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atomic_list_concat/3

Module​

Built-in predicate.

Description​

Unifies Atom with the concatenation of the atomic textual representation of each element in List, inserting Separator between adjacent elements.

where:

  • List is a proper list of ground terms. Each element is converted using term_to_atom/2, so atoms, numbers, double-quoted strings, lists and compounds are supported;
  • Separator is an atom inserted between adjacent elements;
  • Atom is an atom representing the concatenation of the textual representation of each element in List.

Throws:

  • error(instantiation_error, atomic_list_concat/3) when List or Separator is insufficiently instantiated;
  • error(type_error(list, List), atomic_list_concat/3) when List is not a proper list;
  • error(type_error(atom, Separator), atomic_list_concat/3) when Separator is instantiated but is not an atom.

Signature​

atomic_list_concat(+List, +Separator, ?Atom) is det

Examples​

Concatenate values with a separator​

This scenario demonstrates how atomic_list_concat/3 inserts a separator between the textual representation of each list element.

Here are the steps of the scenario:

  • Given the program:
  • Given the query:
atomic_list_concat([cosmos, hub, 4], '-', Atom).
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 5580
answer:
  has_more: false
  variables: ["Atom"]
  results:
  - substitutions:
    - variable: Atom
      expression: "'cosmos-hub-4'"

Build a URI-like atom from separate parts​

This scenario demonstrates how atomic_list_concat/3 can be used to assemble a structured atom from reusable parts.

Here are the steps of the scenario:

  • Given the program:
  • Given the query:
atomic_list_concat([scheme, host, path], '://', URI).
  • When the query is run
  • Then the answer we get is:
height: 42
gas_used: 5879
answer:
  has_more: false
  variables: ["URI"]
  results:
  - substitutions:
    - variable: URI
      expression: "'scheme://host://path'"