MiniMoonBit.g4

grammar MiniMoonBit;

prog: top_level* EOF;

// Top-level
// 
// Top level declarations should start at the beginning of the line, i.e.
// token.column == 0. Since this is non-context-free, it is not included in this
// backend-agnostic ANTLR grammar.
top_level: top_let_decl | toplevel_fn_decl;
top_let_decl:
	'let' IDENTIFIER ':' type '=' expr ';';
toplevel_fn_decl: (main_fn_decl | top_fn_decl) ';';

// Function declarations
// 
// `fn main` and `fn init` does not accept parameters and return type
main_fn_decl: 'fn' ('main' | 'init') fn_body;

top_fn_decl:
	'fn' IDENTIFIER '(' param_list? ')' '->' type fn_body;
param_list: param (',' param)*;
param: IDENTIFIER type_annotation;
fn_body: '{' stmt '}';

nontop_fn_decl:
	'fn' IDENTIFIER '(' nontop_param_list? ')' (
		'->' type
	)? fn_body;
nontop_param_list:
	nontop_param (',' nontop_param)*;
nontop_param: IDENTIFIER type_annotation?;

// Statements
stmt:
	let_tuple_stmt
	| let_stmt
	| fn_decl_stmt
	| assign_stmt
	| expr_stmt;

let_tuple_stmt:
	'let' '(' IDENTIFIER (',' IDENTIFIER)* ')' type_annotation? '=' expr ';'
		stmt;
let_stmt:
	'let' IDENTIFIER type_annotation? '=' expr ';' stmt;
type_annotation: COLON type;

fn_decl_stmt: nontop_fn_decl ';' stmt;

// x[y] = z;
assign_stmt: get_expr '=' expr ';' stmt;
get_expr: get_or_apply_level_expr '[' expr ']';

expr_stmt: expr;

// Expressions, in order of precedence.
expr: // not associative
	add_sub_level_expr '==' add_sub_level_expr
	| add_sub_level_expr '<=' add_sub_level_expr
	| add_sub_level_expr;

add_sub_level_expr: // left associative
	add_sub_level_expr '+' mul_div_level_expr
	| add_sub_level_expr '-' mul_div_level_expr
	| mul_div_level_expr;

mul_div_level_expr: // left associative
	mul_div_level_expr '*' if_level_expr
	| mul_div_level_expr '/' if_level_expr
	| if_level_expr;

if_level_expr: get_or_apply_level_expr | if_expr;
if_expr: 'if' expr block_expr ('else' block_expr)?;

get_or_apply_level_expr:
	value_expr # value_expr_
	// x[y]
	| get_or_apply_level_expr '[' expr ']' # get_expr_
	// f(x, y)
	| get_or_apply_level_expr '(' (expr (',' expr)*)? ')' # apply_expr;

// Value expressions
value_expr:
	unit_expr
	| group_expr
	| tuple_expr
	| bool_expr
	| identifier_expr
	| block_expr
	| neg_expr
	| floating_point_expr
	| int_expr
	| not_expr
	| array_make_expr;
unit_expr: '(' ')'; // ()
group_expr: '(' expr ')'; // (x)
tuple_expr:
	'(' expr (',' expr)+ ')'; // (x, y); 1-tuple is not allowed
block_expr: '{' stmt '}'; // { blah; blah; }
bool_expr: 'true' | 'false';
neg_expr: '-' value_expr;
floating_point_expr: NUMBER '.' NUMBER?; // 1.0 | 1.
int_expr: NUMBER; // 1
not_expr: 'not' '(' expr ')'; // not(x)
array_make_expr:
	'Array' ':' ':' 'make' '(' expr ',' expr ')'; // Array::make(x, y)
identifier_expr: IDENTIFIER;

// Types
type:
	'Unit'
	| 'Bool'
	| 'Int'
	| 'Double'
	| array_type
	| tuple_type
	| function_type;
array_type: 'Array' '[' type ']';
tuple_type: '(' type (',' type)* ')'; // (Int, Bool)
function_type:
	'(' type (',' type)* ')' '->' type; // (Int, Bool) -> Int

// Tokens

TRUE: 'true';
FALSE: 'false';
UNIT: 'Unit';
BOOL: 'Bool';
INT: 'Int';
DOUBLE: 'Double';
ARRAY: 'Array';
NOT: 'not';
IF: 'if';
ELSE: 'else';
FN: 'fn';
LET: 'let';
NUMBER: [0-9]+;
IDENTIFIER: [a-zA-Z_][a-zA-Z0-9_]*;
DOT: '.';
ADD: '+';
SUB: '-';
MUL: '*';
DIV: '/';
ASSIGN: '=';
EQ: '==';
LE: '<=';
LPAREN: '(';
RPAREN: ')';
LBRACKET: '[';
RBRACKET: ']';
LCURLYBRACKET: '{';
RCURLYBRACKET: '}';
ARROW: '->';
COLON: ':';
SEMICOLON: ';';
COMMA: ',';
WS: [ \t\r\n]+ -> skip;
COMMENT: '//' ~[\r\n]* -> skip;