grammar Qrb::Syntax::Parser

  rule system
    (spacing definitions spacing type? spacing eof)
    <Qrb::Syntax::System>
  end

  rule definitions
    (type_def (spacing type_def)*)?
    <Qrb::Syntax::Definitions>
  end

  ###################################################################### Types
  rule type_def
    (type_name spacing '=' spacing type)
    <Qrb::Syntax::TypeDef>
  end

  rule type
    union_type
  end

  # union and sub types

  rule union_type
      (sub_type ('|' sub_type)+)
      <Qrb::Syntax::UnionType>
    | sub_type
  end

  rule sub_type
      (rel_type constraint_def)
      <Qrb::Syntax::SubType>
    | rel_type
  end

  rule constraint_def
    ('(' spacing var_name spacing '|' spacing constraints spacing ')')
    <Qrb::Syntax::ConstraintDef>
  end

  rule constraints
      (named_constraint (spacing ',' spacing named_constraint)*)
      <Qrb::Syntax::Constraints>
    | unnamed_constraint
  end

  rule named_constraint
    (constraint_name ':' spacing expression)
    <Qrb::Syntax::NamedConstraint>
  end

  rule unnamed_constraint
    (spacing expression)
    <Qrb::Syntax::UnnamedConstraint>
  end

  # relational types

  rule rel_type
      relation_type
    | tuple_type
    | collection_type
  end

  rule relation_type
    ('{{' spacing heading spacing '}}')
    <Qrb::Syntax::RelationType>
  end

  rule tuple_type
    ('{' spacing heading spacing '}')
    <Qrb::Syntax::TupleType>
  end

  rule heading
      (attribute (',' spacing attribute)*)
      <Qrb::Syntax::Heading>
    | spacing
      <Qrb::Syntax::Heading>
  end

  rule attribute
    (attribute_name spacing ':' spacing type)
    <Qrb::Syntax::Attribute>
  end

  # collection types

  rule collection_type
      set_type
    | seq_type
    | term_type
  end

  rule set_type
    ('{' type '}')
    <Qrb::Syntax::SetType>
  end

  rule seq_type
    ('[' type ']')
    <Qrb::Syntax::SeqType>
  end

  # terminal forms

  rule term_type
      ad_type
    | builtin_type
    | type_ref
  end

  # ad type

  rule ad_type
    (('.' builtin_type_name)? spacing contract (spacing ',' spacing contract)*)
    <Qrb::Syntax::AdType>
  end

  rule contract
    ('<' contract_name '>' spacing type (spacing ('\\' up:lambda_expr) spacing ('\\' down:lambda_expr))?)
    <Qrb::Syntax::Contract>
  end

  # builtin and refs

  rule builtin_type
    ('.' builtin_type_name)
    <Qrb::Syntax::BuiltinType>
  end

  rule type_ref
    (type_name spacing)
    <Qrb::Syntax::TypeRef>
  end

  # lambda and expressions

  rule lambda_expr
    ('(' spacing var_name spacing '|' spacing expression spacing ')')
    <Qrb::Syntax::LambdaExpr>
  end

  rule expression
    (
        ('(' spacing expression spacing ')')
      | (![\(,\)] .)+ expression?
    )
    <Qrb::Syntax::Expression>
  end

  # lexer

  rule var_name
    /[a-z]+/
  end

  rule contract_name
    /[a-z][a-z0-9]*/
  end

  rule constraint_name
    /[a-z][a-z_]*/
  end

  rule attribute_name
    /[a-z][a-zA-Z0-9_]*/
  end

  rule type_name
    /[A-Z][a-zA-Z]+/
  end

  rule builtin_type_name
    /[a-zA-Z0-9:]/+
  end

  rule spacing
    (spaces | comment)*
  end

  rule comment
    '#' (![\n] .)* [\n]?
  end

  rule spaces
    /[ \t\n]+/
  end

  rule eof
    !.
  end

end