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by renox 1231 days ago
I think you're wrong if (+ 2 3) means apply the + function with the 2 3 arguments then (Paris Berlin London) means apply the Paris function with the Berlin London arguments..

AFAIK if you want a list either you use (list a b c) or you use '(a b c) which I find less regular than +(1 2) or (1 2) which is equal to list(1 2)
2 comments
simongray 1231 days ago
What it means is entirely contextual.

Often, it will be interpreted to be a function call or a macro invocation in the eval step (the E in REPL).

You can sidestep this behaviour using the ' reader macro (i.e. quote) as you mentioned yourself. Quoting disables this behaviour for the form that the reader macro applies to. Reader macros occur in the R step (i.e. before the E in REPL).

It is a list data structure. There are many examples of lists which are never interpreted as function calls in Lisp, since macros run before evaluation and can change the default behaviour, e.g. in

    (defun increment (x) (+ x 1))
the (x) is not a function invocation, it's a list of named function parameters.
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lispm 1231 days ago
Remember: the specific feature of a typical Lisp is that it is written as s-expressions. S-expressions are a notation for data (similar to XML, JSON, ...). This notation is independently useful for all kinds of purposes - like a list of city names: (paris berlin london).

But the specific feature of Lisp is this: code is data and data can be code. Some use the word homocionic -> the program is written in its own data syntax. S-expressions are the data syntax used by Lisp and the programs are written as s-expressions.

> (+ 2 3) means apply the + function with the 2 3 arguments

Depending on the context (a b c) can have different meanings. As a list it is a list of three items. As a top-level item it is a function call. In (let (a b c) ...) it means a list of variables.

Lisp is based on s-expressions. S-expressions is a simple syntax for data:

an symbolic expression is:

  a symbol: foo, bar, 1, 2 paris, +, -, delta, bear, G1345

  an empty list: NIL or ()

  a non-empty list: ( s-expressionn1 ... s-expression-n)
That's basically it.

Lisp has three functions to work with those: READ, PRINT and EVAL. READ reads a textual s-expression to data, PRINT takes data and prints it as an s-expression, EVAL takes data and evaluates it.

Thus the toplevel of Lisp is something like

  (loop (print (eval (read))))
It reads a Lisp expression in form of an s-expression, evaluates it and prints the result.

> AFAIK if you want a list either you use (list a b c) or you use '(a b c) which I find less regular than +(1 2) or (1 2) which is equal to list(1 2)

(a b c) is a list. It's an s-expression. It is valid data. It's only valid Lisp, if A is an operator.

(quote (a b c)) is also a nested list AND a valid Lisp program.

But READ reads all kinds of nested lists, not just Lisp programs. It does that, because S-expressions are a general data syntax.

Compare that with most other programming languages. Their programs are not written on top of a general data-structure notation like nested lists, nested vectors, nested tables, ...

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