@node Language Specification
@chapter Specification

@section Introduction

This document specifies the semantics and behavior of the O Programming
Language for compiler designers be informed how the language is designed.

This specification is a DRAFT and will be the discussions drive over olang-dev
mailing list.

@section Language Syntax

This is the O Programming Language EBNF grammar specification[^1]

[^1]: EBNF variant https://github.com/Engelberg/instaparse/tree/v1.4.12 and live
      test can be accessed here https://mdkrajnak.github.io/ebnftest/

NOTE: This grammar spec is a DRAFT and it covers only a small portion of the
language.

@verbatim
(* Entry Point *)
<translation-unit>     ::= (<ows> <external-declaration> <ows> (<end-of-statement> | <end-of-file>))*

(* Translation Unit *)
<external-declaration> ::= <common-statement> | <function-definition>

(* Variables *)
<variable-definition>   ::= 'var' <ws> <variable-name> <ows> ':' <ows> <type> <ows> <variable-initializer>?
<constant-definition>   ::= 'const' <ws> <variable-name> <ows> ':' <ows> <type> <ows> <variable-initializer>
<variable-name>         ::= <identifier>
<variable-initializer>  ::= '=' <ows> <expression>

(* Functions *)
<function-definition> ::= 'fn' <ws> <function-name> <ows> '(' ( <ows> | <ows> <function-params> <ows> ) ')' <ows> ':' <ows> <return-type> <ows> <function-body>
<function-name>       ::= <identifier>
<function-params>     ::= <identifier> <ows> ':' <ows> <type> ( <ows> ',' <function-params>)*
<return-type>         ::= <type>
<function-body>       ::= <block>
<block>               ::= '{' <ows> <statement> <ows> (<end-of-statement> <ows> <statement> <ows>)* <end-of-statement>? <ows> '}'
<function-args>       ::= <expression> (<ows> ',' <function-args>)*
<function-call>       ::= <function-name> <ows> '(' ( <ows> | <ows> <function-args> <ows> ) ')'
<statement>           ::= <common-statement> | <if-statement> | <while-statement> | <return-statement> | <function-call>
<if-statement>        ::= 'if' <ws> <expression> <ows> <block> ( <ows> 'else' ( <ows> <block> | <ows> <if-statement> ) )?
<while-statement>     ::= 'while' <ws> <expression> <ows> <block>
<return-statement>    ::= 'return' <ws> <expression>

(* Statements *)
<end-of-statement>    ::= ';' | <line-break>
<common-statement>    ::= <variable-definition> | <constant-definition>
<assignment-operator> ::= '='
                        | '*='
                        | '/='
                        | '%='
                        | '+='
                        | '-='
                        | '<<='
                        | '>>='
                        | '&='
                        | '^='
                        | '|='

(* Expressions *)
<expression> ::= <binary-expression>
<binary-expression> ::= <logical-or-expression>
<logical-or-expression> ::= <logical-and-expression> (<ows> '||' <ows> <logical-and-expression>)*
<logical-and-expression> ::= <bitwise-or-expression> (<ows> '&&' <ows> <bitwise-or-expression>)*
<bitwise-or-expression> ::= <bitwise-xor-expression> (<ows> '|' <ows> <bitwise-xor-expression>)*
<bitwise-xor-expression> ::= <bitwise-and-expression> (<ows> '^' <ows> <bitwise-and-expression>)*
<bitwise-and-expression> ::= <cmp-equality-expression> (<ows> '&' <ows> <cmp-equality-expression>)*
<cmp-equality-expression> ::= <cmp-relational-expression> (<ows> ('==' | '!=') <ows> <cmp-relational-expression>)*
<cmp-relational-expression> ::= <bitwise-shift-expression> (<ows> ('<' | '>' | '<=' | '>=') <ows> <bitwise-shift-expression>)*
<bitwise-shift-expression> ::= <additive-expression> (<ows> ('<<' | '>>') <ows> <additive-expression>)*
<additive-expression> ::= <multiplicative-expression> (<ows> ('+' | '-') <ows> <multiplicative-expression>)*
<multiplicative-expression> ::= <assignment-expression> (<ows> ('*' | '/' | '%') <ows> <assignment-expression>)*
<assignment-expression> ::= <primary-expression> (<ows> <assignment-operator> <ows> <primary-expression>)*
<primary-expression> ::= <integer-literal>
                       | <variable-name>
                       | <function-call>
                       | <unary-expression>
                       | '(' <ows>  <expression> <ows> ')'

<unary-expression> ::= <unary-operator> <ows> <primary-expression>
<unary-operator> ::= '&'
                   | '*'
                   | '+'
                   | '-'
                   | '~'
                   | '!'

(* Identifiers *)
<type>                ::= 'u32'
<identifier>          ::= (<alpha> | '_') (<alpha> | <digit> | '_')*

(* Literals *)
<integer-literal>     ::= <integer-base10> | <integer-base16>
<integer-base10>      ::= #'[1-9]' (<digit> | '_')* | '0'
<integer-base16>      ::= #'0[Xx]' <hex-digit> (<hex-digit> | '_')*

(* Utilities *)
<ws>                  ::= <white-space>+
<ows>                 ::= <white-space>*
<white-space>         ::= <linear-space> | <line-break>
<line-break>          ::= #'[\n\v\f\r]' | '\r\n'
<linear-space>        ::= #'[ \t]'
<alpha>               ::= #'[a-zA-Z]'
<digit>               ::= #'[0-9]'
<hex-digit>           ::= <digit> | #'[a-fA-F]'
<end-of-file>         ::= #'$'
@end verbatim