PROG ::= INSTR*
INSTR ::=
| DIR
| EXPR semicolon
| FUNDECL
| return EXPR semicolon
| EXTERN semicolon
EXTERN ::= extern fun ident opar PARAMS cpar RET
FUNDECL ::= fun ident opar PARAMS cpar RET BLOCK
PARAMS ::= (ident type? (comma ident type?)*)
RET ::= type?
BLOCK ::= obrace INSTR* cbrace

DIR ::= hash ident EXPR

EXPR ::=
| ADDSUB


ADDSUB ::= MULDIVMOD ((add|sub) MULDIVMOD)*
MULDIVMOD ::= LITERAL ((mul|div|mod) LITERAL)*

LITERAL ::=
| ident
| int
| CALL

CALL ::= ident opar ARGS cpar
ARGS ::= (EXPR (comma EXPR)*)?