grammar Go::Grammar;

token TOP {
#    ^ <binary_op> $
#    ^ <block>
#    ^ <statement>
#    ^ <top_level_decl>
    ^ <source_file>
#    $
}

token ws {
	[<[\ \t\r\n]>]*
}

## this is a rule so whitespace is added around it
token com {
	<.ws>? ',' <.ws>?
}

token semi {
	<.ws>? ';' <.ws>?
}
#	| <?before <.ws>? ')' <.ws>?>
#	| <?before <.ws>? '}' <.ws>?>

token automatic_semicolon {
	[ [<?after <.identifier> >
	| <?after <.basic_lit> >
	| <?after 'break'>
	| <?after 'continue'>
	| <?after 'fallthrough'>
	| <?after 'return'>
	| <?after '++'>
	| <?after '--'>
	| <?after ')'>
	| <?after ']'>
	| <?after '}'>
	] $$ ]
	| <?before ')'>
	| <?before '}'>
}

######################################################################
## Lexical elements

#### Characters

regex unicode_letter {
	<.alpha>
}

regex unicode_digit {
	<.digit>
}

#### Letters and digits

regex letter {
	<unicode_letter> | '_'
}

regex decimal_digit {
	<.digit>
}

regex octal_digit {
	<[0..7]>
}

regex hex_digit {
	<.xdigit>
}

#### Comments
#### Semicolons
#### Identifiers

token identifier {
	<.letter> [<.letter> | <.unicode_digit>]*
}

#### Keywords
#### Operators and Delimiters
#### Integer literals

token int_lit {
	| <hex_lit>
	| <octal_lit>
	| <decimal_lit>
}

token decimal_lit {
	<[1..9]> <.decimal_digit>*
}

token octal_lit {
	0 <.octal_digit>*
}

token hex_lit {
	0x <.hex_digit>+
}

#### Floating-point literals

token float_lit {
	| <.decimals> '.' <.decimals>? <exponent>?
	| <.decimals> <exponent>
	| '.' <.decimals> <exponent>?
}

token decimals {
	<.decimal_digit>+
}

token exponent {
	<[eE]> <[+-]>? <.decimals>
}

#### Imaginary literals

token imaginary_lit {
	[<decimals> | <float_lit>] i
}

#### Character literals

token char_lit {
  "'" ~ "'" [ <unicode_value> | <-[\n\']> ]
}

token unicode_value {
	| <byte_value>
	| <little_u_value>
	| <big_u_value>
	| <escaped_char>
}

token byte_value {
	| <octal_byte_value>
	| <hex_byte_value>
}

token octal_byte_value {
	'\\' <.octal_digit> ** 3
}

token hex_byte_value {
	'\\x' <.hex_digit> ** 2
}

token little_u_value {
	'\\u' <.hex_digit> ** 4
}

token big_u_value {
	'\\U' <.hex_digit> ** 8
}

token escaped_char {
	'\\' [ <[abfnrtv]> | '\\' | "'" | '"' ]
}

#### String literals

token string_lit {
	| <raw_string_lit>
	| <interpreted_string_lit>
}

token raw_string_lit {
	'`' ~ '`' [ <-[\`]> ]*
}

token interpreted_string_lit {
	'"' ~ '"' [ <.unicode_value> | <-[\n\"]> ]*
}

######################################################################
## Types

rule type {
	| <type_lit>
	| <type_name>
	| '(' <type> ')'
}

rule type_name {
	<qualified_ident>
}

rule type_lit {
	| <array_type>
	| <struct_type>
	| <pointer_type>
	| <function_type>
	| <interface_type>
	| <slice_type>
	| <map_type>
	| <channel_type>
}

#### Array types

rule array_type {
	'[' <array_length> ']' <element_type>
}

rule array_length {
	<expression>
}

rule element_type {
	<type>
}

#### Slice types

rule slice_type {
	'[' ']' <element_type>
}

#### Struct types

rule struct_type {
	struct '{' (<field_decl> <.semi>)* '}'
}

rule field_decl {
	[<identifier_list> <type> | <anonymous_field>] <tag>?
}

rule anonymous_field {
	'*'? <type_name>
}

rule tag {
	<.string_lit>
}

#### Pointer types

rule pointer_type {
	'*' <base_type>
}

rule base_type {
	<type>
}

#### Function types

rule function_type {
	func <signature>
}

rule signature {
	<parameters> <result>?
}

rule result {
	<parameters> | <type>
}

rule parameters {
	'(' <parameter_list>? ')'
}

rule parameter_list {
	<parameter_decl>+ % <.com>
}

rule parameter_decl {
	<identifier_list>? '...'? <type>?
}

#### Interface types

rule interface_type {
	interface '{' (<method_spec> <.semi>)* '}'
}

rule method_spec {
	| <method_name> <signature>
	| <interface_type_name>
}

rule method_name {
	<identifier>
}

rule interface_type_name {
	<type_name>
}

#### Map types

rule map_type {
	map '[' <key_type> ']' <element_type>
}

rule key_type {
	<type>
}

#### Channel types

rule channel_type {
	[
	| chan '<-'?
	| '<-' chan
	] <element_type>
}

#### Blocks
rule block {
	'{' (<statement> <.semi>)* '}'
}

######################################################################
## Declarations and scope

rule declaration {
	| <const_decl>
	| <type_decl>
	| <var_decl>
}

rule top_level_decl {
	| <declaration>
	| <function_decl>
	| <method_decl>
}

#### Constant declarations

rule const_decl {
	const [<const_spec> | '(' (<const_spec> <.semi>)* ')']
}

rule const_spec {
	<identifier_list> [<type>? '=' <expression_list>]
}

rule identifier_list {
	<identifier>+ % <.com>
}

rule expression_list {
	<expression>+ % <.com>
}

#### Type declarations

rule type_decl {
	type [<type_spec> | '(' (<type_spec> <.semi>)* ')']
}

rule type_spec {
	<identifier> <type>
}

#### Variable declarations

rule var_decl {
	var [<var_spec> | '(' (<var_spec> <.semi>)* ')']
}

rule var_spec {
	<identifier_list> <var_expression_list>
}

rule var_expression_list {
	| '=' <expression_list>
	| <type> ['=' <expression_list>]?
}

#### Short variable declarations

rule short_var_decl {
	<identifier_list> ':=' <expression_list>
}

#### Function declarations

rule function_decl {
	func <function_name> <signature> <body>?
}

rule function_name {
	<identifier>
}

rule body {
	<block>
}

#### Method declarations

rule method_decl {
	func <receiver> <method_name> <signature> <body>?
}

rule receiver {
	'(' <identifier>? '*'? <base_type_name> ')'
}

rule base_type_name {
	<identifier>
}

######################################################################
## Expressions

#### Operands

rule operand {
	| <literal>
	| <qualified_ident>
	| <method_expr>
	| '(' <expression> ')'
}

rule literal {
	| <basic_lit>
	| <composite_lit>
	| <function_lit>
}

rule basic_lit {
	| <int_lit>
	| <float_lit>
	| <imaginary_lit>
	| <char_lit>
	| <string_lit>
}

#### Qualified identifiers

rule qualified_ident {
	| <package_name> '.' <identifier>
	| <identifier>
}

#### Composite literals

rule composite_lit { <literal_type> <!block> <literal_value> }

rule literal_type {
	| <struct_type>
	| <array_type>
	| '[...]' <element_type>
	| <slice_type>
	| <map_type>
	| <type_name>
}

rule literal_value { '{' (<element>* % <.com>) <.com>? '}' }
rule element       { [<key> ':']? <value> }
rule key           { <field_name> | <element_index> }
rule field_name    { <identifier> }
rule element_index { <expression> }
rule value         { <expression> | <literal_value> }

#### Function literals

rule function_lit {
	<function_type> <body>
}

#### Primary expressions

rule primary_expr {
	<primary_subexpr> <secondary_expr>*
}

rule primary_subexpr {
	| <builtin_call>
	| <operand>
	| <conversion>
}

rule secondary_expr {
	| <type_assertion>
	| <selector>
	| <index>
	| <slice>
	| <call>
}

#### Selectors

rule selector {
	'.' <identifier>
}

#### Indexes

rule index {
	'[' <expression> ']'
}

#### Slices

rule slice {
	'[' <expression>? ':' <expression>? ']'
}

#### Type assertions

rule type_assertion {
	'.' '(' <type> ')'
}

#### Calls

rule call {
	'(' (<argument_list> <.com>?)? ')'
}

rule argument_list {
	<expression_list> '...'?
}

#### Operators

# TODO
rule expression {
#	| <unary_expr>
#	| <binary_expr>
	| <unary_expr> (<binary_op> <unary_expr>)*
}

#rule binary_expr {
#	<unary_expr> <binary_op> <expression>
#	<expression> <binary_op> <unary_expr>
#}

rule unary_expr {
	| <primary_expr>
	| <unary_op> <unary_expr>
}

#### Operator precedence

rule binary_op {
	| '||'
	| '&&'
	| <mul_op>
	| <add_op>
	| <rel_op>
}

# TODO: when there are no bugs, rewrite these rules to be 
# more like add_op, which is more idiomatic, so they say.
# BUG: <https://rt.perl.org/rt3/Public/Bug/Display.html?id=113590>

proto token rel_op {*}
token rel_op:sym<eq> { '==' }
token rel_op:sym<ne> { '!=' }
token rel_op:sym<lt> { '<' }
token rel_op:sym<le> { '<=' }
token rel_op:sym<gt> { '>' }
token rel_op:sym<ge> { '>=' }

proto token add_op {*}
token add_op:sym<+> { <sym> }
token add_op:sym<-> { <sym> }
token add_op:sym<|> { <sym> }
token add_op:sym<^> { <sym> }

proto token mul_op {*}
token mul_op:sym<*> { <sym> }
token mul_op:sym</> { <sym> }
token mul_op:sym<%> { <sym> }
token mul_op:sym<shl> { '<<' }
token mul_op:sym<shr> { '>>' }
token mul_op:sym<&> { <sym> }
token mul_op:sym<&^> { <sym> }

proto token unary_op {*}
token unary_op:sym<+> { <sym> }
token unary_op:sym<-> { <sym> }
token unary_op:sym<!> { <sym> }
token unary_op:sym<^> { <sym> }
token unary_op:sym<*> { <sym> }
token unary_op:sym<&> { <sym> }
token unary_op:sym<to> { '<-' }

#### Method expressions

rule method_expr {
	<receiver_type> '.' <method_name>
}

rule receiver_type {
	| <type_name>
	| '(' '*' <type_name> ')'
}

#### Conversions

rule conversion {
	<type> '(' <expression> ')'
}

######################################################################
## Statements

##rule statement_list { <statement>* % <.semi> }

rule statement {
	| <block>
	| <if_stmt>
	| <declaration>
	| <keyword_stmt>
	| <simple_stmt>
}

# BAD: This rule is nonstandard.
# <simple_stmt> is not supposed to match <labeled_stmt>, 
# but I don't see a way around this right now.
# This shouldn't cause problems, though, because this
# is more liberal than the standard Go parser.

rule simple_stmt {
	| <short_var_decl>
	| <labeled_stmt>
	| <assignment>
	| <incdec_stmt>
	| <send_stmt>
	| <expression_stmt>
	| <?>
}

# <keyword_stmt> is not in the Go spec
proto rule keyword_stmt {*}

#### Empty statements (handled above?)

#### Labeled statements

rule labeled_stmt { <label> ':' <statement> }
rule label { <identifier> }

#### Expression statements

rule expression_stmt { <expression> }

#### Send statements

rule send_stmt { <channel> '<-' <expression> }
rule channel { <expression> }

#### IncDec statements

rule incdec_stmt {
	| <inc_stmt>
	| <dec_stmt>
}

rule inc_stmt { <expression> '++' }
rule dec_stmt { <expression> '--' }

#### Assignments

rule assignment {
	<expression_list> <assign_op> <expression_list>
}

token assign_op {
	[ <add_op> | <mul_op> ]? '='
}

#### If statements

proto rule if_stmt {*}
rule if_stmt:sym<if> {
	<sym> <opt_simple_stmt> <expression> <block>
	<else_stmt>?
}

proto rule else_stmt {*}
rule else_stmt:sym<else> {
	<sym> [ <if_stmt> | <block> ]
}

rule opt_simple_stmt {
	[ [ <simple_stmt> | <?> ] <.semi> ]?
}

#### Switch statements
rule keyword_stmt:sym<switch> { <sym> <opt_simple_stmt> [ <type_switch> | <expr_switch> ] }

proto rule expr_case {*}
rule expr_case:sym<case> { <sym> <expression_list> }
rule expr_case:sym<default> { <sym> }
rule expr_clause { <exprcase> ':' <statement_list>* }
rule expr_switch {
	<expression>? '{' <expr_clause> '}'
}

proto rule type_case {*}
rule type_case:sym<case> { <sym> <type_list> }
rule type_case:sym<default> { <sym> }
rule type_clause { <type_case> ':' <statement_list>* }
rule type_guard { [ <identifier> ':=' ]? <primary_expr> '.(type)' }
rule type_list { <type>+ % <.com> }
rule type_switch {
	<type_guard> "{" { <type_clause> } "}"
}

#### Select statements
rule keyword_stmt:sym<select> { <sym> <comm_select> }

proto rule comm_case {*}
rule comm_case:sym<case> { <sym> [ <send_stmt> | <recv_stmt> ] }
rule comm_case:sym<default> { <sym> }
rule expr_assign { <expression> (',' <expression>)? [ '=' | ':=' ]}
rule recv_expr { <expression> }
rule recv_stmt { <expr_assign>? <recv_expr> }
rule comm_clause { <comm_case> ':' <statement_list> }
rule comm_select {
	'{' <comm_clause>* '}'
}

#### For statements
rule keyword_stmt:sym<for> { <sym> <for_clauses>? <block> }

rule for_clauses {
	| <for_clause>
	| <range_clause>
	| <condition>
}

rule condition { <expression> }
rule init_stmt { [ <simple_stmt> | <?> ] }
rule post_stmt { [ <simple_stmt> | <?> ] }
rule for_clause { <init_stmt>? ';' <condition>? ';' <post_stmt>? }
rule range_clause { <expr_assign> 'range' <expression> }

#### Go statements
rule keyword_stmt:sym<go> { <sym> <expression> }
#### Return statements
rule keyword_stmt:sym<return> { <sym> <expression_list>? }
#### Break statements
rule keyword_stmt:sym<break> { <sym> <label>? }
#### Continue statements
rule keyword_stmt:sym<continue> { <sym> <label>? }
#### Goto statements
rule keyword_stmt:sym<goto> { <sym> <label> }
#### Fallthrough statements
rule keyword_stmt:sym<fallthrough> { <sym> }
#### Defer statements
rule keyword_stmt:sym<defer> { <sym> <expression> }

#### Built-in functions

rule builtin_call {
	<builtin_id> '(' (<builtin_args>* % <.com>) <.com>? ')'
}

rule builtin_args {
	<type> (',' <expression_list>)?
}
#	| <expression_list>

token builtin_id {
	| make
	| new
}

######################################################################
## Packages

#### Source file organization

rule source_file {
	<package_clause> <.semi>
	(<import_decl> <.semi>)*
	(<top_level_decl> <.semi>)*
}

rule top_level_decls {
	[<top_level_decl> <.semi>]*
}

#### Package clause
rule package_clause {
	package <package_name>
}

rule package_name {
	<identifier>
}

#### Import declarations

rule import_decls {
	[<import_decl> <.semi>]*
}

rule import_decl {
	import <import_specs>
}

rule import_specs {
	| <import_spec>
	| '(' [<import_spec> <.semi>]* ')'
}

rule import_spec {
	['.' | <package_name>]? <import_path>
}

rule import_path {
	<.string_lit>
}

#rule method_expr {
#	<receiver_type> '.' <method_name>
#}
#
#rule receiver_type {
#	<type_name> | [ '(' '*' <type_name> ')' ]
#}
#
#rule conversion {
#	<type> '(' <expression> ')'
#}
#