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.

CSV

(import util-csv)

This module provides a very simple, incomplete and incorrect but fast CSV loader.

(csv-parse filename
	[#:separator #\;]
	[#:string-delimiter #\"])

• separator - cell separator in CSV file
• string-delimiter - for introducing strings possibly with separators

Parses given CSV file and returns list of lists of strings representing its contents.

(csv-split-header csv)

• csv - list of lists of strings

Splits given loaded CSV into two tables at the first empty row.

Dictionary

(import util-dict)

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-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.

IO

(import util-io)

Module implementing advanced I/O.

(read-lines/no-bom port)

• port - an input port

Reads lines using read-lines and if the first line contains UTF-8 BOM, removes it.

(get-process-output-lines cmd)

• cmd - a string with the command

Returns a list of strings representing all the lines produced by running the command given.

List

(import util-list)

This module implements basic list functionality which is common in most scheme implementations.

(filter pred? lst)

• pred? - procedure accepting any value and returning #t or #f
• lst - list to be filtered

Returns a list containing only elements matching given pred? predicate.

Parser

(import util-parser)

This module contains common functions for both configuration and member file parsers. All functions are UTF-8 aware.

(parser-preprocess-line line)

• line - a string with contents of one source line

If the input line contains the # character, the rest of the line (including this character) is removed.

Any leading and trailing space is removed.

Returns a string representing the preprocessed line.

(parser-parse-line line)

• line - preprocessed line (string)

If the line is empty, returns #f.

If the line contains only one token consisting of non-whitespace characters before the first whitespace character (there is no whitespace), returns a symbol created by interning the whole line.

When the line contains whitespace character(s), it returns a pair consisting of symbol created by interning the string of non-whitespace characters before the first whitespace character and the string with the rest of the line.

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-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.

String

(import util-string)

String manipulation functions which are used throughout other modules.

(string-repeat str rep)

• str - string to repeat
• rep - number of repeats

Returns a string created by repeating the string str exactly rep number of times.

(string-first+rest str)

• str - a string to split

Returns a pair of strings where the car of the pair is the first token in the str given and cdr is a string with the remainder with leading whitespace removed.

Tag

(import util-tag)

A unifying module for compound data structures tagging.

(make-tag name)

• name - unquoted symbol to base the tag on

Creates a unique and collision free symbol to identify compound data structures based on lists and pairs.

Time

(import util-time)

Compatibility module for the differences between chicken scheme version 5.2 and earlier and 5.3 and on.

(current-util-milliseconds)

Returns the number of milliseconds since process startup.

Under chicken scheme <5.3 it uses current-milliseconds and for chicken scheme >=5.3 it uses current-process-milliseconds.

Without this module compilation with current-milliseconds results in warnings on chicken scheme >=5.3 and compilation under chicken scheme <5.3 results in error with current-process-milliseconds.