3 ms·

I see. And this led me to a question: what can make a language expressed in S-expressions not a lisp?

wrs 3y ago
Any language can be expressed in S-expressions. A translation of the syntax tree to sexprs is often used in parser debugging. And Lisp doesn’t have to be expressed in S-expressions (see Dylan, or M-expressions, a syntax for Lisp that predates S-expressions). Lisp traditionally has these features, but they’re separate features: * There is a rich syntax for literal data structures * Code is directly exposed as data structures so it can be manipulated with code (macros) * Code is written as literal data structures so it has no separate syntax
- qwerty456127 3y ago
  Thanks. Can you please elaborate some bits on what is meant under "rich syntax for literal data structures"? I'm not a lisp pro, just started studying it.
  - lispm 3y ago
    That's nothing special of Lisp. Literal data structures means that one can write down data objects like list, arrays, vectors, numbers (floats, integers, rational, complex, ...), symbols, strings, characters, records/structures, ... Common Lisp for example: (berlin hamburg munich cologne) ; a list of symbols #(berlin hamburg munich cologne) ; a vector of symbols (1.3 1.3d6 13 #c(1 3) 1/3) ; a list of numbers "Hello World!" ; a string #\H ; the character H #S(CITY :NAME BERLIN ; a structure (aka record) of type CITY :COUNTRY GERMANY) #*1010101111 ; a bitvector #2A((BERLIN GERMANY) ; a 2d array (PARIS FRANCE)) Other programming languages have their own syntax for literal data (even data structures like unicode characters, hash tables, unicode strings, decimal numbers, ...) Common Lisp OTOH has an extensible reader, one can add new syntax extensions for data structures, using so-called reader macros. READ is the function to read s-expressions from text streams. It returns data objects.
- lispm 3y ago
  > Lisp traditionally has these features Lisp has traditionally a two stage syntax 1) S-expressions 2) Lisp S-Expression level has a syntax to describe data: lists, conses, numbers, symbols, strings, arrays, ... Lisp syntax is defined on top of that, as s-expressions: variables, function calls, macro calls, special forms (using quote, let, if, progn, setq, catch, throw, labels, flet, declare, ...), lambda expressions. Each macro also can implement syntax.
- Firadeoclus 3y ago
  > Any language can be expressed in S-expressions. I'm not sure this is true for the C preprocessor, though, where macros can represent partial structure.
buescher 3y ago
People have come up with S-expression syntaxes for C, basically to be able to write C macros in lisp. Here's one: https://voodoo-slide.blogspot.com/2010/01/amplifying-c.html https://voodoo-slide.blogspot.com/2010/01/amplifying-c.html
- kazinator 3y ago
  Couple of others: c-mera: https://github.com/kiselgra/c-mera https://github.com/kiselgra/c-mera cmacro: https://github.com/eudoxia0/cmacro https://github.com/eudoxia0/cmacro (This one one is implemented in Common Lisp for its semantics, but doesn't use a S-exp surface syntax for the code.) sxc: https://github.com/burtonsamograd/sxc https://github.com/burtonsamograd/sxc (incomplete) MetaC: https://github.com/mcallester/MetaC https://github.com/mcallester/MetaC (References Lisp in readme; doesn't use it for implementation or notation, but references ideas. Source code seems to be a core of .c files, and the rest self-hosted in its own .mc language. Somehow provides a REPL.)

wrs 3y ago

Any language can be expressed in S-expressions. A translation of the syntax tree to sexprs is often used in parser debugging. And Lisp doesn’t have to be expressed in S-expressions (see Dylan, or M-expressions, a syntax for Lisp that predates S-expressions). Lisp traditionally has these features, but they’re separate features: * There is a rich syntax for literal data structures * Code is directly exposed as data structures so it can be manipulated with code (macros) * Code is written as literal data structures so it has no separate syntax

qwerty456127 3y ago
Thanks. Can you please elaborate some bits on what is meant under "rich syntax for literal data structures"? I'm not a lisp pro, just started studying it.
- lispm 3y ago
  That's nothing special of Lisp. Literal data structures means that one can write down data objects like list, arrays, vectors, numbers (floats, integers, rational, complex, ...), symbols, strings, characters, records/structures, ... Common Lisp for example: (berlin hamburg munich cologne) ; a list of symbols #(berlin hamburg munich cologne) ; a vector of symbols (1.3 1.3d6 13 #c(1 3) 1/3) ; a list of numbers "Hello World!" ; a string #\H ; the character H #S(CITY :NAME BERLIN ; a structure (aka record) of type CITY :COUNTRY GERMANY) #*1010101111 ; a bitvector #2A((BERLIN GERMANY) ; a 2d array (PARIS FRANCE)) Other programming languages have their own syntax for literal data (even data structures like unicode characters, hash tables, unicode strings, decimal numbers, ...) Common Lisp OTOH has an extensible reader, one can add new syntax extensions for data structures, using so-called reader macros. READ is the function to read s-expressions from text streams. It returns data objects.
lispm 3y ago
> Lisp traditionally has these features Lisp has traditionally a two stage syntax 1) S-expressions 2) Lisp S-Expression level has a syntax to describe data: lists, conses, numbers, symbols, strings, arrays, ... Lisp syntax is defined on top of that, as s-expressions: variables, function calls, macro calls, special forms (using quote, let, if, progn, setq, catch, throw, labels, flet, declare, ...), lambda expressions. Each macro also can implement syntax.
Firadeoclus 3y ago
> Any language can be expressed in S-expressions. I'm not sure this is true for the C preprocessor, though, where macros can represent partial structure.

buescher 3y ago

People have come up with S-expression syntaxes for C, basically to be able to write C macros in lisp. Here's one: https://voodoo-slide.blogspot.com/2010/01/amplifying-c.html https://voodoo-slide.blogspot.com/2010/01/amplifying-c.html

kazinator 3y ago
Couple of others: c-mera: https://github.com/kiselgra/c-mera https://github.com/kiselgra/c-mera cmacro: https://github.com/eudoxia0/cmacro https://github.com/eudoxia0/cmacro (This one one is implemented in Common Lisp for its semantics, but doesn't use a S-exp surface syntax for the code.) sxc: https://github.com/burtonsamograd/sxc https://github.com/burtonsamograd/sxc (incomplete) MetaC: https://github.com/mcallester/MetaC https://github.com/mcallester/MetaC (References Lisp in readme; doesn't use it for implementation or notation, but references ideas. Source code seems to be a core of .c files, and the rest self-hosted in its own .mc language. Somehow provides a REPL.)