AuthorDr John A.R. Williams
StatusInitial Public Release
Copyright© 2010 J.A.R. Williams


DATA-FORMAT-VALIDATION is a library for Common Lisp providing a consistent regular interface for converting (and validating) external data (in the form of strings usually) into internal data types and for formatting internal data back into external presentable strings, all according to a conversion or type specification.

Table of Contents

Download and Installation

DATA-FORMAT-VALIDATION together with this documentation can be downloaded from the git repository at <git://> or from <>. The current release version is 0.1.6.

DATA-FORMAT-VALIDATION comes with a system definition for ASDF and is compiled and loaded in the usual way. It depends upon CL-PPCRE .

DATA-FORMAT-VALIDATION is made available under the terms of the GPL v3 license - see the file LICENSE.txt for details.


For questions, bug reports, feature requests, improvements, or patches please email <>.


generic function parse-input specification value &key &allow-other-keys => object

Validate and parse user input according to specification, returning the validated object. Throws an invalid-input condition if input is invalid. If specification is a list the first element specifies the actual validation method and the rest of the list are passed as keyword arguments to the specific method:

(parse-input '(integer :min 0) input)

will return the integer value from strin if it is >0, or signal and invalid-input error if not and:

(parse-input '(member :type integer :set (1 5 7)) input)

will return it only if it has a value in the set.

The use-value restart may be used to provide substitute value if the input is invalid.

generic function format-output specification value &key &allow-other-keys => string

Return a string representation of value formatted according to a specification. If specification is a list the first element specifies the actual validation method and the rest of the list are passed as keyword arguments to the specific method e.g.:

(format-output '(date :fmt :rfc2822) (get-universal-time))
>"Mon, 10 Jul 2006 15:43:45 +00"

generic function equivalent specification input reference &key &allow-other-keys => boolean
Return true if the input and reference values can be consider equivalent according to the specification. The default is to test using equal.
generic function parse-options spec options-list &optional allow-other-options => options
Parse an option list (alist of names and strings to be parsed) against a specification. The specification is a list of entries each of which lists the name, and optionally the type specification (to be used by parse-input) and the default value to be used if there is no entry in the options-list. The output is an alist of names and the parsed or default values. Options in options-list not in spec are not returned and will signal a correctable unknown-option error unless allow-other-options is true.
generic function parse-arguments spec argument-string &optional allow-spaces => arguments
Parse a string of whitespace delimited arguments according to spec. The specification is a list of entries each of which lists the name, and optionally the type specification (to be used by parse-input) and default values. The output is an alist of variable names and parsed values. If allow-spaces is true, last element can contain spaces (i.e. trailing spaces are not trimmed).
formatter function eng os arg &optional colon-p at-p d padchar exponentchar

Formatter which outputs its numerical argument arg in engineering format to stream os. It takes arguments d,padchar,exponentchar where d is the number of decimal places to display after the decimal point padchar is the character to pad the start of the number exponentchar is the character to use to display between radix and exponent It also takes the : modifier which will cause it to output the exponent as an SI units prefix rather than a number.

e.g. (format nil \" /eng/\" 35000) => \"35.00e+3\"

formatter function date os utime &optional colon-p at-p precision 6 timezone

Formatter which formats a universal time for output as a date and time


  • os: an output stream designator

  • arg: a universal time

  • colon-p: a generalised boolean (default false).

    If true use month and day names in date

  • at-p: a generalised boolean (default false) - if true print in yyyy-mm-dd

    (sortable) format rather than dd-mm-yyy

  • precision: what precision to print it to. 6 is to the second,

    7 includes timezone, a negative number counts backward.

  • timezone: an integer (default *timezone*).

    If nil no timezone used and time is in current timezone adjusted for daylight saving time.

e.g. (format nil \" /date/\" (get-universal-time)) => \"19-03-2009 08:30\""

function join-strings strings &optional (separator #\space) => string
Return a new string by joining together the list of strings, separating each string with a separator character or string
function split-string string &key count delimiter remove-empty-subseqs => list
Split string along whitespace as defined by the sequence delimiter. Whitespace which causes a split is elided from the result. The whole string will be split, unless max is provided, in which case the string will be split into this number of tokens at most, the last one containing the whole rest of the given string. If remove-empty-subseqs is true zero length entries are removed. This is similar to split-sequence however it only takes a string input and the delimiter may be a string.

Type Specifications

A type specification is an S-expression composed of a symbol specifying the particular conversion and a keyword argument list of qualifiers. Specific methods of parse-input and format-output are specialised on the conversion type symbol and take the remainder of the S-expression as an argument list. Adding your own conversions is simply a matter of providing appropriately specialised methods. The intended semantics are that the if the output from format-output is read back in using parse-input with thye same type specifications then an equivalent object should result.

Many conversions take the nil-allowed argument which convert an empty or all whitespace string to nil corresponding to a null input, otherwise an empty string is considered invalid input. Methods specialisations are provided for the following types:

boolean &key
Converts typical user boolean values (e.g. "TRUE", "Y", "0") into a boolean type. On output "TRUE" and "FALSE" are used.
bit-vector &key
Converts between a string of 0 and 1s and a bit vector.
date &key nil-allowed zone fmt Uses the parse-time library of

Jim Healy and Daniel Barlow to convert to internal universal time in specified timezone zone which to defaults to special variable *timezone* for output but to nil for parsing input. If zone is nil the time will be in the current timezone allowing for local daylight savings time - otherwise it is in the specified timezone, which will be written out.

fmt is a keyword specifying the output format to be used as follows.

A stand alone formatter of the same name is also provided.

:RFC2822 - output as per RFC2822 for internet messages :SHORT - output in a shorter format (same as :ISO) :TIME-ONLY - outputs time as hh:mm:ss :DATE-ONLY - outputs date as dd-mm-yyyy :ISO - output as per ISO 8602 (default)

dimensional-parameter &key padchar decimal-places tol

Converts between a string which includes units and normal scaling suffixes and a cons of the numerical value and the base units string. padchar and decimal-places are as per eng.

A dimensional comparator is equivalent if the numerical values and the units are equivalent.

eng &key units padchar decimal-places
Parse a number suffix with units. The standard engineering prefixes are assumed for the units (but with 'u' instead of 'µ'). The appropriatly scaled floating point value is returned and if the units. If units is a string then the input units suffix must match. On output the number will be scaled and the appropriate engineering prefix used. A general purpose formatter of the same name is also provided.
filename &key if-invalid replacement
Return a safe filename from a string path value. May return an error or replace invalid characters with the specified replacement letter (default '-');
headers `&key stream skip-blanks-p field-specifications

preserve-newlines-p termination-test if-no-specification` Parse or format internet message style headers. parse-input takes either a string or stream as the input value.

field-specifications is either an a-list by field name of giving the parse type specification to be applied recursively for that field or a function which returns the parse type specification and a present-p values in the usual way. if-no-specification specifies either a type specification to be used if the field is not found in field-specifications, :error for this case to be flagged as an error or :ignore to ignore fields without specifications. If defaults to nil i.e. value is passed through as a string without parsing.

skip-blanks-p will allow the parser to skip leading blank lines on the input. termination-test is a test function which of one argument (a string - a line) which should return true if the argument terminates the headers - default tests for a zero length line. If preserve-newlines-p is true then continuation lines will keep their newline characters, otherwise the newlines and first continuation character are removed.

format-output will write its output to stream if it is given, otherwise it will return a string containing the output headers.

integer &key min max nil-allowed radix format
Converts to an integer between min and max (inclusive, and if specified). radix specified the base (in the usual way). format specifies the format control string to be used for output.
list &key separator type min-length max-length
Return a list of objects delimited by the given separator string. Each member is recursively checked the nested type (another type specification). If specified min-length and max-length specify the required length bounds. The type specification may be a list of type specifications applied to each element in turn or a single type specification applied to all elements (note there is an ambiguity if you specify a list of one symbol - in this it is taken as a conversion for the first element only).
member &key type set test key
Recursively uses type to convert string to internal object which is then checked for membership of the list set using key and `test`(default is equal allowing for string tests).
nil &key
Return string unchanged.
number &key min max nil-allowed format radix tol

Converts to a general number between min and max (inclusive, and if specified). radix specified the base (in the usual way). format specifies the format control string to be used for output. The parse-number library of Matthew Danish is used to do the conversion.

tol is the tolerance to be used for equivalence testing - it can either be a multiplier applied to the reference value or a function of two arguments - the input and the reference value.

pathname &key must-exist wild-allowed nil-allowed
Convert input to a pathname. If wild-allowed is true then the pathname is allowed to be wild, otherwise if must-exist is true then the pathname must correspond to an existing file (checked using probe-file.
pathnames &key must-exist wild-allowed nil-allowed
Return a list of pathnames delimited by ':', each checked as for pathname
read &key multiplep type package
Uses the lisp reader with the current package set to package. type is a Common Lisp type against which the read object(s) is checked. If multiplep is true then read will be continually called until all characters are used up and the results are returned as a list. On output, if multiplep is true list of objects are separated by a space and written readably.
Convert between roman numerals (up to 4000) and an integer
string &key strip-return nil-allowed min-word-count max-word-count min-length max-length
Validates that the string is between min-length and max-length characters long (inclusive, and if specified) and the word count is between min-word-count and max-word-count. Whitespace is trimmed from the returned string, and if strip-return is specified the RETURN characters are stripped from the string (useful when handling input from http forms).
symbol &key nil-allowed package convert
Returns a symbol from the string interned into package (default is the keyword package). conversion is a function applied to the string before it is interned (default identity) which may for example be used to change case or map special characters.
time-period &key
A time period in hours, minutes and (optionally) seconds is converted into an integer number of seconds. ':' is used as the delimiter between fields.

Conditions and Restarts

is signalled if the input doesn't meet the type specification. It has readers invalid-format-value and invalid-format-reason.
restart may be invoked to specify a result to be used if invalid-input is signalled.
This restart is available for parse-options and parse-arguments and will result in a default specified value being used.


Matthew Danish for the parse-number library used and enclosed with this.

Daniel Barlow and Jim Healey for the parse-time library.