The following gives an error
test <- df <- data.frame(x=1:10, y=11:20)
test[] <- lapply(df, factor)
Error in "[<-.data.frame"(*tmp*, , value = lapply(df, factor)) : 
        Argument "i" is missing, with no default
It is correct S code, and works in S+3.4 and 6.0.
--please do not edit the information below--
Version:
 platform = i686-pc-linux-gnu
 arch = i686
 os = linux-gnu
 system = i686, linux-gnu
 status = 
 major = 1
 minor = 3.0
 year = 2001
 month = 06
 day = 22
 language = R
Search Path:
 .GlobalEnv, package:ctest, Autoloads, package:base
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