expression ->
	| sequence
	| apply
	| unary
	| binary
	| let
	| control
	| primary

grouping -> "(" expression ")" ;
unary -> ( "-" | "!" ) expression ;
binary -> expression operator expression ;
operator ->
	| "==" | "!=" | "<" | "<=" | ">" | ">="
	| "+" | "-" | "*" | "/"
	| "++" ;
pattern -> "_" | record_pattern | variant_pattern ;
record_pattern -> "{" ( identifier ( "=" pattern )? ( "," identifier ( "=" pattern )? )* ) ( "|" identifier ) "}"
variant_pattern -> "`" identifier ( "(" ( "_" | compound_pattern | identifier ) ")" )? ;
parameters -> "(" ( identifier ( "," identifier )* )?")"
let -> "let" ( identifier parameters? | pattern ) "=" expression ( "and" ( identifier parameters? | pattern ) "=" expression )* "in" expression ;
control ->
	| if
	| when
if -> "if" expression "then" expression "else" expression ;
when -> "when" expression "is" ( ( identifier | pattern ) "=>" expression )+ ;
variant -> "`" identifier ( "(" expression ")" )? ;
base_record -> expression ( "with" identifier "=" expression ( "," identifier "=" expression )* ","? )?
record ->
	"{" ( identifier ("=" expression)? ( "," identifier ("=" expression)? )* )? ( "|" base_record )? "}" ;
list -> "[" ( expression ( "," expression )* ","? )? "]" ;
identifier -> IDENTIFIER | "@" STRING ;
operand -> ( NUMBER | STRING | identifier | "(" expression ")" | record | variant | list) ;
selector -> "." identifier ;
index -> "[" expression "]" ;
call -> "(" ( ( "_" | expression ) ( "," ( "_" | expression ) )* ","? )? ")" ;
primary -> operand ( selector | index | call ) ;