explorations/extractFuns/whyExtractedDifferent.md

In duncantl/CodeAnalysis: Tools for Static Analysis of R code

Why is the size of a function different from (size of extracted functions + size of reduced function after extraction)?

One reason is that we are remove fun = function()... calls so we are removing the = and left and right hand side. When we compute the size of the extracted functions, we won't see the fun and =. So we have lost 2 elements for every extracted functions.

But that wasn't enough.

It turns out that

1. when there are multiple levels of nested named functions within the top-level function we don't recursively extract them (yet?!) and so if we have the situation below, we get g and h as the extracted functions, but g will continue to contain h. Accordingly, the number of terms in g and h double counts those in h. This is why are calculations for back and then diff were always negative, i.e., more in the reduced + sum(extracted) + 2*legnth(extracted).

f = function() {
     g = function() {
        h = function() {

        }
        ...
     }
     ...
}

1. There were bugs in the mkModifyCodeWalker() which we fixed given this long debugging investigation.
   • See toolsExtract.R

Moved from tools_package.md and written before we solved the issue and noted it above.

The size of the original function is not necessarily the same size as the number of terms in the modified function and the sum of the number of terms in the

cbind(d$numTerms - d$sizeNestedFunctions, d$afterExtractedNumTerms)

     [,1] [,2]
[1,]  200   56
[2,] 3193 3072
[3,] 1256 1206
[4,]  441  376
[5,] 1757 1702
[6,]  441  390

This is in part due to the var <- function() {...} being removed and the var and <- are not count. So for every named nested functions (the one we take out), we remove three terms and only count

cbind(d$numTerms - d$sizeNestedFunctions - 2*d$numFunctions, d$afterExtractedNumTerms)

v = "makeJSS" library(codetools)

The nested functions

ctr = CodeAnalysis:::mkCounter () invisible(lapply(nfns[[v]], walkCode, ctr))

the original version

ctr2 = CodeAnalysis:::mkCounter() invisible(walkCode(tfns[[v]], ctr2)) length(ctr2$.els())

the reduced/extracted version

ctr3 = CodeAnalysis:::mkCounter() invisible(walkCode(ex[[v]]$newFun, ctr3)) length(ctr3$.els())

getTerms = function(code) { ctr = CodeAnalysis:::mkCounter(); walkCode(code, ctr); ctr$.els()}

getTerms(quote(function() a))

[[1]]
`function`

[[2]]
NULL

[[3]]
a

[[4]]
function() a

getTerms(function() a)

[[1]]
NULL

[[2]]
a

f = function(x, y) { a = 1; b = function(c, d = 2) { c }; b(a) }

fex = extractFunctions(f)

numTerms(f) - 16 numTerms(fex$new) 8 numTerms(fex$nested[[1]]) 6

g = function(x, y) { a = 1; b = function(c, d = 2) { c }; o = function() 10; b(a) }

gex = extractFunctions(g) numTerms(g) - 22 numTerms(gex$new) 8 numTerms(gex$nested[[1]]) 6 4 = 10

numTerms(f) ctr4 = CodeAnalysis:::mkCounter () walkCode(f, ctr4); ctr4$.els()

[[1]]

[[2]]

[[3]] {

[[4]] =

[[5]] a

[[6]] [1] 1

[[7]] =

[[8]] b

[[9]] function

[[10]]

[[11]] [1] 2

[[12]] {

[[13]] c

[[14]] function(c, d = 2) { c }

[[15]] b

[[16]] a

fex = extractFunctions(f) ctr4 = CodeAnalysis:::mkCounter () walkCode(fex$new, ctr4); ctr4$.els()

[[1]]

[[2]]

[[3]] {

[[4]] =

[[5]] a

[[6]] [1] 1

[[7]] b

[[8]] a

This corresponds to + the 2 parameters + { + a = 1 + b(a)

fex = extractFunctions(f) ctr4 = CodeAnalysis:::mkCounter () walkCode(fex$nested[[1]], ctr4); ctr4$.els()

[[1]] function

[[2]]

[[3]] [1] 2

[[4]] {

[[5]] c

[[6]] function(c, d = 2) { c }

This corresponds to 9..14 in the original function.

duncantl/CodeAnalysis documentation built on June 12, 2025, 6:44 a.m.