Create or test for objects of
mode (or type:
1 2 3
a non-empty character string naming the function to be called.
arguments to be part of the call.
an arbitrary R object.
call returns an unevaluated function call, that is, an
unevaluated expression which consists of the named function applied to
the given arguments (
name must be a quoted string which gives
the name of a function to be called). Note that although the call is
unevaluated, the arguments
... are evaluated.
call is a primitive, so the first argument is
name and the remaining arguments as arguments for the
constructed call: if the first argument is named the name must
is.call is used to determine whether
x is a call (i.e.,
"call"). Note that
is.language is also
TRUE for calls (but also for
is.call() is false).
Objects of mode
"list" can be coerced to mode
The first element of the list becomes the function part of the call,
so should be a function or the name of one (as a symbol; a quoted
string will not do).
All three are primitive functions.
call should not be used to attempt to evade restrictions on the
.Internal and other non-API calls.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.
do.call for calling a function by name and argument
Recall for recursive calling of functions;
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
is.call(call) #-> FALSE: Functions are NOT calls ## set up a function call to round with argument 10.5 cl <- call("round", 10.5) is.call(cl) # TRUE cl identical(quote(round(10.5)), # <- less functional, but the same cl) # TRUE ## such a call can also be evaluated. eval(cl) #  10 class(cl) # "call" typeof(cl)# "language" is.call(cl) && is.language(cl) # always TRUE for "call"s A <- 10.5 call("round", A) # round(10.5) call("round", quote(A)) # round(A) f <- "round" call(f, quote(A)) # round(A) ## if we want to supply a function we need to use as.call or similar f <- round ## Not run: call(f, quote(A)) # error: first arg must be character (g <- as.call(list(f, quote(A)))) eval(g) ## alternatively but less transparently g <- list(f, quote(A)) mode(g) <- "call" g eval(g) ## see also the examples in the help for do.call
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