match.fun
Function Verification for "Function Variables"
Description
Attempts to find the function specified by the FUN argument.
Usage
match.fun(FUN, descend = TRUE)
Arguments
| FUN |
a function, a function name, or a character string.
|
| descend |
a logical value. If TRUE (the default), the search continues past matching variables that are not functions.
If FALSE, only the first matching variable is considered.
|
Details
Calling match.fun with descend=TRUE is like calling get with mode='function'.
However, first it inspects the FUN argument to determine the function name. If FUN
is a function, it just returns. If FUN is a character vector with the length one, or if FUN is a symbol, it uses
get to find the function in the environment of the parent of the caller. Otherwise, it attempts to evaluate FUN
as a symbol (using substitute twice). If the evaluation fails, it generates an error.
See the examples below for some tricky cases it handles.
Value
returns a function, as specified by the FUN argument.
If no function could be found, it generates an error.
See Also
Examples
f <- function(FUN, ...) { FUN <- match.fun(FUN); FUN(...) }
sum <- 42 # Variable hiding the real function
f('sum', 1,2,3)
f(sum, 1,2,3)
match.fun("ls")
match.fun(ls)
match.fun(c("ls","sum"))
# 'c("ls", "sum")' is not a function, character or symbol