procedure
{}
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Removes the top sequence.
require ensure
remove_top_alternative
effective procedure
{}
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Removes the top alternative.
require ensure
once function
{ANY}
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Bank of cut points
once function
{ANY}
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pool_of_sequence_list: BACKTRACKING_POOL_OF_SEQUENCE_LIST
once function
{ANY}
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pool_of_alternative: BACKTRACKING_POOL_OF_ALTERNATIVE
once function
{ANY}
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pool_of_alternative_list: BACKTRACKING_POOL_OF_ALTERNATIVE_LIST
once function
{ANY}
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