languageEl
Extract or replace parts of expressions

### Description

Extracts or replaces parts of expressions

### Usage

    languageEl(object, which)
    languageEl(object, which) <- value

### Arguments

object | a function or a call object.
which | either a character string or a number specifying which element of the object to extract or replace.
value | any object that is valid as part of a function or call object. Typically a constant or a call object.

### Details

For calls to certain functions with special syntactical meaning (if, for, while, and {), the name of the function is not counted when which is a numeric value.
Value
When extracting, returns essentially the same result as as.list(object)[[which]].
When replacing, the which'th element of the object is replaced by value, and the return value is value.
Examples

    languageEl(quote(f(x, y=log(5))), "y")
    languageEl(quote(f(x, y=log(5))), 3)
    f <- function(x, y=log(x)) y
    languageEl(f, "y") <- quote(1/x)
    f

Package methods version 6.1.5-18
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