MOD ::= EXPR*
EXPR ::=
| ASSERT
| VARDECL
| VARSET
| SCOPE
| IF
| OR
ASSERT ::= assert EXPR
VARDECL ::= let ident assign EXPR
VARSET ::= ident assign EXPR
BLOCK ::= EXPR*
SCOPE ::= begin BLOCK end
IF ::= if EXPR then BLOCK (else BLOCK | IF)? end
OR ::= AND (or AND)*
AND ::= EQNE (and EQNE)*
EQNE ::=
| CMP
| CMP eq CMP
| CMP ne CMP
CMP ::= TERM ((lt | le | ge | gt) TERM)?
TERM ::= FACTOR ((add | sub) FACTOR)*
FACTOR ::= POWER ((mul | div | mod) POWER)*
POWER ::= UNARY (pow UNARY)?
UNARY ::= sub? GROUP | not? GROUP
GROUP ::= BUILTIN | opar EXPR cpar
BUILTIN ::= num | bool | str | ident