Re: [R] forcing evaluation of a char string argument

[Charles C. Berry]

On Wed, 22 Dec 2010, rballen wrote:


Why does x in "assign(x)" correctly evaluate to "rank" where
UseMethod(func) does not get correctly evaluated?

Because it is the body of a function definition.

If you want to plug in the value of 'func' in the body of that function, 
you need to do something like this:

toGeneric <- 
function(func) {
        env<-environment(get(func))

        # default method of new generic = the original function
        assign(paste(func,".default",sep=""),get(func),pos=env)
        foo <- function(x,...) {}
        lf <- list(x=func)
        body.foo <- substitute(UseMethod(x),lf)
        body(foo)<-body.foo
        assign(func,foo,pos=env)
}

BTW, are you sure you know what 'env' evaluates to?? (It is NOT the 
environment of the object named by the value of func in the parent.frame 
of toGeneric.)

HTH,

Chuck

Can we use as.call(list(UseMethod,func))?

assign(paste(func,".default",sep=""),get(func),pos=env)

assign(func,function(x,...) UseMethod(func),pos=env)

On Wed, Dec 22, 2010 at 9:03 PM, William Dunlap [via R]
<ml-node+3161542-1898476570-206...@n4.nabble.com> wrote:
Try the following, which I haven't tested much
and needs more error checking (e.g., to see that
the function is not already generic and that
its argument list is compatible with (x,...)).
I put in the print statements to show what
the calls to substitute() do.

toGeneric <- function (funcName) {
?? ?? stopifnot(is.character(funcName))
?? ?? funcItself <- get(funcName)
?? ?? stopifnot(is.function(funcItself))
?? ?? envir <- environment(funcItself)
?? ?? tmp <- substitute(funcSymbol <- function(x, ...)
UseMethod(funcName),
?? ?? ?? ?? list(funcSymbol = as.symbol(funcName), funcName = funcName))
?? ?? print(tmp)
?? ?? eval(tmp, envir = envir)
?? ?? tmp <- substitute(defaultSymbol <- funcItself, list(defaultSymbol =
as.symbol(paste(sep = ".",
?? ?? ?? ?? funcName, "default")), funcItself = funcItself))
?? ?? print(tmp)
?? ?? eval(tmp, envir = envir)
}

E.g.,

?? ??> wsx <- function(x, base=2)log(x, base=base)
?? ??> toGeneric("wsx")
?? ??wsx <- function(x, ...) UseMethod("wsx")
?? ??wsx.default <- function (x, base = 2)
?? ??log(x, base = base)
?? ??> wsx
?? ??function (x, ...)
?? ??UseMethod("wsx")
?? ??> wsx.default
?? ??function (x, base = 2)
?? ??log(x, base = base)

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of rballen
Sent: Wednesday, December 22, 2010 2:42 PM
To: [hidden email]
Subject: [R] forcing evaluation of a char string argument


I'm trying to make a function to turn a regular function into
an S3 generic
one. I want myMethod to be:

function(x,...) UseMethod("myMethod")

But I keep getting:

function(x,...) UseMethod(func)

Here's the function:

toGeneric<-function(func) {
env<-environment(get(func))

# default method of new generic = the original function
assign(paste(func,".default",sep=""),get(func),pos=env)

assign(func,function(x,...) UseMethod(func),pos=env)
}

toGeneric("myMethod")

I messed around with force, substitute, and deparse, but I
can't get any of
those to help.

Thanks.
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Charles C. Berry                            Dept of Family/Preventive Medicine
cbe...@tajo.ucsd.edu                        UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901

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