How do I call the `function` function?












16















I am trying to call the function `function` to define a function in R code.



As we all know™️, `function`is a .Primitive that’s used internally by R to define functions when the user uses the conventional syntax, i.e.



mean1 = function (x, ...) base::mean(x, ...)


But there’s nothing preventing me from calling that primitive directly. Or so I thought. I can call other primitives directly (and even redefine them; for instance, in a moment of madness I overrode R’s builtin `for`). So this is in principle possible.



Yet I cannot get it to work for `function`. Here’s what I tried:



# Works

mean2 = as.function(c(formals(mean), quote(mean(x, ...))))



# Works

mean3 = eval(call('function', formals(mean), quote(mean(x, ...))))



# Error: invalid formal argument list for "function"

mean4 = `function`(formals(mean), quote(mean(x, ...)))


The fact that mean3 in particular works indicates to me that mean4 should work. But it doesn’t. Why?



I checked the definition of the `function` primitive in the R source. do_function is defined in eval.c. And I see that it calls CheckFormals, which ensures that each argument is a symbol, and this fails. But why does it check this, and what does that mean?



And most importantly: Is there a way of calling the `function` primitive directly?




Just to clarify: There are trivial workarounds (this question lists two, and there’s at least a third). But I’d like to understand how this (does not) works.






r







share|improve this question























  • Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

    – Konrad Rudolph
    3 hours ago











  • Related: stackoverflow.com/questions/12982528/…

    – Artem Sokolov
    3 hours ago











  • @Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

    – Artem Sokolov
    3 hours ago











  • @ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

    – Konrad Rudolph
    3 hours ago


















16















I am trying to call the function `function` to define a function in R code.



As we all know™️, `function`is a .Primitive that’s used internally by R to define functions when the user uses the conventional syntax, i.e.



mean1 = function (x, ...) base::mean(x, ...)


But there’s nothing preventing me from calling that primitive directly. Or so I thought. I can call other primitives directly (and even redefine them; for instance, in a moment of madness I overrode R’s builtin `for`). So this is in principle possible.



Yet I cannot get it to work for `function`. Here’s what I tried:



# Works

mean2 = as.function(c(formals(mean), quote(mean(x, ...))))



# Works

mean3 = eval(call('function', formals(mean), quote(mean(x, ...))))



# Error: invalid formal argument list for "function"

mean4 = `function`(formals(mean), quote(mean(x, ...)))


The fact that mean3 in particular works indicates to me that mean4 should work. But it doesn’t. Why?



I checked the definition of the `function` primitive in the R source. do_function is defined in eval.c. And I see that it calls CheckFormals, which ensures that each argument is a symbol, and this fails. But why does it check this, and what does that mean?



And most importantly: Is there a way of calling the `function` primitive directly?




Just to clarify: There are trivial workarounds (this question lists two, and there’s at least a third). But I’d like to understand how this (does not) works.






r







share|improve this question























  • Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

    – Konrad Rudolph
    3 hours ago











  • Related: stackoverflow.com/questions/12982528/…

    – Artem Sokolov
    3 hours ago











  • @Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

    – Artem Sokolov
    3 hours ago











  • @ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

    – Konrad Rudolph
    3 hours ago
















16












16








16


4






I am trying to call the function `function` to define a function in R code.



As we all know™️, `function`is a .Primitive that’s used internally by R to define functions when the user uses the conventional syntax, i.e.



mean1 = function (x, ...) base::mean(x, ...)


But there’s nothing preventing me from calling that primitive directly. Or so I thought. I can call other primitives directly (and even redefine them; for instance, in a moment of madness I overrode R’s builtin `for`). So this is in principle possible.



Yet I cannot get it to work for `function`. Here’s what I tried:



# Works

mean2 = as.function(c(formals(mean), quote(mean(x, ...))))



# Works

mean3 = eval(call('function', formals(mean), quote(mean(x, ...))))



# Error: invalid formal argument list for "function"

mean4 = `function`(formals(mean), quote(mean(x, ...)))


The fact that mean3 in particular works indicates to me that mean4 should work. But it doesn’t. Why?



I checked the definition of the `function` primitive in the R source. do_function is defined in eval.c. And I see that it calls CheckFormals, which ensures that each argument is a symbol, and this fails. But why does it check this, and what does that mean?



And most importantly: Is there a way of calling the `function` primitive directly?




Just to clarify: There are trivial workarounds (this question lists two, and there’s at least a third). But I’d like to understand how this (does not) works.






r







share|improve this question














I am trying to call the function `function` to define a function in R code.



As we all know™️, `function`is a .Primitive that’s used internally by R to define functions when the user uses the conventional syntax, i.e.



mean1 = function (x, ...) base::mean(x, ...)


But there’s nothing preventing me from calling that primitive directly. Or so I thought. I can call other primitives directly (and even redefine them; for instance, in a moment of madness I overrode R’s builtin `for`). So this is in principle possible.



Yet I cannot get it to work for `function`. Here’s what I tried:



# Works

mean2 = as.function(c(formals(mean), quote(mean(x, ...))))



# Works

mean3 = eval(call('function', formals(mean), quote(mean(x, ...))))



# Error: invalid formal argument list for "function"

mean4 = `function`(formals(mean), quote(mean(x, ...)))


The fact that mean3 in particular works indicates to me that mean4 should work. But it doesn’t. Why?



I checked the definition of the `function` primitive in the R source. do_function is defined in eval.c. And I see that it calls CheckFormals, which ensures that each argument is a symbol, and this fails. But why does it check this, and what does that mean?



And most importantly: Is there a way of calling the `function` primitive directly?




Just to clarify: There are trivial workarounds (this question lists two, and there’s at least a third). But I’d like to understand how this (does not) works.






r




r






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 5 hours ago









Konrad RudolphKonrad Rudolph

397k1017861033




397k1017861033













  • Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

    – Konrad Rudolph
    3 hours ago











  • Related: stackoverflow.com/questions/12982528/…

    – Artem Sokolov
    3 hours ago











  • @Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

    – Artem Sokolov
    3 hours ago











  • @ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

    – Konrad Rudolph
    3 hours ago





















  • Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

    – Konrad Rudolph
    3 hours ago











  • Related: stackoverflow.com/questions/12982528/…

    – Artem Sokolov
    3 hours ago











  • @Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

    – Artem Sokolov
    3 hours ago











  • @ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

    – Konrad Rudolph
    3 hours ago



















Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

– Konrad Rudolph
3 hours ago





Duplicate of stackoverflow.com/q/53218422/1968 (I swear I found this afterwards)

– Konrad Rudolph
3 hours ago













Related: stackoverflow.com/questions/12982528/…

– Artem Sokolov
3 hours ago





Related: stackoverflow.com/questions/12982528/…

– Artem Sokolov
3 hours ago













@Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

– Artem Sokolov
3 hours ago





@Moody's answer in the link above points out rlang::new_function, which can be called directly as a function and does essentially what function does.

– Artem Sokolov
3 hours ago













@ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

– Konrad Rudolph
3 hours ago







@ArtemSokolov … sure but that does exactly what my mean3 definition does. I’m well aware of workarounds, I was just curious why it doesn’t seem to work.

– Konrad Rudolph
3 hours ago














2 Answers
2






active

oldest

votes


















7














This is because function is a special primitive:



typeof(`function`)

#> [1] "special"


The arguments are not evaluated, so you have actually passed quote(formals(mean)) instead of the value of formals(mean). I don't think there's a way of calling function directly without evaluation tricks, except with an empty formals list which is just NULL.






share|improve this answer



















  • 1





    I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

    – Konrad Rudolph
    3 hours ago








  • 1





    Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

    – lionel
    3 hours ago











  • Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

    – Konrad Rudolph
    3 hours ago





















4














For completeness’ sake, lionel’s answer hints at a way of calling `function` after all. Unfortunately it’s rather restricted, since we cannot pass any argument definition except for NULL:



mean5 = `function`(NULL, mean(x, ...))

formals(mean5) = formals(mean)


(Note the lack of quoting around the body!)



This is of course utterly unpractical (and formals<- internally calls as.function anyway.)






share|improve this answer























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    2 Answers
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    2 Answers
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    active

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    7














    This is because function is a special primitive:



    typeof(`function`)
    
#> [1] "special"


    The arguments are not evaluated, so you have actually passed quote(formals(mean)) instead of the value of formals(mean). I don't think there's a way of calling function directly without evaluation tricks, except with an empty formals list which is just NULL.






    share|improve this answer



















    • 1





      I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

      – Konrad Rudolph
      3 hours ago








    • 1





      Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

      – lionel
      3 hours ago











    • Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

      – Konrad Rudolph
      3 hours ago


















    7














    This is because function is a special primitive:



    typeof(`function`)
    
#> [1] "special"


    The arguments are not evaluated, so you have actually passed quote(formals(mean)) instead of the value of formals(mean). I don't think there's a way of calling function directly without evaluation tricks, except with an empty formals list which is just NULL.






    share|improve this answer



















    • 1





      I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

      – Konrad Rudolph
      3 hours ago








    • 1





      Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

      – lionel
      3 hours ago











    • Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

      – Konrad Rudolph
      3 hours ago
















    7












    7








    7







    This is because function is a special primitive:



    typeof(`function`)
    
#> [1] "special"


    The arguments are not evaluated, so you have actually passed quote(formals(mean)) instead of the value of formals(mean). I don't think there's a way of calling function directly without evaluation tricks, except with an empty formals list which is just NULL.






    share|improve this answer













    This is because function is a special primitive:



    typeof(`function`)
    
#> [1] "special"


    The arguments are not evaluated, so you have actually passed quote(formals(mean)) instead of the value of formals(mean). I don't think there's a way of calling function directly without evaluation tricks, except with an empty formals list which is just NULL.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 3 hours ago









    lionellionel

    2,9221518




    2,9221518








    • 1





      I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

      – Konrad Rudolph
      3 hours ago








    • 1





      Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

      – lionel
      3 hours ago











    • Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

      – Konrad Rudolph
      3 hours ago
















    • 1





      I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

      – Konrad Rudolph
      3 hours ago








    • 1





      Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

      – lionel
      3 hours ago











    • Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

      – Konrad Rudolph
      3 hours ago










    1




    1





    I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

    – Konrad Rudolph
    3 hours ago







    I actually tried quoting the formals (as well as using alist), yet as you noticed this also doesn’t work. typeof(`for`) is also “special”, but calling ` for ` manually works.

    – Konrad Rudolph
    3 hours ago






    1




    1





    Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

    – lionel
    3 hours ago





    Yeah because for takes a symbol and two expressions, for which there is parser syntax. There is no explicit parser syntax for creating a pairlist literal, which is what function() takes.

    – lionel
    3 hours ago













    Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

    – Konrad Rudolph
    3 hours ago







    Indeed. I just figured out that you can call it with a manually generated pairlist — but once again only indirectly because, as you said, there’s no pairlist literal syntax.

    – Konrad Rudolph
    3 hours ago















    4














    For completeness’ sake, lionel’s answer hints at a way of calling `function` after all. Unfortunately it’s rather restricted, since we cannot pass any argument definition except for NULL:



    mean5 = `function`(NULL, mean(x, ...))
    
formals(mean5) = formals(mean)


    (Note the lack of quoting around the body!)



    This is of course utterly unpractical (and formals<- internally calls as.function anyway.)






    share|improve this answer




























      4














      For completeness’ sake, lionel’s answer hints at a way of calling `function` after all. Unfortunately it’s rather restricted, since we cannot pass any argument definition except for NULL:



      mean5 = `function`(NULL, mean(x, ...))
      
formals(mean5) = formals(mean)


      (Note the lack of quoting around the body!)



      This is of course utterly unpractical (and formals<- internally calls as.function anyway.)






      share|improve this answer


























        4












        4








        4







        For completeness’ sake, lionel’s answer hints at a way of calling `function` after all. Unfortunately it’s rather restricted, since we cannot pass any argument definition except for NULL:



        mean5 = `function`(NULL, mean(x, ...))
        
formals(mean5) = formals(mean)


        (Note the lack of quoting around the body!)



        This is of course utterly unpractical (and formals<- internally calls as.function anyway.)






        share|improve this answer













        For completeness’ sake, lionel’s answer hints at a way of calling `function` after all. Unfortunately it’s rather restricted, since we cannot pass any argument definition except for NULL:



        mean5 = `function`(NULL, mean(x, ...))
        
formals(mean5) = formals(mean)


        (Note the lack of quoting around the body!)



        This is of course utterly unpractical (and formals<- internally calls as.function anyway.)







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 3 hours ago









        Konrad RudolphKonrad Rudolph

        397k1017861033




        397k1017861033






























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