anormal revise

[y-tak6]

To test,

1. make .ml file to test in src directory.
2. remove comment out on print_endline (string_of_yul yul_code); in the function backend of src/ocamyul.ml.
3. run dune exec ocamyulc src/<filename>.ml and check the printed code.

new syntax
if expression

• We can use in the right-hand side of let (let x = if ... in ...) and in the last of let-binding sequences (let x = ... in if ...).
• We can use in sequential executions ((if ...); ...), but even if this case we cannot omit else.

Example
if true then SInt 1 + SInt 1 + SInt 1 else let x = SInt 1 in x + x