(* Core Character Sequences *)

white_space         ::= '\u0020' | '\u0009' | '\u000D' | '\u000A'
paren               ::= '(' | ')';
bracket             ::= '[' | ']';
brace               ::= '{' | '}';
digit               ::= '0' | '1' | '2' | '3' | '4' | '5' | '6' | '7' | '8' | '9';
hex                 ::= '0' | ... | '9' | 'A' | ... | 'F' | 'a' | ... | 'f' ;
upper               ::= 'A' | ... | 'Z' | Lu | Lt | Nl
                      | Lo upper only
                      | Lm upper only;
lower               ::= 'a' | ... | 'z' | Ll
                      | Lo lower only
                      | Lm lower only;
letter              ::= upper | lower;
escape_unicode      ::= '\', 'u', hex, hex, hex, hex;
escape_char         ::= '\', ('b' | 'f' | 'n' | 'r' | 't' | '\' | '"');
escape_seq          ::= escape_unicode | escape_char;
number_integer      ::= '0' | digit, [{digit}];
number_float        ::= number_integer, '.', number_integer;
newline             ::= '\n';
printable_char      ::= printable utf8;
char_char           ::= printable_char without newline or single quote
                      | escape_seq;
string_char         ::= printable_char without newline or double quote
                      | escape_seq;

(* Comments *)

comment             ::= '-', '-', {utf8};
docstring           ::= '-', '-', '-', {utf8};

(* Literal Values *)

literal_bool        ::= 'true' | 'false';
literal_integer     ::= ['-'], number_integer;
literal_float       ::= ['-'], number_float;
literal_char        ::= "'", char_char, "'";
literal_string      ::= '"', {string_char}, "'";
empty_tuple         ::= '(', ')';
literal             ::= literal_bool
                      | literal_integer
                      | literal_float
                      | literal_char
                      | literal_string
                      | empty_tuple;

(* Keywords *)

k_type              ::= 't', 'y', 'p', 'e';
k_class             ::= 'c', 'l', 'a', 's', 's';
k_alias             ::= 'a', 'l', 'i', 'a', 's';
k_const             ::= 'c', 'o', 'n', 's', 't';
k_enum              ::= 'e', 'n', 'u', 'm';
k_record            ::= 'r', 'e', 'c', 'o', 'r', 'd';
k_object            ::= 'o', 'b', 'j', 'e', 'c', 't';
k_let               ::= 'l', 'e', 't';
k_mut               ::= 'm', 'u', 't';
k_export            ::= 'e', 'x', 'p', 'o', 'r', 't';
k_import            ::= 'i', 'm', 'p', 'o', 'r', 't';
k_namespace         ::= 'n', 'a', 'm', 'e', 's', 'p', 'a', 'c', 'e';
k_infix             ::= 'i', 'n', 'f', 'i', 'x';
k_fn                ::= 'f', 'n';
k_end               ::= 'e', 'n', 'd';
k_match             ::= 'm', 'a', 't', 'c', 'h';
k_case              ::= 'c', 'a', 's', 'e';
k_if                ::= 'i', 'f';
k_then              ::= 't', 'h', 'e', 'n';
k_else              ::= 'e', 'l', 's', 'e';
k_do                ::= 'd', 'o';
k_return            ::= 'r', 'e', 't', 'u', 'r', 'n';
k_given             ::= 'g', 'i', 'v', 'e', 'n';
k_true              ::= 't', 'r', 'u', 'e';
k_false             ::= 'f', 'a', 'l', 's', 'e';
keyword             ::= k_type | k_class | k_alias | k_const | k_enum | k_record
                      | k_object | k_let | k_mut | k_export | k_import
                      | k_namespace | k_infix | k_fn | k_end | k_match | k_case
                      | k_if | k_then | k_else | k_do | k_return | k_given
                      | k_true | k_false;