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|
% strings.ml %
%-----------------------------------------------------------------------------%
% String functions. %
% Function to obtain a sub-string of a string s. The first i characters are %
% discarded, and the next l characters are taken as the sub-string. The %
% function fails if the string is not long enough to meet the requirements. %
let substr i l s =
% : (int -> int -> string -> string) %
letrec substr' i' l' sl sl' =
% : (int -> int -> string list -> string list -> string list) %
if (i' > 0)
then if (null sl)
then failwith `substr -- string too short`
else substr' (i'-1) l' (tl sl) sl'
else if (l' > 0)
then if (null sl)
then failwith `substr -- string too short`
else substr' i' (l'-1) (tl sl) ((hd sl).sl')
else rev sl'
in implode (substr' i l (explode s) []);;
% Function to find the number of characters in a string. %
let strlen s =
% : (string -> int) %
length (explode s);;
% Function to compute the length of the longest sequence of characters from %
% some set which begins a string. %
let num_of_leading_chars chars s =
% : (string list -> string -> int) %
letrec num_of_leading n chars sl =
% : (int -> string list -> string list -> int) %
if (null sl)
then n
else if (mem (hd sl) chars)
then num_of_leading (n+1) chars (tl sl)
else n
in num_of_leading 0 chars (explode s);;
% Function to remove characters from the beginning of a string. Characters %
% are removed until a character is encountered which does not occur in the %
% set of specified characters. %
let trim_leading_chars chars s =
% : (string list -> string -> string) %
letrec trim chars sl =
% : (string list -> string list -> string list) %
if (null sl)
then []
else if (mem (hd sl) chars)
then trim chars (tl sl)
else sl
in (implode o (trim chars) o explode) s;;
% Function to remove characters from the end of a string. Characters are %
% removed until a character is encountered which does not occur in the set %
% of specified characters. %
let trim_trailing_chars chars s =
% : (string list -> string -> string) %
letrec trim chars sl =
% : (string list -> string list -> string List) %
if (null sl)
then []
else let rest = trim chars (tl sl)
in if ((null rest) & (mem (hd sl) chars))
then []
else (hd sl).rest
in (implode o (trim chars) o explode) s;;
% Function to remove characters from the beginning and end of a string in %
% the manner of `trim_leading_chars' and `trim_trailing_chars'. %
let trim_enclosing_chars chars s =
% : (string list -> string -> string) %
trim_trailing_chars chars (trim_leading_chars chars s);;
% Function to test containment of string s2 in string s1. %
letrec string_contains s1 s2 =
% : (string -> string -> bool) %
if ((strlen s2) > (strlen s1))
then false
else if ((substr 0 (strlen s2) s1) = s2)
then true
else string_contains ((implode o tl o explode) s1) s2;;
% Function to test containment of string s within the strings sl. %
letrec strings_contain sl s =
% : (string list -> string -> bool) %
itlist (\x y. (string_contains x s) or y) sl false;;
% Function to make a string which is n copies of the string s. %
letrec string_copies s n =
% : (string -> int -> string) %
if (n < 1)
then ``
else s ^ (string_copies s (n - 1));;
%-----------------------------------------------------------------------------%
|
