token Fn='fn' Let='let' Return='return' True='true' False='false';
token Arrow='->' LPar='(' RPar=')' Comma=',' Colon=':' LBrace='{' RBrace='}'
      Semi=';' Asn='=' Plus='+' Minus='-' Star='*' Slash='/';
token Name='<name>' Int='<int>';
token Whitespace;

skip Whitespace;

start file;

file: fn*;
fn: 'fn' Name param_list ['->' type_expr] block;
param_list: '(' [param (?1 ',' param)* [',']] ')';
param: Name ':' type_expr;
type_expr: Name;
block: '{' stmt* '}';
stmt:
  stmt_expr
| stmt_let
| block
| stmt_return
;
stmt_expr: expr ';';
stmt_let: 'let' Name '=' expr ';';
stmt_return: 'return' [expr] ';';
expr: expr_bin;
expr_bin:
  expr_bin ('*' | '/') expr_bin
| expr_bin ('+' | '-') expr_bin
| expr_call
;
expr_call:
  expr_call arg_list
| expr_literal
| expr_name
| expr_paren
;
arg_list: '(' [expr (?1 ',' expr)* [',']] ')';
expr_literal: Int | 'true' | 'false';
expr_name: Name;
expr_paren: '(' expr ')';