Wrap a function for debugging.

Source: R/DebugFn.R

Wrap fn, so it will save arguments on failure.

DebugFnW(saveDest, fn)

Arguments

saveDest

where to write captured state (determined by type): NULL random temp file, character temp file, name globalenv() variable, and function triggers callback.
fn

function to call

Value

wrapped function that saves state on error.

See also

dump.frames, DebugFn, DebugFnW, DebugFnWE, DebugPrintFn, DebugFnE, DebugPrintFnE Operator idea from: https://gist.github.com/nassimhaddad/c9c327d10a91dcf9a3370d30dff8ac3d . Please see: vignette("DebugFnW", package="wrapr").

Examples


saveDest <- paste0(tempfile('debug'),'.RDS')
f <- function(i) { (1:10)[[i]] }
df <- DebugFnW(saveDest,f)
# correct run
df(5)

#> [1] 5
# now re-run
# capture error on incorrect run
tryCatch(
   df(12),
   error = function(e) { print(e) })

#> <simpleError in value[[3L]](cond): wrapr::DebugFnW: wrote '/var/folders/7f/sdjycp_d08n8wwytsbgwqgsw0000gn/T//RtmpupYvzx/debug13dd0464965e5.RDS' on catching 'Error in (1:10)[[i]]: subscript out of bounds'
#>  You can reproduce the error with:
#> 'p <- readRDS('/var/folders/7f/sdjycp_d08n8wwytsbgwqgsw0000gn/T//RtmpupYvzx/debug13dd0464965e5.RDS'); do.call(p$fn, p$args)'>
# examine details
situation <- readRDS(saveDest)
str(situation)

#> List of 4
#>  $ fn       :function (i)  
#>   ..- attr(*, "srcref")= 'srcref' int [1:8] 3 6 3 32 6 32 3 3
#>   .. ..- attr(*, "srcfile")=Classes 'srcfilecopy', 'srcfile' <environment: 0x7fc751dae828> 
#>  $ args     :List of 1
#>   ..$ : num 12
#>  $ namedargs: language df(12)
#>  $ fn_name  : chr "f"
# fix and re-run
situation$args[[1]] <- 6
do.call(situation$fn,situation$args)

#> [1] 6
# clean up
file.remove(saveDest)

#> [1] TRUE


f <- function(i) { (1:10)[[i]] }
curEnv <- environment()
writeBack <- function(sit) {
   assign('lastError', sit, envir=curEnv)
}
attr(writeBack,'name') <- 'writeBack'
df <- DebugFnW(writeBack,f)
tryCatch(
   df(12),
   error = function(e) { print(e) })

#> <simpleError in value[[3L]](cond): wrapr::DebugFnW: wrote error to user function: 'writeBack' on catching 'Error in (1:10)[[i]]: subscript out of bounds'
#>  You can reproduce the error with:
#>  'do.call(p$fn, p$args)' (replace 'p' with actual variable name)>
str(lastError)

#> List of 4
#>  $ fn       :function (i)  
#>   ..- attr(*, "srcref")= 'srcref' int [1:8] 22 6 22 32 6 32 22 22
#>   .. ..- attr(*, "srcfile")=Classes 'srcfilecopy', 'srcfile' <environment: 0x7fc7521576d0> 
#>  $ args     :List of 1
#>   ..$ : num 12
#>  $ namedargs: language df(12)
#>  $ fn_name  : chr "f"