This module contains a collection of functions for
obtaining lists of solutions to constraints.
These operations are useful to encapsulate
non-deterministic operations between I/O actions in
order to connects the worlds of logic and functional programming
and to avoid non-determinism failures on the I/O level.
In contrast the "old" concept of encapsulated search
(which could be applied to any subexpression in a computation),
the operations to encapsulate search in this module
are I/O actions in order to avoid some anomalities
in the old concept.
Datatypes:
SearchTree
Constructors:
SearchBranch
| Solutions
Functions:
getAllFailures
| getAllSolutions
| getOneSolution
| getOneValue
| getSearchTree
|
Summary of exported functions:
|
getAllSolutions :: (a -> Success) -> IO [a] 
|
|
Gets all solutions to a constraint (currently, via an incomplete
depth-first left-to-right strategy).
|
|
getOneSolution :: (a -> Success) -> IO (Maybe a)
|
|
Gets one solution to a constraint (currently, via an incomplete
left-to-right strategy).
|
|
getOneValue :: a -> IO (Maybe a)
|
|
Gets one value of an expression (currently, via an incomplete
left-to-right strategy).
|
|
getAllFailures :: a -> (a -> Success) -> IO [a]
|
|
Returns a list of values that do not satisfy a given constraint.
|
|
getSearchTree :: [a] -> (b -> Success) -> IO (SearchTree b a)
|
|
Computes a tree of solutions where the first argument determines
the branching level of the tree.
|
|
Prelude
A search tree for representing search structures.
Constructors:
-
SearchBranch
:: [(b,SearchTree a b)] -> SearchTree a b
-
Solutions
:: [a] -> SearchTree a b
getAllSolutions :: (a -> Success) -> IO [a]
Gets all solutions to a constraint (currently, via an incomplete
depth-first left-to-right strategy). Conceptually, all solutions
are computed on a copy of the constraint, i.e., the evaluation
of the constraint does not share any results. Moreover, this
evaluation suspends if the constraints contain unbound variables.
Similar to Prolog's findall.
getOneSolution :: (a -> Success) -> IO (Maybe a)
Gets one solution to a constraint (currently, via an incomplete
left-to-right strategy). Returns Nothing if the search space
is finitely failed.
getOneValue :: a -> IO (Maybe a)
Gets one value of an expression (currently, via an incomplete
left-to-right strategy). Returns Nothing if the search space
is finitely failed.
getAllFailures :: a -> (a -> Success) -> IO [a]
Returns a list of values that do not satisfy a given constraint.
Example call: (getAllFailures x c)
-
Parameters:
-
x
- an expression (a generator evaluable to various values)
-
c
- a constraint that should not be satisfied
-
Returns:
-
A list of all values of e such that (c e) is not provable
getSearchTree :: [a] -> (b -> Success) -> IO (SearchTree b a)
Computes a tree of solutions where the first argument determines
the branching level of the tree.
For each element in the list of the first argument,
the search tree contains a branch node with a child tree
for each value of this element. Moreover, evaluations of
elements in the branch list are shared within corresponding subtrees.
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(Version 0.4.1 of June 7, 2007) at Aug 28 15:25:25 2008