If it were trivial you'd see LINQ-like providers implemented in "practically every high level language".
Source code of the function means you have to implement the parser/lexer to convert it into a usable AST which is bad for both runtime performance and library size.
Very much doubt this is available in Java, which Java ORM lets you use native Java language expression syntax to query a database?
You're replying to a thread about what it takes to implement a LINQ provider, which was dismissed as every high level language implements it with iterables, then proceed to give non-equivalent examples.
IQueryable<> manipulation has other tools available to it than brute-force iteration, like streams do. Streams may be the closest thing java has, but it's still a fundamentally different thing.
Source code of the function means you have to implement the parser/lexer to convert it into a usable AST which is bad for both runtime performance and library size.
Very much doubt this is available in Java, which Java ORM lets you use native Java language expression syntax to query a database?