difference between Meta.quot, Expr(:quote), and QuoteNode

[vtjnash]

There now seem to be three ways of generating quoted symbols for the AST. However, print_unquoted doesn't seem to know about Expr(:quote). But on the whole, what is the difference between them, and can we deprecated Meta.quot and Expr(:quote)?

[JeffBezanson]

Meta.quot(x) just calls Expr(:quote, x). It's a shorthand.
QuoteNode is only used in the internal AST representation, not by macros. It's safe to ignore unless you work on later stages of the compiler.

[vtjnash]

But what is the difference, since now QuoteNode can be constructed directly? It seems like Expr(:quote) is redundant and thus unnecessary.

Perhaps the bug is just in print-ing the output of the AST, since quotes symbols in QuoteNode, but not in Expr(:quote)

[JeffBezanson]

There is actually a difference in behavior come to think of it. QuoteNode is very primitive and only includes a literal value in an AST. When QuoteNode(x) is evaluated, the result is just x, the value stored inside the QuoteNode. A quote expression does $ substitution.

But they should probably print the same. There is probably a bug in show.

[toivoh]

Then probably Meta.quot should be changed to produce a QuoteNode. The
intended usage is to safely quote values into the AST. Having written a lot
of code that uses it, I still believe that the shorthand is useful.

[vtjnash]

It's the same number of characters (which makes replace easy), so I would vote for removing Meta.quot

[JeffBezanson]

The idea was that for heavy metaprogramming you'd do using Base.Meta.