program		:= __* stmt*

stmt		:= assignment /
		   funcall stop /
		   conditional /
		   loop / 
		   expr stop
		   
expr		:= - _ expr /
 		   expr "+" _ expr /
		   expr "-" - expr /
		   expr "*" _ expr /
		   expr "/" _ expr /
		   "(" _ expr ")" /
		   ['"'] ((!['"'] [_] / #"\""#)*) ['"'] /
		   funcall /
		   fundef /
		   boolean /
		   id /
		   num
		
boolean		:= ("true" / "false") _
id		:= letter (letter / digit / ['?'|'.'|'-'])* _
num		:= (digit+ "."? digit* / "." digit+) _

assignment	:= id "<-" _ expr stop
funcall		:= id "(" _ expr ** ("," _) ")" _
funcdef		:= id? "->" _ block

conditional	:= if __* elif* __* else? __*
if		:= "if" _ expr block
elif		:= "elif" _ expr block
else		:= "else" _ block

loop		:= "loop" _ (until / over / block)
until 		:= "until" _ expr block
over		:= "over"_ id "in" _ expr block

block		:= expr / indented_block
indented_block	:= stop indent __* stmt+ dedent

letter		:= ['A'..='Z'] / ['a'..='z']
digit		:= ['0'..='9']

stop		:= __+ / eof
indent		:= ">>>"
dedent		:= "<<<"

_		:= ['\t'|' ']*
__		:= comment? newline / comment &eof
comment		:= "#" (!newline [_])* &(newline / eof)
newline		:= "\r\n" \ "\r" \ "\n"

eof		:= ![_]