nixpkgs/lib/strings.nix

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/* String manipulation functions. */
let lib = import ./default.nix;
inherit (builtins) length;
in
rec {
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inherit (builtins) stringLength substring head tail isString;
# Concatenate a list of strings.
concatStrings = lib.fold (x: y: x + y) "";
# Map a function over a list and concatenate the resulting strings.
concatMapStrings = f: list: concatStrings (map f list);
concatImapStrings = f: list: concatStrings (lib.imap f list);
# Place an element between each element of a list, e.g.,
# `intersperse "," ["a" "b" "c"]' returns ["a" "," "b" "," "c"].
intersperse = separator: list:
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if list == [] || length list == 1
then list
else [(head list) separator]
++ (intersperse separator (tail list));
# Concatenate a list of strings with a separator between each element, e.g.
# concatStringsSep " " ["foo" "bar" "xyzzy"] == "foo bar xyzzy"
concatStringsSep = separator: list:
concatStrings (intersperse separator list);
concatMapStringsSep = sep: f: list: concatStringsSep sep (map f list);
concatImapStringsSep = sep: f: list: concatStringsSep sep (lib.imap f list);
# Construct a Unix-style search path consisting of each `subDir"
# directory of the given list of packages. For example,
# `makeSearchPath "bin" ["x" "y" "z"]' returns "x/bin:y/bin:z/bin".
makeSearchPath = subDir: packages:
concatStringsSep ":" (map (path: path + "/" + subDir) packages);
# Construct a library search path (such as RPATH) containing the
# libraries for a set of packages, e.g. "${pkg1}/lib:${pkg2}/lib:...".
makeLibraryPath = makeSearchPath "lib";
# Idem for Perl search paths.
makePerlPath = makeSearchPath "lib/perl5/site_perl";
# Dependening on the boolean `cond', return either the given string
# or the empty string.
optionalString = cond: string: if cond then string else "";
# Determine whether a string has given prefix/suffix.
hasPrefix = pref: str:
eqStrings (substring 0 (stringLength pref) str) pref;
hasSuffix = suff: str:
let
lenStr = stringLength str;
lenSuff = stringLength suff;
in lenStr >= lenSuff &&
eqStrings (substring (lenStr - lenSuff) lenStr str) suff;
# Convert a string to a list of characters (i.e. singleton strings).
# For instance, "abc" becomes ["a" "b" "c"]. This allows you to,
# e.g., map a function over each character. However, note that this
# will likely be horribly inefficient; Nix is not a general purpose
# programming language. Complex string manipulations should, if
# appropriate, be done in a derivation.
stringToCharacters = s: let l = stringLength s; in
if l == 0
then []
else map (p: substring p 1 s) (lib.range 0 (l - 1));
# Manipulate a string charcater by character and replace them by strings
# before concatenating the results.
stringAsChars = f: s:
concatStrings (
map f (stringToCharacters s)
);
# same as vim escape function.
# Each character contained in list is prefixed by "\"
escape = list : string :
stringAsChars (c: if lib.elem c list then "\\${c}" else c) string;
# still ugly slow. But more correct now
# [] for zsh
escapeShellArg = lib.escape (stringToCharacters "\\ ';$`()|<>\t*[]");
# replace characters by their substitutes. This function is equivalent to
# the `tr' command except that one character can be replace by multiple
# ones. e.g.,
# replaceChars ["<" ">"] ["&lt;" "&gt;"] "<foo>" returns "&lt;foo&gt;".
replaceChars = del: new: s:
let
subst = c:
(lib.fold
(sub: res: if sub.fst == c then sub else res)
{fst = c; snd = c;} (lib.zipLists del new)
).snd;
in
stringAsChars subst s;
# Case conversion utilities
lowerChars = stringToCharacters "abcdefghijklmnopqrstuvwxyz";
upperChars = stringToCharacters "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
toLower = replaceChars upperChars lowerChars;
toUpper = replaceChars lowerChars upperChars;
# Appends string context from another string
addContextFrom = a: b: substring 0 0 a + b;
# Compares strings not requiring context equality
# Obviously, a workaround but works on all Nix versions
eqStrings = a: b: addContextFrom b a == addContextFrom a b;
# Cut a string with a separator and produces a list of strings which were
# separated by this separator. e.g.,
# `splitString "." "foo.bar.baz"' returns ["foo" "bar" "baz"].
splitString = _sep: _s:
let
sep = addContextFrom _s _sep;
s = addContextFrom _sep _s;
sepLen = stringLength sep;
sLen = stringLength s;
lastSearch = sLen - sepLen;
startWithSep = startAt:
substring startAt sepLen s == sep;
recurse = index: startAt:
let cutUntil = i: [(substring startAt (i - startAt) s)]; in
if index < lastSearch then
if startWithSep index then
let restartAt = index + sepLen; in
cutUntil index ++ recurse restartAt restartAt
else
recurse (index + 1) startAt
else
cutUntil sLen;
in
recurse 0 0;
# return the suffix of the second argument if the first argument match its
# prefix. e.g.,
# `removePrefix "foo." "foo.bar.baz"' returns "bar.baz".
removePrefix = pre: s:
let
preLen = stringLength pre;
sLen = stringLength s;
in
if hasPrefix pre s then
substring preLen (sLen - preLen) s
else
s;
removeSuffix = suf: s:
let
sufLen = stringLength suf;
sLen = stringLength s;
in
if sufLen <= sLen && eqStrings suf (substring (sLen - sufLen) sufLen s) then
substring 0 (sLen - sufLen) s
else
s;
# Return true iff string v1 denotes a version older than v2.
versionOlder = v1: v2: builtins.compareVersions v2 v1 == 1;
# Return true iff string v1 denotes a version equal to or newer than v2.
versionAtLeast = v1: v2: !versionOlder v1 v2;
# Get the version of the specified derivation, as specified in its
# name attribute.
getVersion = drv: (builtins.parseDrvName drv.name).version;
# Extract name with version from URL. Ask for separator which is
# supposed to start extension
nameFromURL = url: sep: let
components = splitString "/" url;
filename = lib.last components;
name = builtins.head (splitString sep filename);
in
assert ! eqStrings name filename;
name;
# Create an --{enable,disable}-<feat> string that can be passed to
# standard GNU Autoconf scripts.
enableFeature = enable: feat: "--${if enable then "enable" else "disable"}-${feat}";
}