Function Calls

Description

Create or test for objects ofmode"call" (or"(", see Details).

Usage

call(name, ...)is.call(x)as.call(x)

Arguments

Details

call

returns an unevaluated function call, that is, anunevaluated expression which consists of the named function applied tothe given arguments (name must be a string which givesthe name of a function to be called). Note that although the call isunevaluated, the arguments... are evaluated.

call is a primitive, so the first argument istaken asname and the remaining arguments as arguments for theconstructed call: if the first argument is named the name mustpartially matchname.

is.call

is used to determine whetherx is a call (i.e.,of mode"call" or"("). Note that

• is.call(x) is strictly equivalent totypeof(x) == "language".

• is.language() is also true for calls (but alsoforsymbols andexpressions whereis.call() is false).

as.call(x):

Objects of mode"list" can be coerced to mode"call".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 character string will not do).

If you think of usingas.call(<string>), consider usingstr2lang(*) which is an efficient version ofparse(text=*).Note thatcall() andas.call(), whenapplicable, are much preferable to theseparse() basedapproaches.

All three are primitive functions.

as.call is generic: you can write methods to handle specificclasses of objects, see InternalMethods.

Warning

call should not be used to attempt to evade restrictions on theuse of.Internal and other non-API calls.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)The New S Language.Wadsworth & Brooks/Cole.

See Also

do.call for calling a function by name and argumentlist;Recall for recursive calling of functions;furtheris.language,expression,function.

Producingcalls etc from character:str2lang andparse.

Examples

is.call(call) #-> FALSE: Functions are NOT calls## set up a function call to round with argument 10.5cl <- call("round", 10.5)is.call(cl) # TRUEclidentical(quote(round(10.5)), # <- less functional, but the same          cl) # TRUE## such a call can also be evaluated.eval(cl) # [1] 10class(cl) # "call"typeof(cl)# "language"is.call(cl) && is.language(cl) # always TRUE for "call"sA <- 10.5call("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 similarf <- 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 transparentlyg <- list(f, quote(A))mode(g) <- "call"geval(g)## see also the examples in the help for do.call