Class

A class is a collection of objects, similar to proper classes in Set theory.

Any object satisfying the constraints of a class belongs to it. Therefore, an object does not have a single type.

A class is defined structurally from a type expression, and can optionally have constraint expressions to verify if the object satisfy the desired properties.

Syntax

class_definition
class [ type_expression ] { pattern_matching_clause , , }
Show source 
class_definition
  = "class" "[" type_expression "]"
  ("{" pattern_matching_clause ("," pattern_matching_clause)* ","? "}")?
type_expression
type_expression & type_expression type_expression | type_expression ! type_expression ( type_expression ) type_term
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type_expression
  = (type_expression "&" type_expression)
  / (type_expression "|" type_expression)
  / ("!" type_expression)
  / ("(" type_expression ")")
  / type_term
type_term
type_ref type_literal type_tuple type_namedtuple
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type_term
  = type_ref
  / type_literal
  / type_tuple
  / type_namedtuple
type_ref
symbol_path < type_expression , , >
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type_ref
  = symbol_path ("<" type_expression ("," type_expression)* ","? ">")?
type_literal
atom bool number string
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type_literal
  = atom / bool / number / string
type_tuple
( ) ( type_expression , ) ( type_expression , type_expression , )
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type_tuple
  = ( "(" ")" )
  / ( "(" type_expression "," ")" )
  / ( "(" type_expression ("," type_expression)+ ","? ")" )
type_namedtuple
{ } { type_namedtuple_pair , , }
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type_namedtuple
  = ( "{" "}" )
  / ( "{" type_namedtuple_pair ("," type_namedtuple_pair)* ","? "}" )
type_namedtuple_pair
identifier : type_expression
Show source 
type_namedtuple_pair
  = identifier ":" type_expression

Examples

let even: class[int] {
  (n) -> n % 2 = 0,
};

let odd: class[int & !even];

let ok<t>: class[(@ok, t)];
let err<e>: class[(@error, e)];
let result<t, e>: class[ok<t> | err<e>];

Semantics

Each clause of a class MUST evaluate to a boolean (true or false).

If an exception is thrown in the body of a clause, it SHOULD be ignored and be equivalent to returning false.