Utility Modules
===============

To ensure there are no external dependencies (including chicken eggs),
these modules re-implement any basic procedures which are required for
any algorithms used. And some advanced yet generic functionality as
well.

The modules are listed in alphabetical order.

### Set (List)

    (import util-set-list)

This module implements linear-time set with custom comparator.

    (make-lset [comparator])

* ```comparator``` - comparison procedure, defaults to ```equal?```

Creates new lset with given comparator.

    (lset? v)

* ```v``` - any value

Returns ```#t``` if given value is a lset.

    (lset-empty? ls)

* ```ls``` - lset instance

Returns ```#t``` if given lset contains no elements.

    (lset-member? ls el)

* ```ls``` - lset instance
* ```el``` - element to check

Returns ```#t``` if given element ```el``` is contained in the lset
```ls``` using its equality comparator.

    (lset-count ls)

* ```ls``` - lset instance

Returns the number of elements in given lset.
  
    (lset-add ls [el ...])

* ```ls``` - lset instance
* ```el``` - element(s) to add

Adds given element(s) ```el``` to the lset instance ```ls``` returning
a new lset instance.

    (lset-remove ls el)

* ```ls``` - lset instance
* ```el``` - element to remove

If given lset instance ```ls``` contains the element ```el```
provided, it is removed and the new lset is returned. If the element
is not contained in ```ls```, it is returned intact.

    (list->lset lst [comparator])

* ```lst``` - list to convert
* ```comparator``` - equality comparison procedure, defaults to ```equal?```

Returns a new lset with the comparator provided containing all
elements in given list.

    (lset->list ls)

* ```ls``` - lset instance

Returns the list of elements in given lset.

    (lset-merge ls1 ls2)

* ```ls1``` - lset instance
* ```ls2``` - lset instance

Returns a new lset instance with all elements in both lset instances given.

    (lset-intersect ls1 ls2)

* ```ls1``` - lset instance
* ```ls2``` - lset instance

Returns a new lset instance containing elements present both in
```ls1``` and ```ls2```.

    (lset-subtract ls1 ls2)

Returns a new lset instance from ```ls1``` with all elements in
```ls2``` removed from it.

    (lset=? ls1 ls2)

* ```ls1``` - lset instance
* ```ls2``` - lset instance

Returns true if the sets contain exactly the same values.