proplists(3)

okay bestie, welcome to proplists(3) — Erlang Module Definition. this is part 1, so don't think we're done. 💅

✨ NAME ✨

proplists — Support functions for property lists. periodt. 🎀

🦋 DESCRIPTION 🦋

Property lists are ordinary lists, but they're serving looks. They contain entries in the form of either:

• tuples, whose first elements are keys used for lookup and insertion, or
• atoms, which work as shorthand for tuples {Atom, true}.

(Other terms? They're allowed in the lists, but this module ignores them. Not their moment.)

If there's more than one entry in a list for a certain key, the first occurrence normally overrides any later one — irrespective of the arity of the tuples. first come, first served, no cap.

Property lists are useful for representing inherited properties, like options passed to a function where a user can specify options overriding the default settings, object properties, annotations, and so on. it's giving "defaults but customizable."

Two keys are considered equal if they match (=:=). That means numbers are compared literally rather than by value, so for example, 1 and 1.0 are different keys. yes, literally different. 🙈

💖 DATA TYPES 💖

property() :: atom() | tuple().

A property item within a list. ✨

proplist() :: [property()].

A list of property/0, also knows as a proplist. (Keeping that "knows" exactly, bestie. 💅)

💅 FUNCTIONS 💅

append_values(Key, ListIn) -> ListOut

append_values(Key, ListIn) -> ListOut
                              when
                                  Key :: term(),
                                  ListIn :: [term()],
                                  ListOut :: [term()].

Similar to get_all_values/2, but each value is wrapped in a list unless it is already itself a list. The resulting list of lists is concatenated. This is often useful for "incremental" options.

Example:

append_values(a, [{a, [1,2]}, {b, 0}, {a, 3}, {c, -1}, {a, [4]}])

returns:

[1,2,3,4]

compact(ListIn) -> ListOut

compact(ListIn) -> ListOut
                when ListIn :: [property()], ListOut :: [property()].

Minimizes the representation of all entries in the list. This is equivalent to [property(P) || P <- ListIn].

See also property/1, unfold/1.

delete(Key, List) -> List

delete(Key, List) -> List when Key :: term(), List :: [term()].

Deletes all entries associated with Key from List. all of them. periodt.

expand(Expansions, ListIn) -> ListOut

expand(Expansions, ListIn) -> ListOut
                       when
                           Expansions ::
                               [{Property :: property(), Expansion ::
       [term()]}],
                           ListIn :: [term()],
                           ListOut :: [term()].

Expands particular properties to corresponding sets of properties (or other terms).

For each pair {Property, Expansion} in Expansions: if E is the first entry in ListIn with the same key as Property, and E and Property have equivalent normal forms, then E is replaced with the terms in Expansion, and any following entries with the same key are deleted from ListIn.

For example, the following expressions all return [fie, bar, baz, fum]:

expand([{foo, [bar, baz]}], [fie, foo, fum])
expand([{{foo, true}, [bar, baz]}], [fie, foo, fum])
expand([{{foo, false}, [bar, baz]}], [fie, {foo, false}, fum])

However, no expansion is done in the following call because {foo, false} shadows foo:

expand([{{foo, true}, [bar, baz]}], [{foo, false}, fie, foo, fum])

Notice that if the original property term is to be preserved in the result when expanded, it must be included in the expansion list. The inserted terms are not expanded recursively. If Expansions contains more than one property with the same key, only the first occurrence is used.

See also normalize/2.

from_map(Map) -> List

from_map(Map) -> List
                 when
                     Map :: #{Key => Value},
                     List :: [{Key, Value}],
                     Key :: term(),
                     Value :: term().

Converts the map Map to a property list. slay.

get_all_values(Key, List) -> [term()]

get_all_values(Key, List) -> [term()]
                               when Key :: term(), List :: [term()].

Similar to get_value/2, but returns the list of values for all entries {Key, Value} in List. If no such entry exists, the result is the empty list. no crumbs.

get_bool(Key, List) -> boolean()

get_bool(Key, List) -> boolean()
                         when Key :: term(), List :: [term()].

Returns the value of a boolean key/value option. If lookup(Key, List) would yield {Key, true}, this function returns true, otherwise false.

See also get_value/2, lookup/2.

get_keys(List) -> [term()]

get_keys(List) -> [term()] when List :: [term()].

Returns an unordered list of the keys used in List, not containing duplicates. it's giving unique.

get_value(Key, List, Default) -> term()

get_value(Key, List, Default) -> term()
                          when
                              Key :: term(),
                              List :: [term()],
                              Default :: term().

Returns the value of a simple key/value property in List. If lookup(Key, List) would yield {Key, Value}, this function returns the corresponding Value, otherwise Default.

See also get_all_values/2, get_bool/2, get_value/2, lookup/2.

is_defined(Key, List) -> boolean()

is_defined(Key, List) -> boolean()
                           when Key :: term(), List :: [term()].

Returns true if List contains at least one entry associated with Key, otherwise false. existence check, bestie.

lookup(Key, List) -> none | tuple()

lookup(Key, List) -> none | tuple()
                       when Key :: term(), List :: [term()].

Returns the first entry associated with Key in List, if one exists, otherwise returns none. For an atom A in the list, the tuple {A, true} is the entry associated with A.

See also get_bool/2, get_value/2, lookup_all/2.

lookup_all(Key, List) -> [tuple()]

lookup_all(Key, List) -> [tuple()]
                           when Key :: term(), List :: [term()].

Returns the list of all entries associated with Key in List. If no such entry exists, the result is the empty list.

See also lookup/2.

normalize(ListIn, Stages) -> ListOut

normalize(ListIn, Stages) -> ListOut
                          when
                              ListIn :: [term()],
                              Stages :: [Operation],
                              Operation ::
                                  {aliases, Aliases} |
                                  {negations, Negations} |
                                  {expand, Expansions},
                              Aliases :: [{Key, Key}],
                              Negations :: [{Key, Key}],
                              Expansions ::
                                  [{Property :: property(),
                                    Expansion :: [term()]}],
                              ListOut :: [term()].

Passes ListIn through a sequence of substitution/expansion stages. For an aliases operation, function substitute_aliases/2 is applied using the specified list of aliases:

• For a negations operation, substitute_negations/2 is applied using the specified negation list.
• For an expand operation, function expand/2 is applied using the specified list of expansions.

The final result is automatically compacted (compare compact/1).

Typically you want to substitute negations first, then aliases, then perform one or more expansions (sometimes you want to pre-expand particular entries before doing the main expansion). You might want to substitute negations and/or aliases repeatedly, to allow such forms in the right-hand side of aliases and expansion lists.

See also substitute_negations/2.

property(PropertyIn) -> PropertyOut

property(PropertyIn) -> PropertyOut
                         when
                             PropertyIn :: property(),
                             PropertyOut :: property().

Creates a normal form (minimal) representation of a property. If PropertyIn is {Key, true}, where Key is an atom, Key is returned, otherwise the whole term PropertyIn is returned.

See also property/2.

property(Key, Value) -> Property

property(Key, Value) -> Property
                         when
                             Key :: term(),
                             Value :: term(),
                             Property :: atom() | {term(), term()}.

Creates a normal form (minimal) representation of a simple key/value property. Returns Key if Value is true and Key is an atom, otherwise a tuple {Key, Value} is returned.

See also property/1.

split(List, Keys) -> {Lists, Rest}

split(List, Keys) -> {Lists, Rest}
                      when
                          List :: [term()],
                          Keys :: [term()],
                          Lists :: [[term()]],
                          Rest :: [term()].

Partitions List into a list of sublists and a remainder.

Lists contains one sublist for each key in Keys, in the corresponding order. The relative order of the elements in each sublist is preserved from the original List. Rest contains the elements in List that are not associated with any of the specified keys, also with their original relative order preserved.

Example:

split([{c, 2}, {e, 1}, a, {c, 3, 4}, d, {b, 5}, b], [a, b, c])

returns:

{[[a], [{b, 5}, b],[{c, 2}, {c, 3, 4}]], [{e, 1}, d]}

substitute_aliases(Aliases, ListIn) -> ListOut

substitute_aliases(Aliases, ListIn) -> ListOut
                                   when
                                       Aliases :: [{Key, Key}],
                                       Key :: term(),
                                       ListIn :: [term()],
                                       ListOut :: [term()].

Substitutes keys of properties. For each entry in ListIn, if it is associated with some key K1 such that {K1, K2} occurs in Aliases, the key of the entry is changed to K2. If the same K1 occurs more than once in Aliases, only the first occurrence is used.

For example, substitute_aliases([{color, colour}], L) replaces all tuples {color, ...} in L with {colour, ...}, and all atoms color with colour.

See also normalize/2, substitute_negations/2.

substitute_negations(Negations, ListIn) -> ListOut

substitute_negations(Negations, ListIn) -> ListOut
                                     when
                                         Negations :: [{Key1, Key2}],
                                         Key1 :: term(),
                                         Key2 :: term(),
                                         ListIn :: [term()],
                                         ListOut :: [term()].

Substitutes keys of boolean-valued properties and simultaneously negates their values. 💅

For each entry in ListIn, if it's associated with some key K1 such that {K1, K2} occurs in Negations: if the entry was {K1, true}, it is replaced with {K2, false}, otherwise with K2, thus changing the name of the option and simultaneously negating the value specified by get_bool(Key, ListIn). If the same K1 occurs more than once in Negations, only the first occurrence is used. Only the first one, bestie! No cap. 💅

For example, substitute_negations([{no_foo, foo}], L) replaces any atom no_foo or tuple {no_foo, true} in L with {foo, false}, and any other tuple {no_foo, ...} with foo. It's giving negation glow-up ✨.

See also get_bool/2, normalize/2, substitute_aliases/2.

💖 to_map(List) -> Map 💖

       to_map(List) -> Map
                       when
                           List :: [Shorthand | {Key, Value} | term()],
                           Map :: #{Shorthand => true, Key => Value},
                           Shorthand :: atom(),
                           Key :: term(),
                           Value :: term().

Converts the property list List to a map.

Shorthand atom values in List will be expanded to an association of the form Atom => true. Tuples of the form {Key, Value} in List will be converted to an association of the form Key => Value. Anything else will be silently ignored. Not a single peep. 🙈

If the same key appears in List multiple times, the value of the one appearing nearest to the head of List will be in the result map, that is the value that would be returned by a call to get_value(Key, List). So like, the first one wins, periodt. 👑

Example:

                     to_map([a, {b, 1}, {c, 2}, {c, 3}])

returns:

                     #{a => true, b => 1, c => 2}

✨ to_map(List, Stages) -> Map ✨

       to_map(List, Stages) -> Map
                       when
                           List :: [term()],
                           Stages :: [Operation],
                           Operation ::
                               {aliases, Aliases} |
                               {negations, Negations} |
                               {expand, Expansions},
                           Aliases :: [{Key, Key}],
                           Negations :: [{Key, Key}],
                           Expansions ::
                               [{Property :: property(), Expansion ::
       [term()]}],
                           Map :: #{term() => term()}.

Converts the property list List to a map after applying the normalizations given in Stages. It's like a makeover montage for your proplist. 💅

See also normalize/2, to_map/1.

🦋 unfold(ListIn) -> ListOut 🦋

       unfold(ListIn) -> ListOut
                       when ListIn :: [term()], ListOut :: [term()].

Unfolds all occurrences of atoms in ListIn to tuples {Atom, true}. Giving them their true form, y'know? 🦋

See also compact/1.

---

And that's the tea, bestie! 🎀 This page is from Ericsson AB, stdlib 8.0.4, and it's the proplists(3) manual. (No date in the footer, but we still stan.) Stay iconic, keep your property lists normalized, and remember: only the first occurrence matters. 💅✨