proplists(3erl)

okay bestie, welcome to proplists(3erl) — the Erlang Module Definition page, part 1 🫶. This is literally the support-functions era for property lists, and we’re getting through every export together. 💅

🌟 NAME 🌟

proplists — support functions for property lists. That’s the whole assignment. ✨

💫 DESCRIPTION 💫

Property lists are ordinary lists, bestie. Their entries are either tuples, whose first elements are keys used for lookup and insertion, or atoms, which work as shorthand for tuples {Atom, true}. Other terms are allowed in the lists, but this module ignores them. If there is more than one entry in a list for a certain key, the first occurrence normally overrides any later — and yes, that’s irrespective of the arity of the tuples. 👑

Property lists are useful for representing inherited properties, such as options passed to a function where a user can specify options overriding the default settings, object properties, annotations, and so on. It’s giving config inheritance, fr fr. 🧚

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. no cap. 💀

🦋 DATA TYPES 🦋

property() = atom() | tuple()
proplist() = [property()]

✨ EXPORTS ✨

🌸 append_values(Key, ListIn) -> ListOut 🌸

Types:

Key = term()
ListIn = 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 💜

Types:

ListIn = 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 🍓

Types:

Key = term()
List = [term()]

Deletes all entries associated with Key from List. bye-bye entries 👋

🦋 expand(Expansions, ListIn) -> ListOut 🦋

Types:

Expansions = [{Property :: property(), Expansion :: [term()]}]
ListIn = 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 🌈

Types:

Map = #{Key => Value}
List = [{Key, Value}]
Key = Value = term()

Converts the map Map to a property list. map to proplist pipeline, slay 🗺️ → 📋

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

Types:

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. all the values, no gatekeeping 💅

🌸 get_bool(Key, List) -> boolean() 🌸

Types:

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()] ⭐

Types:

List = [term()]

Returns an unordered list of the keys used in List, not containing duplicates. key collection era 👑

💖 get_value(Key, List) -> term() 💖

Types:

Key = term()
List = [term()]

Equivalent to get_value(Key, List, undefined). default mode activated ✨

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

Types:

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. fallback bestie is here 💅

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

🦋 is_defined(Key, List) -> boolean() 🦋

Types:

Key = term()
List = [term()]

Returns true if List contains at least one entry associated with Key, otherwise false. vibe check for keys ✅

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

Types:

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. first match gets the crown 👑

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

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

Types:

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. collect all the matching entries, bestie 🎀

See also lookup/2.

🧚 normalize(ListIn, Stages) -> ListOut 🧚

Types:

ListIn = [term()]
Stages = [Operation]
Operation =
    {aliases, Aliases} |
    {negations, Negations} |
    {expand, Expansions}
Aliases = 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. it’s giving layered glow-up 💅

See also substitute_negations/2.

🎀 property(PropertyIn) -> PropertyOut 🎀

Types:

PropertyIn = 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. minimal queen behavior 👑

See also property/2.

💜 property(Key, Value) -> Property 💜

Types:

Key = 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. cute little normalizer 🎀

See also property/1.

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

Types:

List = 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. sorting into friend groups, but make it functional 🫶

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 🌈

Types:

Aliases = [{Key, Key}]
Key = term()
ListIn = 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. alias glow-up, periodt ✨

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 🌸

Types:

Negations = [{Key1, Key2}]
Key1 = Key2 = term()
ListIn = ListOut = [term()]

Substitutes keys of boolean-valued properties and simultaneously negates their values. For each entry in ListIn, if it is 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. flip era 🔄

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.

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

🦋 to_map(List) -> Map 🦋

Types:

List = [Shorthand | {Key, Value} | term()]
Map = #{Shorthand => true, Key => Value}
Shorthand = atom()
Key = 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. silent treatment, but make it data structure conversion 💅

If the same Key shows up in List more than once, bestie, the value from the copy nearest to the head of List wins — that's literally the value get_value(Key, List) would hand you. No cap. ✨

Example, because we love a visual:

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

returns:

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

to_map(List, Stages) -> Map

Types:

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

This one is giving glow-up energy: it converts the property list List into a map after applying the normalizations given in Stages. Obsessed. 💅

See also normalize/2, to_map/1. 🫶

unfold(ListIn) -> ListOut

Types:

ListIn = ListOut = [term()]

Unfolds every single occurrence of atoms in ListIn into tuples {Atom, true}. Slay. 🦋

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Okay bestie, that's the whole iconic page 💖 brought to you by Ericsson AB, stdlib 4.3.1.3, and proplists(3erl) — periodt. 🎀