Located at lib/asserts.nix:19 in <nixpkgs>.

Print a trace message if pred is false.

Intended to be used to augment asserts with helpful error messages.

assert lib.asserts.assertMsg ("foo" == "bar") "foo is not bar, silly"
stderr> trace: foo is not bar, silly
stderr> assert failed

Located at lib/asserts.nix:36 in <nixpkgs>.

Specialized asserts.assertMsg for checking if val is one of the elements of xs. Useful for checking enums.

let sslLibrary = "bearssl";
in lib.asserts.assertOneOf "sslLibrary" sslLibrary [ "openssl" "libressl" ];
=> false
stderr> trace: sslLibrary must be one of "openssl", "libressl", but is: "bearssl"
        

Located at lib/attrsets.nix:24 in <nixpkgs>.

Return an attribute from within nested attribute sets.

let set = { a = { b = 3; }; };
in lib.attrsets.attrByPath [ "a" "b" ] 0 set
=> 3

lib.attrsets.attrByPath [ "a" "b" ] 0 {}
=> 0

Located at lib/attrsets.nix:42 in <nixpkgs>.

Determine if an attribute exists within a nested attribute set.

lib.attrsets.hasAttrByPath
  [ "a" "b" "c" "d" ]
  { a = { b = { c = { d = 123; }; }; }; }
=> true

Located at lib/attrsets.nix:57 in <nixpkgs>.

Create a new attribute set with value set at the nested attribute location specified in attrPath.

lib.attrsets.setAttrByPath [ "a" "b" ] 3
=> { a = { b = 3; }; }

Located at lib/attrsets.nix:76 in <nixpkgs>.

Like Section 5.1.2.1, “lib.attrset.attrByPath” except without a default, and it will throw if the value doesn't exist.

lib.attrsets.getAttrFromPath [ "a" "b" ] { a = { b = 3; }; }
=> 3

lib.attrsets.getAttrFromPath [ "x" "y" ] { }
=> error: cannot find attribute `x.y'

Located at lib/attrsets.nix:203 in <nixpkgs>.

Return the specified attributes from a set. All values must exist.

lib.attrsets.attrVals [ "a" "b" "c" ] { a = 1; b = 2; c = 3; }
=> [ 1 2 3 ]

lib.attrsets.attrVals [ "d" ] { }
error: attribute 'd' missing

Located at lib/attrsets.nix:213 in <nixpkgs>.

Get all the attribute values from an attribute set.

Provides a backwards-compatible interface of builtins.attrValues for Nix version older than 1.8.

lib.attrsets.attrValues { a = 1; b = 2; c = 3; }
=> [ 1 2 3 ]

Located at lib/attrsets.nix:232 in <nixpkgs>.

Collect each attribute named `attr' from the list of attribute sets, sets. Sets that don't contain the named attribute are ignored.

Provides a backwards-compatible interface of builtins.catAttrs for Nix version older than 1.9.

catAttrs "a" [{a = 1;} {b = 0;} {a = 2;}]
=> [ 1 2 ]
      

Located at lib/attrsets.nix:243 in <nixpkgs>.

Filter an attribute set by removing all attributes for which the given predicate return false.

filterAttrs (n: v: n == "foo") { foo = 1; bar = 2; }
=> { foo = 1; }

Located at lib/attrsets.nix:254 in <nixpkgs>.

Filter an attribute set recursively by removing all attributes for which the given predicate return false.

lib.attrsets.filterAttrsRecursive
  (n: v: v != null)
  {
    levelA = {
      example = "hi";
      levelB = {
        hello = "there";
        this-one-is-present = {
          this-is-excluded = null;
        };
      };
      this-one-is-also-excluded = null;
    };
    also-excluded = null;
  }
=> {
     levelA = {
       example = "hi";
       levelB = {
         hello = "there";
         this-one-is-present = { };
       };
     };
   }
     

Located at lib/attrsets.nix:273 in <nixpkgs>.

Apply fold function to values grouped by key.

lib.attrsets.foldAttrs
  (n: a: [n] ++ a) []
  [
    { a = 2; b = 7; }
    { a = 3; }
    { b = 6; }
  ]
=> { a = [ 2 3 ]; b = [ 7 6 ]; }

Located at lib/attrsets.nix:297 in <nixpkgs>.

Recursively collect sets that verify a given predicate named pred from the set attrs. The recursion stops when pred returns true.

lib.attrsets.collect isList { a = { b = ["b"]; }; c = [1]; }
=> [["b"] [1]]

collect (x: x ? outPath)
  { a = { outPath = "a/"; }; b = { outPath = "b/"; }; }
=> [{ outPath = "a/"; } { outPath = "b/"; }]

Located at lib/attrsets.nix:331 in <nixpkgs>.

Utility function that creates a {name, value} pair as expected by builtins.listToAttrs.

nameValuePair "some" 6
=> { name = "some"; value = 6; }

Located at lib/attrsets.nix:344 in <nixpkgs>.

Apply a function to each element in an attribute set, creating a new attribute set.

Provides a backwards-compatible interface of builtins.mapAttrs for Nix version older than 2.1.

lib.attrsets.mapAttrs
  (name: value: name + "-" + value)
  { x = "foo"; y = "bar"; }
=> { x = "x-foo"; y = "y-bar"; }

Located at lib/attrsets.nix:358 in <nixpkgs>.

Like mapAttrs, but allows the name of each attribute to be changed in addition to the value. The applied function should return both the new name and value as a nameValuePair.

lib.attrsets.mapAttrs' (name: value: lib.attrsets.nameValuePair ("foo_" + name) ("bar-" + value))
   { x = "a"; y = "b"; }
=> { foo_x = "bar-a"; foo_y = "bar-b"; }

    

Located at lib/attrsets.nix:374 in <nixpkgs>.

Call fn for each attribute in the given set and return the result in a list.

lib.attrsets.mapAttrsToList (name: value: "${name}=${value}")
   { x = "a"; y = "b"; }
=> [ "x=a" "y=b" ]

Located at lib/attrsets.nix:391 in <nixpkgs>.

Like mapAttrs, except that it recursively applies itself to attribute sets. Also, the first argument of the argument function is a list of the names of the containing attributes.

mapAttrsRecursive
  (path: value: concatStringsSep "-" (path ++ [value]))
  {
    n = {
      a = "A";
      m = {
        b = "B";
        c = "C";
      };
    };
    d = "D";
  }
=> {
     n = {
       a = "n-a-A";
       m = {
         b = "n-m-b-B";
         c = "n-m-c-C";
       };
     };
     d = "d-D";
   }
    

Located at lib/attrsets.nix:412 in <nixpkgs>.

Like mapAttrsRecursive, but it takes an additional predicate function that tells it whether to recursive into an attribute set. If it returns false, mapAttrsRecursiveCond does not recurse, but does apply the map function. It is returns true, it does recurse, and does not apply the map function.

lib.attrsets.mapAttrsRecursiveCond
  ({ recurse ? false, ... }: recurse)
  (name: value: builtins.toJSON value)
  {
    dorecur = {
      recurse = true;
      hello = "there";
    };
    dontrecur = {
      converted-to- = "json";
    };
  }
=> {
     dorecur = {
       hello = "\"there\"";
       recurse = "true";
     };
     dontrecur = "{\"converted-to\":\"json\"}";
   }
    

Located at lib/attrsets.nix:432 in <nixpkgs>.

Generate an attribute set by mapping a function over a list of attribute names.

lib.attrsets.genAttrs [ "foo" "bar" ] (name: "x_${name}")
=> { foo = "x_foo"; bar = "x_bar"; }
     

Located at lib/attrsets.nix:446 in <nixpkgs>.

Check whether the argument is a derivation. Any set with { type = "derivation"; } counts as a derivation.

lib.attrsets.isDerivation (import <nixpkgs> {}).ruby
=> true
     

lib.attrsets.isDerivation "foobar"
=> false
     

Located at lib/attrsets.nix:449 in <nixpkgs>.

Converts a store path to a fake derivation.

Located at lib/attrsets.nix:472 in <nixpkgs>.

Conditionally return an attribute set or an empty attribute set.

lib.attrsets.optionalAttrs true { my = "set"; }
=> { my = "set"; }
     

lib.attrsets.optionalAttrs false { my = "set"; }
=> { }
     

Located at lib/attrsets.nix:482 in <nixpkgs>.

Merge sets of attributes and use the function f to merge attribute values where the attribute name is in names.

lib.attrsets.zipAttrsWithNames
  [ "a" "b" ]
  (name: vals: "${name} ${toString (builtins.foldl' (a: b: a + b) 0 vals)}")
  [
    { a = 1; b = 1; c = 1; }
    { a = 10; }
    { b = 100; }
    { c = 1000; }
  ]
=> { a = "a 11"; b = "b 101"; }
     

Located at lib/attrsets.nix:497 in <nixpkgs>.

Merge sets of attributes and use the function f to merge attribute values. Similar to Section 5.1.2.22, “lib.attrsets.zipAttrsWithNames” where all key names are passed for names.

lib.attrsets.zipAttrsWith
  (name: vals: "${name} ${toString (builtins.foldl' (a: b: a + b) 0 vals)}")
  [
    { a = 1; b = 1; c = 1; }
    { a = 10; }
    { b = 100; }
    { c = 1000; }
  ]
=> { a = "a 11"; b = "b 101"; c = "c 1001"; }
     

Located at lib/attrsets.nix:505 in <nixpkgs>.

Merge sets of attributes and combine each attribute value in to a list. Similar to Section 5.1.2.23, “lib.attrsets.zipAttrsWith” where the merge function returns a list of all values.

lib.attrsets.zipAttrs
  [
    { a = 1; b = 1; c = 1; }
    { a = 10; }
    { b = 100; }
    { c = 1000; }
  ]
=> { a = [ 1 10 ]; b = [ 1 100 ]; c = [ 1 1000 ]; }
     

Located at lib/attrsets.nix:535 in <nixpkgs>.

Does the same as the update operator // except that attributes are merged until the given predicate is verified. The predicate should accept 3 arguments which are the path to reach the attribute, a part of the first attribute set and a part of the second attribute set. When the predicate is verified, the value of the first attribute set is replaced by the value of the second attribute set.

lib.attrsets.recursiveUpdateUntil (path: l: r: path == ["foo"])
  {
    # first attribute set
    foo.bar = 1;
    foo.baz = 2;
    bar = 3;
  }
  {
    #second attribute set
    foo.bar = 1;
    foo.quz = 2;
    baz = 4;
  }
=> {
  foo.bar = 1; # 'foo.*' from the second set
  foo.quz = 2; #
  bar = 3;     # 'bar' from the first set
  baz = 4;     # 'baz' from the second set
}
     

Located at lib/attrsets.nix:566 in <nixpkgs>.

A recursive variant of the update operator //. The recursion stops when one of the attribute values is not an attribute set, in which case the right hand side value takes precedence over the left hand side value.

recursiveUpdate
  {
    boot.loader.grub.enable = true;
    boot.loader.grub.device = "/dev/hda";
  }
  {
    boot.loader.grub.device = "";
  }
=> {
  boot.loader.grub.enable = true;
  boot.loader.grub.device = "";
}

Located at lib/attrsets.nix:636 in <nixpkgs>.

Make various Nix tools consider the contents of the resulting attribute set when looking for what to build, find, etc.

This function only affects a single attribute set; it does not apply itself recursively for nested attribute sets.

{ pkgs ? import <nixpkgs> {} }:
{
  myTools = pkgs.lib.recurseIntoAttrs {
    inherit (pkgs) hello figlet;
  };
}

Located at lib/attrsets.nix:316 in <nixpkgs>.

Return the cartesian product of attribute set value combinations.

cartesianProductOfSets { a = [ 1 2 ]; b = [ 10 20 ]; }
=> [
     { a = 1; b = 10; }
     { a = 1; b = 20; }
     { a = 2; b = 10; }
     { a = 2; b = 20; }
   ]

Concatenate a list of strings.

concatStrings ["foo" "bar"]
=> "foobar"

Located at lib/strings.nix:44 in <nixpkgs>.

Map a function over a list and concatenate the resulting strings.

concatMapStrings (x: "a" + x) ["foo" "bar"]
=> "afooabar"

Located at lib/strings.nix:54 in <nixpkgs>.

Like `concatMapStrings` except that the f functions also gets the position as a parameter.

concatImapStrings (pos: x: "${toString pos}-${x}") ["foo" "bar"]
=> "1-foo2-bar"

Located at lib/strings.nix:65 in <nixpkgs>.

Place an element between each element of a list

intersperse "/" ["usr" "local" "bin"]
=> ["usr" "/" "local" "/" "bin"].

Located at lib/strings.nix:75 in <nixpkgs>.

Concatenate a list of strings with a separator between each element

concatStringsSep "/" ["usr" "local" "bin"]
=> "usr/local/bin"

Located at lib/strings.nix:92 in <nixpkgs>.

Maps a function over a list of strings and then concatenates the result with the specified separator interspersed between elements.

concatMapStringsSep "-" (x: toUpper x)  ["foo" "bar" "baz"]
=> "FOO-BAR-BAZ"

Located at lib/strings.nix:105 in <nixpkgs>.

Same as `concatMapStringsSep`, but the mapping function additionally receives the position of its argument.

concatImapStringsSep "-" (pos: x: toString (x / pos)) [ 6 6 6 ]
=> "6-3-2"

Located at lib/strings.nix:122 in <nixpkgs>.

Construct a Unix-style, colon-separated search path consisting of the given `subDir` appended to each of the given paths.

makeSearchPath "bin" ["/root" "/usr" "/usr/local"]
=> "/root/bin:/usr/bin:/usr/local/bin"
makeSearchPath "bin" [""]
=> "/bin"

Located at lib/strings.nix:141 in <nixpkgs>.

Construct a Unix-style search path by appending the given `subDir` to the specified `output` of each of the packages. If no output by the given name is found, fallback to `.out` and then to the default.

makeSearchPathOutput "dev" "bin" [ pkgs.openssl pkgs.zlib ]
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r-dev/bin:/nix/store/wwh7mhwh269sfjkm6k5665b5kgp7jrk2-zlib-1.2.8/bin"

Located at lib/strings.nix:159 in <nixpkgs>.

Construct a library search path (such as RPATH) containing the libraries for a set of packages

makeLibraryPath [ "/usr" "/usr/local" ]
=> "/usr/lib:/usr/local/lib"
pkgs = import <nixpkgs> { }
makeLibraryPath [ pkgs.openssl pkgs.zlib ]
=> "/nix/store/9rz8gxhzf8sw4kf2j2f1grr49w8zx5vj-openssl-1.0.1r/lib:/nix/store/wwh7mhwh269sfjkm6k5665b5kgp7jrk2-zlib-1.2.8/lib"

Located at lib/strings.nix:177 in <nixpkgs>.

Construct a binary search path (such as $PATH) containing the binaries for a set of packages.

makeBinPath ["/root" "/usr" "/usr/local"]
=> "/root/bin:/usr/bin:/usr/local/bin"

Located at lib/strings.nix:186 in <nixpkgs>.

Normalize path, removing extranous /s

normalizePath "/a//b///c/"
=> "/a/b/c/"

Located at lib/strings.nix:196 in <nixpkgs>.

Depending on the boolean `cond', return either the given string or the empty string. Useful to concatenate against a bigger string.

optionalString true "some-string"
=> "some-string"
optionalString false "some-string"
=> ""

Located at lib/strings.nix:209 in <nixpkgs>.

Determine whether a string has given prefix.

hasPrefix "foo" "foobar"
=> true
hasPrefix "foo" "barfoo"
=> false

Located at lib/strings.nix:225 in <nixpkgs>.

Determine whether a string has given suffix.

hasSuffix "foo" "foobar"
=> false
hasSuffix "foo" "barfoo"
=> true

Located at lib/strings.nix:241 in <nixpkgs>.

Determine whether a string contains the given infix

hasInfix "bc" "abcd"
=> true
hasInfix "ab" "abcd"
=> true
hasInfix "cd" "abcd"
=> true
hasInfix "foo" "abcd"
=> false

Located at lib/strings.nix:266 in <nixpkgs>.

Convert a string to a list of characters (i.e. singleton strings). 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. Also note that Nix treats strings as a list of bytes and thus doesn't handle unicode.

stringToCharacters ""
=> [ ]
stringToCharacters "abc"
=> [ "a" "b" "c" ]
stringToCharacters "💩"
=> [ "�" "�" "�" "�" ]

Located at lib/strings.nix:287 in <nixpkgs>.

Manipulate a string character by character and replace them by strings before concatenating the results.

stringAsChars (x: if x == "a" then "i" else x) "nax"
=> "nix"

Located at lib/strings.nix:299 in <nixpkgs>.

Convert char to ascii value, must be in printable range

charToInt "A"
=> 65
charToInt "("
=> 40

Located at lib/strings.nix:318 in <nixpkgs>.

Escape occurrence of the elements of `list` in `string` by prefixing it with a backslash.

escape ["(" ")"] "(foo)"
=> "\\(foo\\)"

Located at lib/strings.nix:331 in <nixpkgs>.

Escape occurence of the element of `list` in `string` by converting to its ASCII value and prefixing it with \\x. Only works for printable ascii characters.

escapeC [" "] "foo bar"
=> "foo\\x20bar"

Located at lib/strings.nix:344 in <nixpkgs>.

Quote string to be used safely within the Bourne shell.

escapeShellArg "esc'ape\nme"
=> "'esc'\\''ape\nme'"

Located at lib/strings.nix:354 in <nixpkgs>.

Quote all arguments to be safely passed to the Bourne shell.

escapeShellArgs ["one" "two three" "four'five"]
=> "'one' 'two three' 'four'\\''five'"

Located at lib/strings.nix:364 in <nixpkgs>.

Test whether the given name is a valid POSIX shell variable name.

isValidPosixName "foo_bar000"
=> true
isValidPosixName "0-bad.jpg"
=> false

Located at lib/strings.nix:376 in <nixpkgs>.

Translate a Nix value into a shell variable declaration, with proper escaping.

The value can be a string (mapped to a regular variable), a list of strings (mapped to a Bash-style array) or an attribute set of strings (mapped to a Bash-style associative array). Note that "string" includes string-coercible values like paths or derivations.

Strings are translated into POSIX sh-compatible code; lists and attribute sets assume a shell that understands Bash syntax (e.g. Bash or ZSH).

''
${toShellVar "foo" "some string"}
[[ "$foo" == "some string" ]]
''

Located at lib/strings.nix:396 in <nixpkgs>.

Translate an attribute set into corresponding shell variable declarations using `toShellVar`.

let
foo = "value";
bar = foo;
in ''
${toShellVars { inherit foo bar; }}
[[ "$foo" == "$bar" ]]
''

Located at lib/strings.nix:424 in <nixpkgs>.

Turn a string into a Nix expression representing that string

escapeNixString "hello\${}\n"
=> "\"hello\\\${}\\n\""

Located at lib/strings.nix:434 in <nixpkgs>.

Turn a string into an exact regular expression

escapeRegex "[^a-z]*"
=> "\\[\\^a-z]\\*"

Located at lib/strings.nix:444 in <nixpkgs>.

Quotes a string if it can't be used as an identifier directly.

escapeNixIdentifier "hello"
=> "hello"
escapeNixIdentifier "0abc"
=> "\"0abc\""

Located at lib/strings.nix:456 in <nixpkgs>.

Escapes a string such that it is safe to include verbatim in an XML document.

escapeXML ''"test" 'test' < & >''
=> "&quot;test&quot; &apos;test&apos; &lt; &amp; &gt;"

Located at lib/strings.nix:470 in <nixpkgs>.

Converts an ASCII string to lower-case.

toLower "HOME"
=> "home"

Located at lib/strings.nix:500 in <nixpkgs>.

Converts an ASCII string to upper-case.

toUpper "home"
=> "HOME"

Located at lib/strings.nix:510 in <nixpkgs>.

Appends string context from another string. This is an implementation detail of Nix.

Strings in Nix carry an invisible `context` which is a list of strings representing store paths. If the string is later used in a derivation attribute, the derivation will properly populate the inputDrvs and inputSrcs.

pkgs = import <nixpkgs> { };
addContextFrom pkgs.coreutils "bar"
=> "bar"

Located at lib/strings.nix:525 in <nixpkgs>.

Cut a string with a separator and produces a list of strings which were separated by this separator.

splitString "." "foo.bar.baz"
=> [ "foo" "bar" "baz" ]
splitString "/" "/usr/local/bin"
=> [ "" "usr" "local" "bin" ]

Located at lib/strings.nix:536 in <nixpkgs>.

Return a string without the specified prefix, if the prefix matches.

removePrefix "foo." "foo.bar.baz"
=> "bar.baz"
removePrefix "xxx" "foo.bar.baz"
=> "foo.bar.baz"

Located at lib/strings.nix:554 in <nixpkgs>.

Return a string without the specified suffix, if the suffix matches.

removeSuffix "front" "homefront"
=> "home"
removeSuffix "xxx" "homefront"
=> "homefront"

Located at lib/strings.nix:578 in <nixpkgs>.

Return true if string v1 denotes a version older than v2.

versionOlder "1.1" "1.2"
=> true
versionOlder "1.1" "1.1"
=> false

Located at lib/strings.nix:600 in <nixpkgs>.

Return true if string v1 denotes a version equal to or newer than v2.

versionAtLeast "1.1" "1.0"
=> true
versionAtLeast "1.1" "1.1"
=> true
versionAtLeast "1.1" "1.2"
=> false

Located at lib/strings.nix:612 in <nixpkgs>.

This function takes an argument that's either a derivation or a derivation's "name" attribute and extracts the name part from that argument.

getName "youtube-dl-2016.01.01"
=> "youtube-dl"
getName pkgs.youtube-dl
=> "youtube-dl"

Located at lib/strings.nix:624 in <nixpkgs>.

This function takes an argument that's either a derivation or a derivation's "name" attribute and extracts the version part from that argument.

getVersion "youtube-dl-2016.01.01"
=> "2016.01.01"
getVersion pkgs.youtube-dl
=> "2016.01.01"

Located at lib/strings.nix:641 in <nixpkgs>.

Extract name with version from URL. Ask for separator which is supposed to start extension.

nameFromURL "https://nixos.org/releases/nix/nix-1.7/nix-1.7-x86_64-linux.tar.bz2" "-"
=> "nix"
nameFromURL "https://nixos.org/releases/nix/nix-1.7/nix-1.7-x86_64-linux.tar.bz2" "_"
=> "nix-1.7-x86"

Located at lib/strings.nix:657 in <nixpkgs>.

Create an --{enable,disable}-<feat> string that can be passed to standard GNU Autoconf scripts.

enableFeature true "shared"
=> "--enable-shared"
enableFeature false "shared"
=> "--disable-shared"

Located at lib/strings.nix:673 in <nixpkgs>.

Create an --{enable-<feat>=<value>,disable-<feat>} string that can be passed to standard GNU Autoconf scripts.

enableFeatureAs true "shared" "foo"
=> "--enable-shared=foo"
enableFeatureAs false "shared" (throw "ignored")
=> "--disable-shared"

Located at lib/strings.nix:686 in <nixpkgs>.

Create an --{with,without}-<feat> string that can be passed to standard GNU Autoconf scripts.

withFeature true "shared"
=> "--with-shared"
withFeature false "shared"
=> "--without-shared"

Located at lib/strings.nix:697 in <nixpkgs>.

Create an --{with-<feat>=<value>,without-<feat>} string that can be passed to standard GNU Autoconf scripts.

withFeatureAs true "shared" "foo"
=> "--with-shared=foo"
withFeatureAs false "shared" (throw "ignored")
=> "--without-shared"

Located at lib/strings.nix:710 in <nixpkgs>.

Create a fixed width string with additional prefix to match required width.

This function will fail if the input string is longer than the requested length.

fixedWidthString 5 "0" (toString 15)
=> "00015"

Located at lib/strings.nix:724 in <nixpkgs>.

Format a number adding leading zeroes up to fixed width.

fixedWidthNumber 5 15
=> "00015"

Located at lib/strings.nix:741 in <nixpkgs>.

Convert a float to a string, but emit a warning when precision is lost during the conversion

floatToString 0.000001
=> "0.000001"
floatToString 0.0000001
=> trace: warning: Imprecise conversion from float to string 0.000000
"0.000000"

Located at lib/strings.nix:753 in <nixpkgs>.

Check whether a value can be coerced to a string

Located at lib/strings.nix:760 in <nixpkgs>.

Check whether a value is a store path.

isStorePath "/nix/store/d945ibfx9x185xf04b890y4f9g3cbb63-python-2.7.11/bin/python"
=> false
isStorePath "/nix/store/d945ibfx9x185xf04b890y4f9g3cbb63-python-2.7.11"
=> true
isStorePath pkgs.python
=> true
isStorePath [] || isStorePath 42 || isStorePath {} || …
=> false

Located at lib/strings.nix:778 in <nixpkgs>.

Parse a string as an int. Does not support parsing of integers with preceding zero due to ambiguity between zero-padded and octal numbers. See toIntBase10.

toInt "1337"
=> 1337

toInt "-4"
=> -4

toInt " 123 "
=> 123

toInt "00024"
=> error: Ambiguity in interpretation of 00024 between octal and zero padded integer.

toInt "3.14"
=> error: floating point JSON numbers are not supported

Located at lib/strings.nix:808 in <nixpkgs>.

Parse a string as a base 10 int. This supports parsing of zero-padded integers.

toIntBase10 "1337"
=> 1337

toIntBase10 "-4"
=> -4

toIntBase10 " 123 "
=> 123

toIntBase10 "00024"
=> 24

toIntBase10 "3.14"
=> error: floating point JSON numbers are not supported

Located at lib/strings.nix:859 in <nixpkgs>.

Read a list of paths from `file`, relative to the `rootPath`. Lines beginning with `#` are treated as comments and ignored. Whitespace is significant.

NOTE: This function is not performant and should be avoided.

readPathsFromFile /prefix
./pkgs/development/libraries/qt-5/5.4/qtbase/series
=> [ "/prefix/dlopen-resolv.patch" "/prefix/tzdir.patch"
"/prefix/dlopen-libXcursor.patch" "/prefix/dlopen-openssl.patch"
"/prefix/dlopen-dbus.patch" "/prefix/xdg-config-dirs.patch"
"/prefix/nix-profiles-library-paths.patch"
"/prefix/compose-search-path.patch" ]

Located at lib/strings.nix:902 in <nixpkgs>.

Read the contents of a file removing the trailing \n

$ echo "1.0" > ./version

fileContents ./version
=> "1.0"

Located at lib/strings.nix:922 in <nixpkgs>.

Creates a valid derivation name from a potentially invalid one.

sanitizeDerivationName "../hello.bar # foo"
=> "-hello.bar-foo"
sanitizeDerivationName ""
=> "unknown"
sanitizeDerivationName pkgs.hello
=> "-nix-store-2g75chlbpxlrqn15zlby2dfh8hr9qwbk-hello-2.10"

Located at lib/strings.nix:937 in <nixpkgs>.

Computes the Levenshtein distance between two strings. Complexity O(n*m) where n and m are the lengths of the strings. Algorithm adjusted from https://stackoverflow.com/a/9750974/6605742

levenshtein "foo" "foo"
=> 0
levenshtein "book" "hook"
=> 1
levenshtein "hello" "Heyo"
=> 3

Located at lib/strings.nix:976 in <nixpkgs>.

Returns the length of the prefix common to both strings.

Located at lib/strings.nix:997 in <nixpkgs>.

Returns the length of the suffix common to both strings.

Located at lib/strings.nix:1005 in <nixpkgs>.

Returns whether the levenshtein distance between two strings is at most some value Complexity is O(min(n,m)) for k <= 2 and O(n*m) otherwise

levenshteinAtMost 0 "foo" "foo"
=> true
levenshteinAtMost 1 "foo" "boa"
=> false
levenshteinAtMost 2 "foo" "boa"
=> true
levenshteinAtMost 2 "This is a sentence" "this is a sentense."
=> false
levenshteinAtMost 3 "This is a sentence" "this is a sentense."
=> true

Located at lib/strings.nix:1029 in <nixpkgs>.

The identity function For when you need a function that does “nothing”.

Located at lib/trivial.nix:12 in <nixpkgs>.

The constant function

Ignores the second argument. If called with only one argument, constructs a function that always returns a static value.

let f = const 5; in f 10
=> 5

Located at lib/trivial.nix:26 in <nixpkgs>.

Pipes a value through a list of functions, left to right.

pipe 2 [
(x: x + 2)  # 2 + 2 = 4
(x: x * 2)  # 4 * 2 = 8
]
=> 8

# ideal to do text transformations
pipe [ "a/b" "a/c" ] [

# create the cp command
(map (file: ''cp "${src}/${file}" $out\n''))

# concatenate all commands into one string
lib.concatStrings

# make that string into a nix derivation
(pkgs.runCommand "copy-to-out" {})

]
=> <drv which copies all files to $out>

The output type of each function has to be the input type
of the next function, and the last function returns the
final value.

Located at lib/trivial.nix:61 in <nixpkgs>.

Concatenate two lists

concat [ 1 2 ] [ 3 4 ]
=> [ 1 2 3 4 ]

Located at lib/trivial.nix:80 in <nixpkgs>.

boolean “or”

Located at lib/trivial.nix:83 in <nixpkgs>.

boolean “and”

Located at lib/trivial.nix:86 in <nixpkgs>.

bitwise “and”

Located at lib/trivial.nix:89 in <nixpkgs>.

bitwise “or”

Located at lib/trivial.nix:94 in <nixpkgs>.

bitwise “xor”

Located at lib/trivial.nix:99 in <nixpkgs>.

bitwise “not”

Located at lib/trivial.nix:104 in <nixpkgs>.

Convert a boolean to a string.

This function uses the strings "true" and "false" to represent boolean values. Calling `toString` on a bool instead returns "1" and "" (sic!).

Located at lib/trivial.nix:114 in <nixpkgs>.

Merge two attribute sets shallowly, right side trumps left

mergeAttrs :: attrs -> attrs -> attrs

mergeAttrs { a = 1; b = 2; } { b = 3; c = 4; }
=> { a = 1; b = 3; c = 4; }

Located at lib/trivial.nix:124 in <nixpkgs>.

Flip the order of the arguments of a binary function.

flip concat [1] [2]
=> [ 2 1 ]

Located at lib/trivial.nix:138 in <nixpkgs>.

Apply function if the supplied argument is non-null.

mapNullable (x: x+1) null
=> null
mapNullable (x: x+1) 22
=> 23

Located at lib/trivial.nix:148 in <nixpkgs>.

Returns the current full nixpkgs version number.

Located at lib/trivial.nix:164 in <nixpkgs>.

Returns the current nixpkgs release number as string.

Located at lib/trivial.nix:167 in <nixpkgs>.

The latest release that is supported, at the time of release branch-off, if applicable.

Ideally, out-of-tree modules should be able to evaluate cleanly with all supported Nixpkgs versions (master, release and old release until EOL). So if possible, deprecation warnings should take effect only when all out-of-tree expressions/libs/modules can upgrade to the new way without losing support for supported Nixpkgs versions.

This release number allows deprecation warnings to be implemented such that they take effect as soon as the oldest release reaches end of life.

Located at lib/trivial.nix:180 in <nixpkgs>.

Whether a feature is supported in all supported releases (at the time of release branch-off, if applicable). See `oldestSupportedRelease`.

Located at lib/trivial.nix:186 in <nixpkgs>.

Returns the current nixpkgs release code name.

On each release the first letter is bumped and a new animal is chosen starting with that new letter.

Located at lib/trivial.nix:198 in <nixpkgs>.

Returns the current nixpkgs version suffix as string.

Located at lib/trivial.nix:201 in <nixpkgs>.

Attempts to return the the current revision of nixpkgs and returns the supplied default value otherwise.

Located at lib/trivial.nix:212 in <nixpkgs>.

Determine whether the function is being called from inside a Nix shell.

Located at lib/trivial.nix:230 in <nixpkgs>.

Determine whether the function is being called from inside pure-eval mode by seeing whether `builtins` contains `currentSystem`. If not, we must be in pure-eval mode.

Located at lib/trivial.nix:238 in <nixpkgs>.

Return minimum of two numbers.

Located at lib/trivial.nix:243 in <nixpkgs>.

Return maximum of two numbers.

Located at lib/trivial.nix:246 in <nixpkgs>.

Integer modulus

mod 11 10
=> 1
mod 1 10
=> 1

Located at lib/trivial.nix:256 in <nixpkgs>.

C-style comparisons

a < b, compare a b => -1 a == b, compare a b => 0 a > b, compare a b => 1

Located at lib/trivial.nix:267 in <nixpkgs>.

Split type into two subtypes by predicate `p`, take all elements of the first subtype to be less than all the elements of the second subtype, compare elements of a single subtype with `yes` and `no` respectively.

let cmp = splitByAndCompare (hasPrefix "foo") compare compare; in

cmp "a" "z" => -1
cmp "fooa" "fooz" => -1

cmp "f" "a" => 1
cmp "fooa" "a" => -1
# while
compare "fooa" "a" => 1

Located at lib/trivial.nix:292 in <nixpkgs>.

Reads a JSON file.

Type :: path -> any

Located at lib/trivial.nix:312 in <nixpkgs>.

Reads a TOML file.

Type :: path -> any

Located at lib/trivial.nix:319 in <nixpkgs>.

Print a warning before returning the second argument. This function behaves like `builtins.trace`, but requires a string message and formats it as a warning, including the `warning: ` prefix.

To get a call stack trace and abort evaluation, set the environment variable `NIX_ABORT_ON_WARN=true` and set the Nix options `--option pure-eval false --show-trace`

Located at lib/trivial.nix:347 in <nixpkgs>.

Like warn, but only warn when the first argument is `true`.

Located at lib/trivial.nix:357 in <nixpkgs>.

Like warnIf, but negated (warn if the first argument is `false`).

Located at lib/trivial.nix:364 in <nixpkgs>.

Like the `assert b; e` expression, but with a custom error message and without the semicolon.

If true, return the identity function, `r: r`.

If false, throw the error message.

Calls can be juxtaposed using function application, as `(r: r) a = a`, so `(r: r) (r: r) a = a`, and so forth.

throwIfNot (lib.isList overlays) "The overlays argument to nixpkgs must be a list."
lib.foldr (x: throwIfNot (lib.isFunction x) "All overlays passed to nixpkgs must be functions.") (r: r) overlays
pkgs

Located at lib/trivial.nix:386 in <nixpkgs>.

Like throwIfNot, but negated (throw if the first argument is `true`).

Located at lib/trivial.nix:393 in <nixpkgs>.

Check if the elements in a list are valid values from a enum, returning the identity function, or throwing an error message otherwise.

let colorVariants = ["bright" "dark" "black"]
in checkListOfEnum "color variants" [ "standard" "light" "dark" ] colorVariants;
=>
error: color variants: bright, black unexpected; valid ones: standard, light, dark

Located at lib/trivial.nix:405 in <nixpkgs>.

Add metadata about expected function arguments to a function. The metadata should match the format given by builtins.functionArgs, i.e. a set from expected argument to a bool representing whether that argument has a default or not. setFunctionArgs : (a → b) → Map String Bool → (a → b)

This function is necessary because you can't dynamically create a function of the { a, b ? foo, ... }: format, but some facilities like callPackage expect to be able to query expected arguments.

Located at lib/trivial.nix:428 in <nixpkgs>.

Extract the expected function arguments from a function. This works both with nix-native { a, b ? foo, ... }: style functions and functions with args set with 'setFunctionArgs'. It has the same return type and semantics as builtins.functionArgs. setFunctionArgs : (a → b) → Map String Bool.

Located at lib/trivial.nix:440 in <nixpkgs>.

Check whether something is a function or something annotated with function args.

Located at lib/trivial.nix:448 in <nixpkgs>.

Turns any non-callable values into constant functions. Returns callable values as is.

nix-repl> lib.toFunction 1 2
1

nix-repl> lib.toFunction (x: x + 1) 2
3

Located at lib/trivial.nix:463 in <nixpkgs>.

Convert the given positive integer to a string of its hexadecimal representation. For example:

toHexString 0 => "0"

toHexString 16 => "10"

toHexString 250 => "FA"

Located at lib/trivial.nix:479 in <nixpkgs>.

`toBaseDigits base i` converts the positive integer i to a list of its digits in the given base. For example:

toBaseDigits 10 123 => [ 1 2 3 ]

toBaseDigits 2 6 => [ 1 1 0 ]

toBaseDigits 16 250 => [ 15 10 ]

Located at lib/trivial.nix:505 in <nixpkgs>.

Create a list consisting of a single element. `singleton x` is sometimes more convenient with respect to indentation than `[x]` when x spans multiple lines.

singleton "foo"
=> [ "foo" ]

Located at lib/lists.nix:23 in <nixpkgs>.

Apply the function to each element in the list. Same as `map`, but arguments flipped.

forEach [ 1 2 ] (x:
toString x
)
=> [ "1" "2" ]

Located at lib/lists.nix:36 in <nixpkgs>.

“right fold” a binary function `op` between successive elements of `list` with `nul` as the starting value, i.e., `foldr op nul [x_1 x_2 ... x_n] == op x_1 (op x_2 ... (op x_n nul))`.

concat = foldr (a: b: a + b) "z"
concat [ "a" "b" "c" ]
=> "abcz"
# different types
strange = foldr (int: str: toString (int + 1) + str) "a"
strange [ 1 2 3 4 ]
=> "2345a"

Located at lib/lists.nix:53 in <nixpkgs>.

`fold` is an alias of `foldr` for historic reasons

Located at lib/lists.nix:64 in <nixpkgs>.

“left fold”, like `foldr`, but from the left: `foldl op nul [x_1 x_2 ... x_n] == op (... (op (op nul x_1) x_2) ... x_n)`.

lconcat = foldl (a: b: a + b) "z"
lconcat [ "a" "b" "c" ]
=> "zabc"
# different types
lstrange = foldl (str: int: str + toString (int + 1)) "a"
lstrange [ 1 2 3 4 ]
=> "a2345"

Located at lib/lists.nix:81 in <nixpkgs>.

Strict version of `foldl`.

The difference is that evaluation is forced upon access. Usually used with small whole results (in contrast with lazily-generated list or large lists where only a part is consumed.)

Located at lib/lists.nix:97 in <nixpkgs>.

Map with index starting from 0

imap0 (i: v: "${v}-${toString i}") ["a" "b"]
=> [ "a-0" "b-1" ]

Located at lib/lists.nix:107 in <nixpkgs>.

Map with index starting from 1

imap1 (i: v: "${v}-${toString i}") ["a" "b"]
=> [ "a-1" "b-2" ]

Located at lib/lists.nix:117 in <nixpkgs>.

Map and concatenate the result.

concatMap (x: [x] ++ ["z"]) ["a" "b"]
=> [ "a" "z" "b" "z" ]

Located at lib/lists.nix:127 in <nixpkgs>.

Flatten the argument into a single list; that is, nested lists are spliced into the top-level lists.

flatten [1 [2 [3] 4] 5]
=> [1 2 3 4 5]
flatten 1
=> [1]

Located at lib/lists.nix:138 in <nixpkgs>.

Remove elements equal to 'e' from a list. Useful for buildInputs.

remove 3 [ 1 3 4 3 ]
=> [ 1 4 ]

Located at lib/lists.nix:151 in <nixpkgs>.

Find the sole element in the list matching the specified predicate, returns `default` if no such element exists, or `multiple` if there are multiple matching elements.

findSingle (x: x == 3) "none" "multiple" [ 1 3 3 ]
=> "multiple"
findSingle (x: x == 3) "none" "multiple" [ 1 3 ]
=> 3
findSingle (x: x == 3) "none" "multiple" [ 1 9 ]
=> "none"

Located at lib/lists.nix:169 in <nixpkgs>.

Find the first element in the list matching the specified predicate or return `default` if no such element exists.

findFirst (x: x > 3) 7 [ 1 6 4 ]
=> 6
findFirst (x: x > 9) 7 [ 1 6 4 ]
=> 7

Located at lib/lists.nix:194 in <nixpkgs>.

Return true if function `pred` returns true for at least one element of `list`.

any isString [ 1 "a" { } ]
=> true
any isString [ 1 { } ]
=> false

Located at lib/lists.nix:215 in <nixpkgs>.

Return true if function `pred` returns true for all elements of `list`.

all (x: x < 3) [ 1 2 ]
=> true
all (x: x < 3) [ 1 2 3 ]
=> false

Located at lib/lists.nix:228 in <nixpkgs>.

Count how many elements of `list` match the supplied predicate function.

count (x: x == 3) [ 3 2 3 4 6 ]
=> 2

Located at lib/lists.nix:239 in <nixpkgs>.

Return a singleton list or an empty list, depending on a boolean value. Useful when building lists with optional elements (e.g. `++ optional (system == "i686-linux") firefox').

optional true "foo"
=> [ "foo" ]
optional false "foo"
=> [ ]

Located at lib/lists.nix:255 in <nixpkgs>.

Return a list or an empty list, depending on a boolean value.

optionals true [ 2 3 ]
=> [ 2 3 ]
optionals false [ 2 3 ]
=> [ ]

Located at lib/lists.nix:267 in <nixpkgs>.

If argument is a list, return it; else, wrap it in a singleton list. If you're using this, you should almost certainly reconsider if there isn't a more "well-typed" approach.

toList [ 1 2 ]
=> [ 1 2 ]
toList "hi"
=> [ "hi "]

Located at lib/lists.nix:284 in <nixpkgs>.

Return a list of integers from `first' up to and including `last'.

range 2 4
=> [ 2 3 4 ]
range 3 2
=> [ ]

Located at lib/lists.nix:296 in <nixpkgs>.

Splits the elements of a list in two lists, `right` and `wrong`, depending on the evaluation of a predicate.

partition (x: x > 2) [ 5 1 2 3 4 ]
=> { right = [ 5 3 4 ]; wrong = [ 1 2 ]; }

Located at lib/lists.nix:315 in <nixpkgs>.

Splits the elements of a list into many lists, using the return value of a predicate. Predicate should return a string which becomes keys of attrset `groupBy' returns.

`groupBy'` allows to customise the combining function and initial value

groupBy (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = [ 5 3 4 ]; false = [ 1 2 ]; }
groupBy (x: x.name) [ {name = "icewm"; script = "icewm &";}
{name = "xfce";  script = "xfce4-session &";}
{name = "icewm"; script = "icewmbg &";}
{name = "mate";  script = "gnome-session &";}
]
=> { icewm = [ { name = "icewm"; script = "icewm &"; }
{ name = "icewm"; script = "icewmbg &"; } ];
mate  = [ { name = "mate";  script = "gnome-session &"; } ];
xfce  = [ { name = "xfce";  script = "xfce4-session &"; } ];
}

groupBy' builtins.add 0 (x: boolToString (x > 2)) [ 5 1 2 3 4 ]
=> { true = 12; false = 3; }

Located at lib/lists.nix:344 in <nixpkgs>.

Merges two lists of the same size together. If the sizes aren't the same the merging stops at the shortest. How both lists are merged is defined by the first argument.

zipListsWith (a: b: a + b) ["h" "l"] ["e" "o"]
=> ["he" "lo"]

Located at lib/lists.nix:364 in <nixpkgs>.

Merges two lists of the same size together. If the sizes aren't the same the merging stops at the shortest.

zipLists [ 1 2 ] [ "a" "b" ]
=> [ { fst = 1; snd = "a"; } { fst = 2; snd = "b"; } ]

Located at lib/lists.nix:383 in <nixpkgs>.

Reverse the order of the elements of a list.

reverseList [ "b" "o" "j" ]
=> [ "j" "o" "b" ]

Located at lib/lists.nix:394 in <nixpkgs>.

Depth-First Search (DFS) for lists `list != []`.

`before a b == true` means that `b` depends on `a` (there's an edge from `b` to `a`).

listDfs true hasPrefix [ "/home/user" "other" "/" "/home" ]
== { minimal = "/";                  # minimal element
visited = [ "/home/user" ];     # seen elements (in reverse order)
rest    = [ "/home" "other" ];  # everything else
}

listDfs true hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
== { cycle   = "/";                  # cycle encountered at this element
loops   = [ "/" ];              # and continues to these elements
visited = [ "/" "/home/user" ]; # elements leading to the cycle (in reverse order)
rest    = [ "/home" "other" ];  # everything else

Located at lib/lists.nix:416 in <nixpkgs>.

Sort a list based on a partial ordering using DFS. This implementation is O(N^2), if your ordering is linear, use `sort` instead.

`before a b == true` means that `b` should be after `a` in the result.

toposort hasPrefix [ "/home/user" "other" "/" "/home" ]
== { result = [ "/" "/home" "/home/user" "other" ]; }

toposort hasPrefix [ "/home/user" "other" "/" "/home" "/" ]
== { cycle = [ "/home/user" "/" "/" ]; # path leading to a cycle
loops = [ "/" ]; }                # loops back to these elements

toposort hasPrefix [ "other" "/home/user" "/home" "/" ]
== { result = [ "other" "/" "/home" "/home/user" ]; }

toposort (a: b: a < b) [ 3 2 1 ] == { result = [ 1 2 3 ]; }

Located at lib/lists.nix:455 in <nixpkgs>.

Sort a list based on a comparator function which compares two elements and returns true if the first argument is strictly below the second argument. The returned list is sorted in an increasing order. The implementation does a quick-sort.

sort (a: b: a < b) [ 5 3 7 ]
=> [ 3 5 7 ]

Located at lib/lists.nix:483 in <nixpkgs>.

Compare two lists element-by-element.

compareLists compare [] []
=> 0
compareLists compare [] [ "a" ]
=> -1
compareLists compare [ "a" ] []
=> 1
compareLists compare [ "a" "b" ] [ "a" "c" ]
=> -1

Located at lib/lists.nix:512 in <nixpkgs>.

Sort list using "Natural sorting". Numeric portions of strings are sorted in numeric order.

naturalSort ["disk11" "disk8" "disk100" "disk9"]
=> ["disk8" "disk9" "disk11" "disk100"]
naturalSort ["10.46.133.149" "10.5.16.62" "10.54.16.25"]
=> ["10.5.16.62" "10.46.133.149" "10.54.16.25"]
naturalSort ["v0.2" "v0.15" "v0.0.9"]
=> [ "v0.0.9" "v0.2" "v0.15" ]

Located at lib/lists.nix:535 in <nixpkgs>.

Return the first (at most) N elements of a list.

take 2 [ "a" "b" "c" "d" ]
=> [ "a" "b" ]
take 2 [ ]
=> [ ]

Located at lib/lists.nix:553 in <nixpkgs>.

Remove the first (at most) N elements of a list.

drop 2 [ "a" "b" "c" "d" ]
=> [ "c" "d" ]
drop 2 [ ]
=> [ ]

Located at lib/lists.nix:567 in <nixpkgs>.

Return a list consisting of at most `count` elements of `list`, starting at index `start`.

sublist 1 3 [ "a" "b" "c" "d" "e" ]
=> [ "b" "c" "d" ]
sublist 1 3 [ ]
=> [ ]

Located at lib/lists.nix:584 in <nixpkgs>.

Return the last element of a list.

This function throws an error if the list is empty.

last [ 1 2 3 ]
=> 3

Located at lib/lists.nix:608 in <nixpkgs>.

Return all elements but the last.

This function throws an error if the list is empty.

init [ 1 2 3 ]
=> [ 1 2 ]

Located at lib/lists.nix:622 in <nixpkgs>.

Return the image of the cross product of some lists by a function.

crossLists (x:y: "${toString x}${toString y}") [[1 2] [3 4]]
=> [ "13" "14" "23" "24" ]

Located at lib/lists.nix:633 in <nixpkgs>.

Remove duplicate elements from the list. O(n^2) complexity.

unique [ 3 2 3 4 ]
=> [ 3 2 4 ]

Located at lib/lists.nix:646 in <nixpkgs>.

Intersects list 'e' and another list. O(nm) complexity.

intersectLists [ 1 2 3 ] [ 6 3 2 ]
=> [ 3 2 ]

Located at lib/lists.nix:654 in <nixpkgs>.

Subtracts list 'e' from another list. O(nm) complexity.

subtractLists [ 3 2 ] [ 1 2 3 4 5 3 ]
=> [ 1 4 5 ]

Located at lib/lists.nix:662 in <nixpkgs>.

Test if two lists have no common element. It should be slightly more efficient than (intersectLists a b == [])

Located at lib/lists.nix:667 in <nixpkgs>.

Conditionally trace the supplied message, based on a predicate.

traceIf true "hello" 3
trace: hello
=> 3

Located at lib/debug.nix:51 in <nixpkgs>.

Trace the supplied value after applying a function to it, and return the original value.

traceValFn (v: "mystring ${v}") "foo"
trace: mystring foo
=> "foo"

Located at lib/debug.nix:69 in <nixpkgs>.

Trace the supplied value and return it.

traceVal 42
# trace: 42
=> 42

Located at lib/debug.nix:84 in <nixpkgs>.

`builtins.trace`, but the value is `builtins.deepSeq`ed first.

trace { a.b.c = 3; } null
trace: { a = <CODE>; }
=> null
traceSeq { a.b.c = 3; } null
trace: { a = { b = { c = 3; }; }; }
=> null

Located at lib/debug.nix:98 in <nixpkgs>.

Like `traceSeq`, but only evaluate down to depth n. This is very useful because lots of `traceSeq` usages lead to an infinite recursion.

traceSeqN 2 { a.b.c = 3; } null
trace: { a = { b = {…}; }; }
=> null

Located at lib/debug.nix:113 in <nixpkgs>.

A combination of `traceVal` and `traceSeq` that applies a provided function to the value to be traced after `deepSeq`ing it.

Located at lib/debug.nix:130 in <nixpkgs>.

A combination of `traceVal` and `traceSeq`.

Located at lib/debug.nix:137 in <nixpkgs>.

A combination of `traceVal` and `traceSeqN` that applies a provided function to the value to be traced.

Located at lib/debug.nix:141 in <nixpkgs>.

A combination of `traceVal` and `traceSeqN`.

Located at lib/debug.nix:149 in <nixpkgs>.

Trace the input and output of a function `f` named `name`, both down to `depth`.

This is useful for adding around a function call, to see the before/after of values as they are transformed.

traceFnSeqN 2 "id" (x: x) { a.b.c = 3; }
trace: { fn = "id"; from = { a.b = {…}; }; to = { a.b = {…}; }; }
=> { a.b.c = 3; }

Located at lib/debug.nix:162 in <nixpkgs>.

Evaluate a set of tests. A test is an attribute set `{expr, expected}`, denoting an expression and its expected result. The result is a list of failed tests, each represented as `{name, expected, actual}`, denoting the attribute name of the failing test and its expected and actual results.

Used for regression testing of the functions in lib; see tests.nix for an example. Only tests having names starting with "test" are run.

Add attr { tests = ["testName"]; } to run these tests only.

Located at lib/debug.nix:188 in <nixpkgs>.

Create a test assuming that list elements are `true`.

{ testX = allTrue [ true ]; }

Located at lib/debug.nix:204 in <nixpkgs>.

Returns true when the given argument is an option

isOption 1             // => false
isOption (mkOption {}) // => true

Located at lib/options.nix:50 in <nixpkgs>.

Creates an Option attribute set. mkOption accepts an attribute set with the following keys:

All keys default to `null` when not given.

mkOption { }  // => { _type = "option"; }
mkOption { default = "foo"; } // => { _type = "option"; default = "foo"; }

Located at lib/options.nix:60 in <nixpkgs>.

Creates an Option attribute set for a boolean value option i.e an option to be toggled on or off:

mkEnableOption "foo"
=> { _type = "option"; default = false; description = "Whether to enable foo."; example = true; type = { ... }; }

Located at lib/options.nix:92 in <nixpkgs>.

Creates an Option attribute set for an option that specifies the package a module should use for some purpose.

mkPackageOption pkgs "hello" { }
=> { _type = "option"; default = «derivation /nix/store/3r2vg51hlxj3cx5vscp0vkv60bqxkaq0-hello-2.10.drv»; defaultText = { ... }; description = "The hello package to use."; type = { ... }; }


mkPackageOption pkgs "GHC" {
default = [ "ghc" ];
example = "pkgs.haskell.packages.ghc92.ghc.withPackages (hkgs: [ hkgs.primes ])";
}
=> { _type = "option"; default = «derivation /nix/store/jxx55cxsjrf8kyh3fp2ya17q99w7541r-ghc-8.10.7.drv»; defaultText = { ... }; description = "The GHC package to use."; example = { ... }; type = { ... }; }

Located at lib/options.nix:130 in <nixpkgs>.

Like mkPackageOption, but emit an mdDoc description instead of DocBook.

Located at lib/options.nix:148 in <nixpkgs>.

This option accepts anything, but it does not produce any result.

This is useful for sharing a module across different module sets without having to implement similar features as long as the values of the options are not accessed.

Located at lib/options.nix:157 in <nixpkgs>.

"Merge" option definitions by checking that they all have the same value.

Located at lib/options.nix:190 in <nixpkgs>.

Extracts values of all "value" keys of the given list.

getValues [ { value = 1; } { value = 2; } ] // => [ 1 2 ]
getValues [ ]                               // => [ ]

Located at lib/options.nix:210 in <nixpkgs>.

Extracts values of all "file" keys of the given list

getFiles [ { file = "file1"; } { file = "file2"; } ] // => [ "file1" "file2" ]
getFiles [ ]                                         // => [ ]

Located at lib/options.nix:220 in <nixpkgs>.

This function recursively removes all derivation attributes from `x` except for the `name` attribute.

This is to make the generation of `options.xml` much more efficient: the XML representation of derivations is very large (on the order of megabytes) and is not actually used by the manual generator.

Located at lib/options.nix:265 in <nixpkgs>.

For use in the `defaultText` and `example` option attributes. Causes the given string to be rendered verbatim in the documentation as Nix code. This is necessary for complex values, e.g. functions, or values that depend on other values or packages.

Located at lib/options.nix:278 in <nixpkgs>.

For use in the `defaultText` and `example` option attributes. Causes the given DocBook text to be inserted verbatim in the documentation, for when a `literalExpression` would be too hard to read.

Located at lib/options.nix:289 in <nixpkgs>.

Transition marker for documentation that's already migrated to markdown syntax.

Located at lib/options.nix:299 in <nixpkgs>.

For use in the `defaultText` and `example` option attributes. Causes the given MD text to be inserted verbatim in the documentation, for when a `literalExpression` would be too hard to read.

Located at lib/options.nix:307 in <nixpkgs>.

Convert an option, described as a list of the option parts in to a safe, human readable version.

(showOption ["foo" "bar" "baz"]) == "foo.bar.baz"
(showOption ["foo" "bar.baz" "tux"]) == "foo.bar.baz.tux"

Placeholders will not be quoted as they are not actual values:
(showOption ["foo" "*" "bar"]) == "foo.*.bar"
(showOption ["foo" "<name>" "bar"]) == "foo.<name>.bar"

Unlike attributes, options can also start with numbers:
(showOption ["windowManager" "2bwm" "enable"]) == "windowManager.2bwm.enable"

Located at lib/options.nix:327 in <nixpkgs>.

A map of all haskell packages defined in the given path, identified by having a cabal file with the same name as the directory itself.

Located at lib/filesystem.nix:18 in <nixpkgs>.

Find the first directory containing a file matching 'pattern' upward from a given 'file'. Returns 'null' if no directories contain a file matching 'pattern'.

Located at lib/filesystem.nix:41 in <nixpkgs>.

Given a directory, return a flattened list of all files within it recursively.

Located at lib/filesystem.nix:69 in <nixpkgs>.

Returns the type of a path: regular (for file), symlink, or directory.

Located at lib/sources.nix:274 in <nixpkgs>.

Returns true if the path exists and is a directory, false otherwise.

Located at lib/sources.nix:274 in <nixpkgs>.

Returns true if the path exists and is a regular file, false otherwise.

Located at lib/sources.nix:274 in <nixpkgs>.

A basic filter for `cleanSourceWith` that removes directories of version control system, backup files (*~) and some generated files.

Located at lib/sources.nix:274 in <nixpkgs>.

Filters a source tree removing version control files and directories using cleanSourceFilter.

cleanSource ./.

Located at lib/sources.nix:274 in <nixpkgs>.

Like `builtins.filterSource`, except it will compose with itself, allowing you to chain multiple calls together without any intermediate copies being put in the nix store.

lib.cleanSourceWith {
filter = f;
src = lib.cleanSourceWith {
filter = g;
src = ./.;
};
}
# Succeeds!

builtins.filterSource f (builtins.filterSource g ./.)
# Fails!

Located at lib/sources.nix:274 in <nixpkgs>.

Add logging to a source, for troubleshooting the filtering behavior.

Located at lib/sources.nix:274 in <nixpkgs>.

Filter sources by a list of regular expressions.

src = sourceByRegex ./my-subproject [".*\.py$" "^database.sql$"]

Located at lib/sources.nix:274 in <nixpkgs>.

Get all files ending with the specified suffices from the given source directory or its descendants, omitting files that do not match any suffix. The result of the example below will include files like `./dir/module.c` and `./dir/subdir/doc.xml` if present.

sourceFilesBySuffices ./. [ ".xml" ".c" ]

Located at lib/sources.nix:274 in <nixpkgs>.

Get the commit id of a git repo.

commitIdFromGitRepo <nixpkgs/.git>

Located at lib/sources.nix:274 in <nixpkgs>.