hackerbase/doc/utils.md

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.

Dictionary

(import util-dict-list)

This module implements a simple key/value dictionary using lists as backend. All operations are O(n) with respect to time.

(make-ldict [equality?/pairs [pairs]])

• equality?/pairs - procedure or list of pairs
• pairs - list of pairs

Creates a new ldict with configurable equality procedure, optionally populating it with initial data.

If only one argument is given, the procedure checks whether it is a list of equality procedure and acts accordingly.

(ldict? v)

• v - any value

Returns #t if given value is a ldict.

(ldict-empty? ld)

• ld - a ldict instance

Returns #t if given dictionary contains no keys.

(ldict-contains? ld k)

• ld - a ldict instance
• k - a key compatible with given ldict

Returns #t if given ld contains given key k.

(ldict-ref ld k [default])

• ld - a ldict instance
• k - a compatible key
• default - optional fallback value

Retrieves the value associated with given key in given dictionary. If the dictionary does not contain it and no default is given, an exception is raised. Otherwise the default value is returned in case of missing key.

(ldict-remove ld k)

• ld - a ldict instance
• k - a compatible key

Returns a new dictionary with the record under given key removed. If the dictionary does not contain the key k, an error is raised.

(ldict-set ld k v)

• ld - a ldict instance
• k - a compatible key
• v - a value to insert

Sets existing key k to the new value v or inserts it if it is not already present in the dictionary ld.

(ldict-keys ld)

• ld - a ldict instance

Returns the list of keys stored in given dictionary.

(ldict-map proc ld)

• proc - procedure accepting 1, 2 or 3 arguments
• ld - a ldict instance

Returns a new dictionary of the same type with all values processed by given procedure.

If it accepts one argument, only the value is passed to it. If it accepts two values, the key and the value is passed to it. And lastly if it accepts three arguments, the key, value and numeric index (starting from 0) are passed to it.

In all cases the value the procedure returns is taken as the new value for given key.

(ldict-filter pred? ld)

• pred? - predicate procedure
• ld -a ldict instance

Returns a new dictionary containing only key/value pairs matching the given predicate. The procedure pred? must accept two arguments - the key and the value.

(ldict-reduce init proc ld)

• init - initial accumulator value
• proc - accumulating procedure
• ld - a ldict instance

Performs a reduce operation on the pairs of given dictionary using init as initial accumulator. The accumulating procedure must accept three arguments: the value accumulated so far, the key and the value.

(ldict-equal? d1 d2 [equality?])

• d1 - a ldict instance
• d2 - a ldict instance
• equality? - optional equality? predicate for values

Returns #t if both dictionaries contain the same keys and their values are equal according to the provided equality? predicate which defaults to equal?.

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.