Waddle_Language/grammar/declarations/function_declarations.bnf

<function_declaration> ::= <accessibility_modifier>"fn" <identifier> 
    <function_signature> 
    ["fails" "with" <error_type_list>]? 
    "{" <statement>* "}"

<function_signature> ::= "(" <parameter_list>? ")" 
    "->" <return_type_list>

<error_type_list> ::= <error_type> ("," <error_type>)*

<error_type> ::= <identifier> ["/" <identifier>]?

<parameter_list> ::=
    <parameter_group>?

<parameter_group> ::=
    <required_parameters>
    | <required_parameters> "," <default_parameters>
    | <default_parameters>

<required_parameters> ::=
    <required_parameter>
    | <required_parameter> "," <required_parameters>

<default_parameters> ::=
    <default_parameter>
    | <default_parameter> "," <default_parameters>

<required_parameter> ::= <parameter_type> <identifier>

<default_parameter> ::= <parameter_type> <identifier> ".default(" <literal> ")"

<lambda_declaration> ::= "fn" "(" <parameter_list>? ")" 
    "->" "[" <type> "]" 
    "{" <statement>* "}"