Modify an R function

Usage

ast_modify(x, from, to, if_many = "random", no_match = stop)

Arguments

x: an object of class ast
from: (character) character string to replace. note that we look for an exact match
to: (character) character string to put in place of from
if_many: (character) if multiple matches to the from parameter input, should we randomly select one to replace, replace the first instance, or replace all? one of: first, all, random
no_match: (function) how to deal with no matches. by default we stop(), but you can set to warning() or message()

Value

same as the input, an object of class ast, but modified

Details

we check that the from input has a match in the function data, if not, we fail out

Examples

foo <- function(x) {
  x + 1
}
foo(5)
#> [1] 6

# decompose the function
df <- ast_decompose(foo)
#> Error in as_string(x): Can't convert a logical vector to a string.
df
#> function (x, df1, df2, ncp, log = FALSE) 
#> {
#>     if (missing(ncp)) 
#>         .Call(C_df, x, df1, df2, log)
#>     else .Call(C_dnf, x, df1, df2, ncp, log)
#> }
#> <bytecode: 0x564bf3967008>
#> <environment: namespace:stats>
data.frame(df)
#> Error in as.data.frame.default(x[[i]], optional = TRUE): cannot coerce class ‘"function"’ to a data.frame
attr(df, "expr")
#> NULL

# modify an aspect of the function
out <- ast_modify(x = df, from = "+", to = "-")
#> Error: x must be of class ast
out
#> Error: object 'out' not found
class(out)
#> Error: object 'out' not found
attributes(out)
#> Error: object 'out' not found
data.frame(out)
#> Error: object 'out' not found
attr(out, "expr")
#> Error: object 'out' not found

# more examples
bar <- function(x) x / 6
(z <- ast_decompose(bar))
#> Error in as_string(x): Can't convert a logical vector to a string.
ast_modify(z, from = "/", to = "*")
#> Error: object 'z' not found

# to get the new function, pass through ast_recompose
b <- ast_modify(z, from = "/", to = "*")
#> Error: object 'z' not found
newbar <- ast_recompose(b, TRUE)
#> Error: object 'b' not found
bar(7)
#> [1] 1.166667
eval(newbar)(7)
#> Error: object 'newbar' not found

# multiple from matches
foo <- function(x) {
  w <- x + 1
  w + 5
}
foo(1)
#> [1] 7
x <- ast_decompose(foo)
#> Error in as_string(x): Can't convert a logical vector to a string.
(w <- ast_modify(x, "+", "-"))
#> Error: object 'x' not found
eval(ast_recompose(w, TRUE))(1)
#> Error: object 'w' not found

# if_many options
ast_modify(x, "+", "-", if_many = "random")
#> Error: object 'x' not found
ast_modify(x, "+", "-", if_many = "random")
#> Error: object 'x' not found
ast_modify(x, "+", "-", if_many = "random")
#> Error: object 'x' not found
ast_modify(x, "+", "-", if_many = "first")
#> Error: object 'x' not found
ast_modify(x, "+", "-", if_many = "all")
#> Error: object 'x' not found