[lispm]

One writes in a hierarchical data structure: s-expressions. Since Lisp has built-in macro expressions, on top of s-expressions, one can represent code independent from 'ASTs' and make it executable:

For example the LOOP macro introduces a non-prefix syntax:

  (loop
        for i below 100
        for j = (random 100)

        sum j into s

        while (< s 1000)

        finally (return i))

This is actually pretty powerful and high-level (the user being able to extend or change the syntax in complex ways in portions of a program). The LOOP implementation as a macro is actually an integrated sublanguage and the user can add arbitrary (and even extensible) complex macros like that...

Generally Lisp is low to mid level as a programming language, with a bunch of features which can be considered high-level: extensive macro system, Common Lisp Object System, extensive error handling, ...

[jnbiche]

> Generally Lisp is low to mid level as a programming language,

I believe that no programming language with automatic memory management can be considered "low-level".

That aside, why would you call Lisp "low- to mid-level"? Commonly-used implementations are at about the same level of abstraction as Ruby or Python.

[lispm]

> I believe that no programming language with automatic memory management can be considered "low-level".

That's a view of a whole language and its implementation. Still it may have a range of features which are low level.

Lisp for example has Foreign Function Interfaces (FFI) with low-level interfaces and manual memory management.

Example: http://www.sbcl.org/manual/#Foreign-Function-Interface

Basic Lisp stuff like CAR and CDR were (almost) instructions on a CPU ( https://en.wikipedia.org/wiki/CAR_and_CDR ).

Something like a cons cell (the building block for lists) is basically a two-element vector. Lists were made by chaining them together via a CONS operator, which creates such a two-element vector.

Such a linked list data structure is pretty low-level and the typical mark&sweep GC of the early days is also relatively basic.

There is not much magic to it.

Many other programming languages have much more complex basic data structures (see object-oriented programming in Java with classes and instances, inheritance, interfaces, namespaces, ...). Compared to that the basic linked list in Lisp is primitive.

> I believe that no programming language with automatic memory management can be considered "low-level".

See the standards for Scheme or Common Lisp. There is not a word about automatic memory management in the specifications. Automatic memory management is a feature of an implementation, just like foreign function interfaces. Most implementations have a kind of garbage collector. But most implementations also have manual memory management.

People even write operating systems in Lisp sometimes: https://github.com/froggey/Mezzano

[tripzilch]

Sounds like lisp is doing the low level stuff for you, so really like a mid/high level language. Most languages have statements that correspond to a single cpu instruction. And it sounds like this cons cell is in fact an abstraction away from bytes and memory. Which is more of an abstraction than, say, a byte string.