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Prev: Overview
Next: Classes

Section 3: Grammar

This file is automatically generated. If you wish to submit a PR, do not edit this file directly. Please edit templates/rfc/grammar.md instead. Use bin/generate_rfc.pl to regenerate the RFCs.

To make this more manageable and not define a grammar for all of Perl, we will break the grammar out into separate components for simplicity.

Note that due to the adoption of the KIM syntax (keyword, identifier, modifier), we only introduce four new keywords to the Perl language:

  • class
  • role
  • field
  • method

3.1 Class and Role Grammar

The primary grammar looks like:

Corinna        ::= CLASS | ROLE
CLASS          ::= 'class' NAMESPACE DECLARATION? BLOCK
ROLE           ::= 'role' NAMESPACE ROLES? BLOCK
NAMESPACE      ::= IDENTIFIER { '::' IDENTIFIER }
DECLARATION    ::= ':abstract'? PARENT? ROLES? VERSION?
PARENT         ::= ':isa(' NAMESPACE ')'
ROLES          ::= ':does(' NAMESPACE { ',' NAMESPACE } ','? ')'
IDENTIFIER     ::= [_:alpha:] {[_:alnum:]}
VERSION        ::= ':version(' VERSION_NUMBER ')
VERSION_NUMBER ::= # all allowed Perl version numbers
BLOCK          ::= # Perl +/- Extras

We recommend semantic versioning, but we allow all existing Perl version formats to facilitate upgrading existing modules.

3.2 Method Grammar

The method grammar (skipping some bits to avoid defining a grammar for Perl):

METHOD        ::= 'method' ACCESS_LEVELS SIGNATURE '{' (perl code) '}'
SIGNATURE     ::= IDENTIFIER '(' current sub argument structure + extra work from Dave Mitchell ')'
ACCESS_LEVELS ::= ACCESS_LEVEL { ACCESS_LEVEL }
ACCESS_LEVEL  ::= ':' ( 'private' | 'overrides' | 'common' )
SIGNATURE     ::= # currently allowed Perl signatures

3.3 Field Grammar

"Fields" in Corinna parlance are the variables where class and instance data are stored.

For simplicity: SCALAR, ARRAY, and HASH refer to their corresponding variable names. PERL_EXPRESSION means what it says. IDENTIFIER is a valid Perl identifier.

FIELD            ::= 'field' ( 
                              SCALAR ATTRIBUTES? DEFAULT?
                            | ( ARRAY | HASH ) ':common'? DEFAULT?  # only the :common attribute is
                                                                    # currently supported for array/hash fields
                     )
DEFAULT          ::= '{' PERL_EXPRESSION '}'
ATTRIBUTES       ::= { ATTRIBUTE }
ATTRIBUTE        ::= ':' (
                              'param'     NAME?   # allowed in constructor
                            | 'name'      NAME?   # alternate name (defaults to field name minus the sigil)
                            | 'reader'    NAME?   # $field method to read the field
                            | 'writer'    NAME?   # set_$field method to write the field
                            | 'predicate' NAME?   # has_$field method to test if field is defined
                            | 'common'            # identifies field as class method
                            | HANDLES
                     )
HANDLES          ::= 'handles' '('
                                    IDENTIFIER { ',' IDENTIFIER }    # list of methods this field handles
                                 |  PAIR       { ',' PAIR }          # map of methods (to, from) this field handles
                                 | '*'                               # this field handles all unknown methods, but inheritance takes precedence
                     ')'
PAIR             ::= IDENTIFIER  ':' IDENTIFIER
NAME             ::= '(' IDENTIFIER ')'

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