explorations/modifyCode/Notes.md

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

Rewriting Code with codetools::walkCode()

The idea is to reassemble the language objects and collect information.

Examples of what we want to do are

• √ change a variable/parameter name and all of its uses.
• √ add an argument to specific calls
• √ remove calls, e.g.,
  • nested functions of the form fn = function()...
  • rewrite if(TRUE) ... else ... to remove the else ...
  • assignments to unused variables

These operations will allow us to implement

• constant propagation/replacement
• remove named nested functions and make them separate functions that can be reused and tested separately.
• identify which non-local variables they were accessing
• add corresponding parameters to these new functions
• arrange for calls to those functions in the original function to pass these non-local variables.

Moving Functions out of a Function

The following is a very simple example, intentionally so.

foo =
function(x, lambda = 2)
{
   alpha = lambda/nrow(x)

   do = function(val)
             val * alpha

   apply(x, 2, do)
}

We want to extract do as a separate function.

It needs alpha, so we would add that as an additional parameter. We write it as

do = function(val, alpha)
         val * alpha

Now, we need to add alpha in the calls to do. We'd rewrite foo as

foo =
function(x, lambda = 2)
{
   alpha = lambda/nrow(x)
   apply(x, 2, do, alpha)
}

A simpler version is when the original function calls the nested function directly.

foo =
function(x, lambda = 2)
{
   alpha = lambda/nrow(x)

   do = function(val)
             val * alpha

   a = do(x[, 1])
   b = sum(do(x[ !is.na(x[ ,2]), 2]))   
}

We would rewrite this as

foo =
function(x, lambda = 2)
{
   alpha = lambda/nrow(x)

   a = do(x[, 1], alpha)
   b = sum(do(x[ !is.na(x[ ,2]), 2], alpha))   
}

Todo

addParams

• [test] implement the changeParamName

• character vector of c(name = newName,...) and rewrite() like in propagate.R

• passGlobals

• rewrite calls to any of the new functions, adding the named arguments.

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