4 ms·

This is not a Lisp syntax error, this is a 'cond' macro syntax error. The language has no syntax, the constructs within the language can and do impose addition

This is not a Lisp syntax error, this is a 'cond' macro syntax error. The language has no syntax, the constructs within the language can and do impose additional restrictions (not extensions - restrictions) when evaluated. You may not find the distinction useful, but it is there.

eru 3y ago
Racket calls it a syntax error. I defer to them on the classification of their errors.
- Zambyte 3y ago
  Neither Racket, nor any Scheme implementation calls (define define) a syntax error in general. It is only an error when define is defined to define, as it is in the base environment. If you have an environment where define does not define, (define define) may work. Welcome to Racket v8.9 [bc]. > (define (define x) (display "Look ma, no error!\n")) > (define define) Look ma, no error!
  - lispm 3y ago
    In Common Lisp the identifiers in package Common Lisp are not allowed to be redefined.
    - Zambyte 3y ago
      It may be semantically invalid in Common Lisp, but it is syntactically valid in Lisp (as seen by observing different dialects).
      - lispm 3y ago
        The term "Lisp" is undefined. Common Lisp is an actual standard for a programming language with a specification. Its core symbols are reserved identifiers. Anyway, if you would be allowed to reimplement a built-in operator, then from then on you would be using the new operator and you would be limited to its syntax. Common Lisp OTOH provides namespaces (called "package") and there is a pre-defined namespace "COMMON-LISP" for the core language.
        Zambyte 3y ago
        > The term "Lisp" is undefined This hasn't been a problem in this thread thus far, but to be explicit, this seems like a good definition: https://en.wikipedia.org/wiki/Lisp_%28programming_language%29 https://en.wikipedia.org/wiki/Lisp_%28programming_language%2... Given that definition, we can see that there are many actual standards for programming languages with specifications under the name "Lisp". Scheme - as was mentioned in this thread, is one such standard, along with Common Lisp. > Anyway, if you would be allowed to reimplement a built-in operator, then from then on you would be using the new operator and you would be limited to its syntax. I think you're arguing the merits of doing something like redefining define here, which is not the subject of this comment chain. Of course such behavior is questionable at best. The comment chain is discussing if such a thing would be valid in Lisp - and, in some dialects (such as Scheme) it is. Scheme also has a feature called "libraries" which makes such behavior more feasible, as you could still have access to the shadowed primitive. Consider: gosh[r7rs.user]$ (import (prefix (scheme base) base:)) gosh[r7rs.user]$ (define (define x) 5) define gosh[r7rs.user]$ (base:define x (+ (define define) (define define))) x gosh[r7rs.user]$ x 10
        lispm 3y ago
        > Scheme - as was mentioned in this thread, is one such standard, along with Common Lisp. Then see the Scheme standards. They include a syntax definition. > The comment chain is discussing if such a thing would be valid in Lisp - and, in some dialects (such as Scheme) it is. Lisp is not a defined language, thus you can assume anything. My point is: Lisp dialects have syntax. This syntax is usually defined on top of s-expressions. S-expressions also have a syntax, but this syntax usually (there are exceptions) describes only data types (lists, conses, numbers, strings, symbols, arrays, records/structures, bit vectors, pathnames, ...) and not the actual programming language with its operators (functions, macros, special operators) & their way to define and invoke them. Example: The LET operator in various Lisp dialects there have a specific syntax. This syntax is not the syntax of simple function calls like (operator arg0 ... args). R7RS small defines this syntax (and also calls it syntax): (let ⟨bindings⟩ ⟨body⟩) (let ⟨variable⟩ (⟨binding spec⟩*) ⟨tail body⟩) ⟨Bindings⟩ has the form ((⟨variable1⟩ ⟨init1⟩) ...) If you write let forms which don't use this syntax, then they are not valid R7RS Scheme let forms, even though they are valid s-expressions.
lispm 3y ago
Check the Common Lisp specification some time. Every language construct has a syntax definition: function calls, macro calls, lambda expressions, special operator calls, ..., every macro.

eru 3y ago

Racket calls it a syntax error. I defer to them on the classification of their errors.

Zambyte 3y ago
Neither Racket, nor any Scheme implementation calls (define define) a syntax error in general. It is only an error when define is defined to define, as it is in the base environment. If you have an environment where define does not define, (define define) may work. Welcome to Racket v8.9 [bc]. > (define (define x) (display "Look ma, no error!\n")) > (define define) Look ma, no error!
- lispm 3y ago
  In Common Lisp the identifiers in package Common Lisp are not allowed to be redefined.
  - Zambyte 3y ago
    It may be semantically invalid in Common Lisp, but it is syntactically valid in Lisp (as seen by observing different dialects).
    - lispm 3y ago
      The term "Lisp" is undefined. Common Lisp is an actual standard for a programming language with a specification. Its core symbols are reserved identifiers. Anyway, if you would be allowed to reimplement a built-in operator, then from then on you would be using the new operator and you would be limited to its syntax. Common Lisp OTOH provides namespaces (called "package") and there is a pre-defined namespace "COMMON-LISP" for the core language.
      - Zambyte 3y ago
        > The term "Lisp" is undefined This hasn't been a problem in this thread thus far, but to be explicit, this seems like a good definition: https://en.wikipedia.org/wiki/Lisp_%28programming_language%29 https://en.wikipedia.org/wiki/Lisp_%28programming_language%2... Given that definition, we can see that there are many actual standards for programming languages with specifications under the name "Lisp". Scheme - as was mentioned in this thread, is one such standard, along with Common Lisp. > Anyway, if you would be allowed to reimplement a built-in operator, then from then on you would be using the new operator and you would be limited to its syntax. I think you're arguing the merits of doing something like redefining define here, which is not the subject of this comment chain. Of course such behavior is questionable at best. The comment chain is discussing if such a thing would be valid in Lisp - and, in some dialects (such as Scheme) it is. Scheme also has a feature called "libraries" which makes such behavior more feasible, as you could still have access to the shadowed primitive. Consider: gosh[r7rs.user]$ (import (prefix (scheme base) base:)) gosh[r7rs.user]$ (define (define x) 5) define gosh[r7rs.user]$ (base:define x (+ (define define) (define define))) x gosh[r7rs.user]$ x 10
        lispm 3y ago
        > Scheme - as was mentioned in this thread, is one such standard, along with Common Lisp. Then see the Scheme standards. They include a syntax definition. > The comment chain is discussing if such a thing would be valid in Lisp - and, in some dialects (such as Scheme) it is. Lisp is not a defined language, thus you can assume anything. My point is: Lisp dialects have syntax. This syntax is usually defined on top of s-expressions. S-expressions also have a syntax, but this syntax usually (there are exceptions) describes only data types (lists, conses, numbers, strings, symbols, arrays, records/structures, bit vectors, pathnames, ...) and not the actual programming language with its operators (functions, macros, special operators) & their way to define and invoke them. Example: The LET operator in various Lisp dialects there have a specific syntax. This syntax is not the syntax of simple function calls like (operator arg0 ... args). R7RS small defines this syntax (and also calls it syntax): (let ⟨bindings⟩ ⟨body⟩) (let ⟨variable⟩ (⟨binding spec⟩*) ⟨tail body⟩) ⟨Bindings⟩ has the form ((⟨variable1⟩ ⟨init1⟩) ...) If you write let forms which don't use this syntax, then they are not valid R7RS Scheme let forms, even though they are valid s-expressions.

lispm 3y ago

Check the Common Lisp specification some time. Every language construct has a syntax definition: function calls, macro calls, lambda expressions, special operator calls, ..., every macro.