Hack: use 'i(' as COMPLEX_SYM and change ComplexLit to ComplexExpr
Change <# to <|   more consistent with quantum convention |xxx>
Let's follow the convention and call ComplexLit again
Make all *_LITERAL have type string
Complete gen_expr_list
No need for () in concatenation
Use 'not' instead of exclamation, just like 'and', 'or'
+=, -=, *=, /= not present in parser
Complete a crude generator