Scoping: Symbols belong to "contexts" (namespaces). You get lexical scope using With and Module, and dynamic scope with Block. The variables in Module are replaced with a uniquely named temporary symbol (removed when all references go away), so they can be returned from the Module expression and acted upon (though they'll appear ugly).
Data structures: you have special syntax for lists and "associations" (dictionaries/maps/hashtables). Those are immutable objects, but in at least some cases the implementation has an optimization where it'll directly mutate the object if there is only one reference to it. There are other data structures with no special syntax in the language, for example numeric and sparse arrays. A number of mutable data structures have also been recently introduced: https://reference.wolfram.com/language/guide/DataStructures....
One thing that you might expect to be a special data structure but actually isn't are "pure functions" (anonymous functions). There are actually just the unevaluated expression, so you could programmatically inspect the body if you so wanted to.
Deferred values: You can apply the HoldFirst/HoldRest/HoldAll/HoldAllComplete attributes so during evaluation they receive the corresponding arguments unevaluated. You might think this would make metaprogramming be easy, but it's actually tricky because of the "infinite evaluation" (it keeps evaluating until a fixed point is reached) of the language.
Derivatives: It's a term rewriting language, so you just provide the rewrite rules like you would with any other user function. f /: D[f[x_]] := x^2 will define the derivative of f(x) to be x^2, and associates that definition with f so that rule won't have to be checked for all usages of D (this also saves you from having to unprotect D to add the rule).
Data structures: you have special syntax for lists and "associations" (dictionaries/maps/hashtables). Those are immutable objects, but in at least some cases the implementation has an optimization where it'll directly mutate the object if there is only one reference to it. There are other data structures with no special syntax in the language, for example numeric and sparse arrays. A number of mutable data structures have also been recently introduced: https://reference.wolfram.com/language/guide/DataStructures....
One thing that you might expect to be a special data structure but actually isn't are "pure functions" (anonymous functions). There are actually just the unevaluated expression, so you could programmatically inspect the body if you so wanted to.
Deferred values: You can apply the HoldFirst/HoldRest/HoldAll/HoldAllComplete attributes so during evaluation they receive the corresponding arguments unevaluated. You might think this would make metaprogramming be easy, but it's actually tricky because of the "infinite evaluation" (it keeps evaluating until a fixed point is reached) of the language.
Derivatives: It's a term rewriting language, so you just provide the rewrite rules like you would with any other user function. f /: D[f[x_]] := x^2 will define the derivative of f(x) to be x^2, and associates that definition with f so that rule won't have to be checked for all usages of D (this also saves you from having to unprotect D to add the rule).