typetracer is an R package to trace function parameter
types. The R language includes a
set of defined types, but the language itself is “absurdly
dynamic”[1], and lacks any way to specify which types are expected
by any expression. The typetracer package enables code to
be traced to extract detailed information on the properties of
parameters passed to R functions. typetracer can trace
individual functions or entire packages, as demonstrated below.
The package can be installed with the following command:
remotes::install_github ("mpadge/typetracer")Then loaded for use by calling library:
library (typetracer)typetracer works by “injecting” tracing code into the
body of a function using the
inject_tracer() function. Locally-defined functions can
be traced by simply passing the functions directly to
inject_tracer(). The following example includes four
parameters, including ... to allow passing of additional
and entirely arbitrary parameter types and values.
f <- function (x, y, z, ...) {
x * x + y * y
}
inject_tracer (f)After injecting the typetracer code, calls to the
function, f, will “trace” each parameter of the function,
by capturing both unevaluated and evaluated representations at the point
at which the function is first called. These values can be accessed with
the
load_traces function, which returns a
data.frame object (in tibble format) with
one row for each parameter from each function call.
val <- f (
x = 1:2,
y = 3:4 + 0.,
a = "blah",
b = list (a = 1, b = "b"),
f = a ~ b
)
x <- load_traces ()
x
## # A tibble: 7 × 12
## trace_number fn_name fn_call_hash par_name class typeof mode storage_mode
## <int> <chr> <chr> <chr> <I<list>> <chr> <chr> <chr>
## 1 0 f acDVZHbn x <chr [1]> integ… nume… integer
## 2 0 f acDVZHbn y <chr [1]> double nume… double
## 3 0 f acDVZHbn z <chr [1]> NULL NULL NULL
## 4 0 f acDVZHbn ... <chr [1]> NULL NULL NULL
## 5 0 f acDVZHbn a <chr [1]> chara… char… character
## 6 0 f acDVZHbn b <chr [1]> list list list
## 7 0 f acDVZHbn f <chr [1]> langu… call language
## # … with 4 more variables: length <int>, formal <named list>, uneval <I<list>>,
## # eval <I<list>>Each row of the result returned by load_traces()
represents one parameter passed to one function call. Each function call
itself represents a single “trace” as enumerated by the
trace_number column, and also uniquely identified by an
arbitrary function call hash (fn_call_hash). The remaining
columns of the trace data define the properties of each parameter,
p, as:
par_name: Name of parameter.class: List of classes of parameter.typeof: Result of typeof(p).mode: Result of mode(p).storage_mode: Result of
storage.mode(p).length: Result of length(p).formal: Result of formals(f)[["p"]], as
named list item with default value where specified.uneval: Parameters as passed to the function call prior
to evaluation within function environment.eval: Evaluated version of parameter.The results above show that all parameters of the function,
f(), were successfully traced, including the additional
parameters, a, b, and f, passed
as part of the ... argument. Such additional parameters can
be identified through having a "formal" entry of
NULL, indicating that they are not part of the formal
arguments to the function.
That result can also be used to demonstrate the difference between the unevaluated and evaluated forms of parameters:
x$uneval [x$par_name %in% c ("b", "f")]
## $b
## [1] "list(a = 1, b = \"b\")"
##
## $f
## [1] "a ~ b"
x$eval [x$par_name %in% c ("b", "f")]
## $b
## $b$a
## [1] 1
##
## $b$b
## [1] "b"
##
##
## $f
## a ~ b
## <environment: 0x561e5dd16c38>Unevaluated parameters are generally converted to equivalent character expressions.
The typeof, mode, and
storage_mode columns are similar, yet may hold distinct
information for certain types of parameters. The conditions under which
these values differ are complex, and depend among other things on the
version of R itself. typeof alone should generally provide
sufficient information, although this list of differences
may provide further insight into whether the other columns may provide
useful additional information.
Traces themselves are saved in the temporary directory of the current
R session, and the
load_traces() function simply loads all traces created
in that session. The
function clear_traces() removes all traces, so that load_traces()
will only load new traces produced after that time.
It is important after applying the
inject_tracer() function to restore the functions back
to their original form through calling the
obverse uninject_tracer() function. For the function,
r, above, this simply requires,
uninject_tracer (f)
## [1] TRUEBecause typetracer modifies the internal code of
functions as defined within a current R session, we strongly recommend
restarting your R session after using typetracer, to ensure
expected function behaviour is restored.
This section presents a more complex example tracing all function
calls from the
rematch package, chosen because it has less code than
almost any other package on CRAN. The following single line traces
function calls in all examples for the nominated package. The
trace_package() function automatically injects tracing
code into every function within the package, so there is no need to
explicitly call the
inject_tracer() function.
res <- trace_package ("rematch")
res
## # A tibble: 8 × 13
## trace_number fn_name fn_call_hash par_name class typeof mode storage_mode
## <int> <chr> <chr> <chr> <I<list> <chr> <chr> <chr>
## 1 0 re_match DMxsBqEc pattern <chr> chara… char… character
## 2 0 re_match DMxsBqEc text <chr> chara… char… character
## 3 0 re_match DMxsBqEc perl <chr> logic… logi… logical
## 4 0 re_match DMxsBqEc ... <chr> NULL NULL NULL
## 5 1 re_match clziFvXN pattern <chr> chara… char… character
## 6 1 re_match clziFvXN text <chr> chara… char… character
## 7 1 re_match clziFvXN perl <chr> logic… logi… logical
## 8 1 re_match clziFvXN ... <chr> NULL NULL NULL
## # … with 5 more variables: length <int>, formal <named list>, uneval <I<list>>,
## # eval <I<list>>, source <chr>The data.frame returned by the
trace_package() function includes one more column than the
result directly returned by load_traces(). This column is
called “source”, and identifies the source-code object which generated
each trace:
unique (res$source)
## [1] "rd_re_match"Tracing an installed package generally only extracts traces from
example code, as documented in help, or .Rd, files. These
are identified by the “rd_” prefix on the source call, with the
rematch package including only one .Rd
file.
The
trace_package() function also includes an additional
parameter, types, which defaults to
c ("examples", "tests"), so that traces are also by default
generated for all tests included with local source packages (or for
packages installed to include test files). The “source” column for test
files identifies the names of each test, prefixed with “test_”. Other
than this column, the results are the same as shown above for
load_traces(), with one line for every parameter passed to
every function call in the examples.
The
trace_package() function also accepts an argument,
functions, specifying which functions from a package should
be traced. For example,
x <- trace_package ("stats", functions = "sd")
## # A tibble: 2 × 13
## trace_number fn_name fn_call_hash par_name class typeof mode storage_mode
## <int> <chr> <chr> <chr> <I<list>> <chr> <chr> <chr>
## 1 0 sd EzasZOKV x <chr [1]> integ… nume… integer
## 2 0 sd EzasZOKV na.rm <chr [1]> logic… logi… logical
## # … with 5 more variables: length <int>, formal <I<list>>, uneval <I<list>>,
## # eval <I<list>>, source <chr>This package extends on concepts previously developed in other R packages, notably including:
typed
package by @moodymudskippercontractr
package by @aviralg & @fikovnikPlus work explained in detail in this footnote:
[1] Alexi Turcotte & Jan Vitek (2019), Towards a Type System for R, ICOOOLPS ’19: Proceedings of the 14th Workshop on Implementation, Compilation, Optimization of Object-Oriented Languages, Programs and Systems. Article No. 4, Pages 1–5, https://doi.org/10.1145/3340670.3342426