Nested datatype values should be printed with parentheses

[julianhyde]

Morel prints nested datatype values incorrectly.

The current output:

SOME (SOME 1);
> val it = SOME SOME 1 : int option option

is incorrect. sml-nj correctly uses parentheses:

Standard ML of New Jersey [Version 110.99.7; 64-bit; December 28, 2024]
- SOME (SOME 1);
val it = SOME (SOME 1) : int option option

[tanclary]

looking into this !

[julianhyde]

We should also check

= SOME [SOME (SOME 1), NONE];
val it = SOME [SOME (SOME 1),NONE] : int option option list option

[tanclary]

We should also check

= SOME [SOME (SOME 1), NONE];
val it = SOME [SOME (SOME 1),NONE] : int option option list option

Ack, added

[julianhyde]

Your change works, but I was hoping there was a fix that uses left- and right-precedence. SOME SOME 1 is the wrong thing yo output because it's basically a chain of function applications. (A datatype constructor like SOME is syntactically a function.) Morel's function applications (like Standard ML) are left-associative, so "f g x" means "(f g) x" and if you want "f (g x)" you have to write parentheses.

Note how pretty_type uses Op::APPLY (type application, e.g. int list applies the list type to the int argument), which has left precedence 16 and right precedence 17. So we insert parens because the pull from the right is stronger than the pull from the left.

The function application operator, and its precedence, should come into play here.