Is a declaration an expression in SML?

Question

In SML, is a declaration (val-declaration, type declaration, ...)

• an expression
• a statement which, if I am correct, is defined as an expression with side effect
• or something else?

Answer 1

A declaration is just that, a declaration, its own syntactic class. The only way to embed into an expression is via the expression form let dec in exp end.

Technically, there are no statements in ML.