evalSource: Use Function Definitions from a Source File without...

evalSourceR Documentation

Use Function Definitions from a Source File without Reinstalling a Package


Definitions of functions and/or methods from a source file are inserted into a package, using the trace mechanism. Typically, this allows testing or debugging modified versions of a few functions without reinstalling a large package.


evalSource(source, package = "", lock = TRUE, cache = FALSE)

insertSource(source, package = "", functions = , methods = ,
           force = )



A file to be parsed and evaluated by evalSource to find the new function and method definitions.

The argument to insertSource can be an object of class "sourceEnvironment" returned from a previous call to evalSource If a file name is passed to insertSource it calls evalSource to obtain the corresponding object. See the section on the class for details.


Optionally, the name of the package to which the new code corresponds and into which it will be inserted. Although the computations will attempt to infer the package if it is omitted, the safe approach is to supply it. In the case of a package that is not attached to the search list, the package name must be supplied.

functions, methods

Optionally, the character-string names of the functions to be used in the insertion. Names supplied in the functions argument are expected to be defined as functions in the source. For names supplied in the methods argument, a table of methods is expected (as generated by calls to setMethod, see the details section); methods from this table will be inserted by insertSource. In both cases, the revised function or method is inserted only if it differs from the version in the corresponding package as loaded.

If what is omitted, the results of evaluating the source file will be compared to the contents of the package (see the details section).

lock, cache

Optional arguments to control the actions taken by evalSource. If lock is TRUE, the environment in the object returned will be locked, and so will all its bindings. If cache is FALSE, the normal caching of method and class definitions will be suppressed during evaluation of the source file.

The default settings are generally recommended, the lock to support the credibility of the object returned as a snapshot of the source file, and the second so that method definitions can be inserted later by insertSource using the trace mechanism.


If FALSE, only functions currently in the environment will be redefined, using trace. If TRUE, other objects/functions will be simply assigned. By default, TRUE if neither the functions nor the methods argument is supplied.


The source file is parsed and evaluated, suppressing by default the actual caching of method and class definitions contained in it, so that functions and methods can be tested out in a reversible way. The result, if all goes well, is an environment containing the assigned objects and metadata corresponding to method and class definitions in the source file.

From this environment, the objects are inserted into the package, into its namespace if it has one, for use during the current session or until reverting to the original version by a call to untrace. The insertion is done by calls to the internal version of trace, to make reversion possible.

Because the trace mechanism is used, only function-type objects will be inserted, functions themselves or S4 methods.

When the functions and methods arguments are both omitted, insertSource selects all suitable objects from the result of evaluating the source file.

In all cases, only objects in the source file that differ from the corresponding objects in the package are inserted. The definition of “differ” is that either the argument list (including default expressions) or the body of the function is not identical. Note that in the case of a method, there need be no specific method for the corresponding signature in the package: the comparison is made to the method that would be selected for that signature.

Nothing in the computation requires that the source file supplied be the same file as in the original package source, although that case is both likely and sensible if one is revising the package. Nothing in the computations compares source files: the objects generated by evaluating source are compared as objects to the content of the package.


An object from class "sourceEnvironment", a subclass of "environment" (see the section on the class) The environment contains the versions of all object resulting from evaluation of the source file. The class also has slots for the time of creation, the source file and the package name. Future extensions may use these objects for versioning or other code tools.

The object returned can be used in debugging (see the section on that topic) or as the source argument in a future call to insertSource. If only some of the revised functions were inserted in the first call, others can be inserted in a later call without re-evaluating the source file, by supplying the environment and optionally suitable functions and/or methods argument.


Once a function or method has been inserted into a package by insertSource, it can be studied by the standard debugging tools; for example, debug or the various versions of trace.

Calls to trace should take the extra argument edit = env, where env is the value returned by the call to evalSource. The trace mechanism has been used to install the revised version from the source file, and supplying the argument ensures that it is this version, not the original, that will be traced. See the example below.

To turn tracing off, but retain the source version, use trace(x, edit = env) as in the example. To return to the original version from the package, use untrace(x).

Class "sourceEnvironment"

Objects from this class can be treated as environments, to extract the version of functions and methods generated by evalSource. The objects also have the following slots:


The character-string name of the package to which the source code corresponds.


The date and time that the source file was evaluated (usually from a call to Sys.time).


The character-string name of the source file used.

Note that using the environment does not change the dateCreated.

See Also

trace for the underlying mechanism, and also for the edit= argument that can be used for somewhat similar purposes; that function and also debug and setBreakpoint, for techniques more oriented to traditional debugging styles. The present function is directly intended for the case that one is modifying some of the source for an existing package, although it can be used as well by inserting debugging code in the source (more useful if the debugging involved is non-trivial). As noted in the details section, the source file need not be the same one in the original package source.


## Not run: 
## Suppose package P0 has a source file "all.R"
## First, evaluate the source, and from it
## insert the revised version of methods for summary()
  env <- insertSource("./P0/R/all.R", package = "P0",
     methods = "summary")
## now test one of the methods, tracing  the version from the source
  trace("summary", signature = "myMat", browser, edit = env)
## After testing, remove the browser() call but keep the source
  trace("summary", signature = "myMat", edit = env)
## Now insert all the (other) revised functions and methods
## without re-evaluating the source file.
## The package name is included in the object env.

## End(Not run)