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Error Messages

C[[delete]](newfile) = let (k',p') = isempty(newfile) ->
    ("error: file is empty", newfile)
    [] ("", delete(newfile))
    in ("delete" concat k', p')
= let (k',p') = ("error: file is empty", newfile)
    in ("delete" concat k', p')
= ("delete" concat "error: file is empty", newfile)
= ("delete error: file is empty", newfile)

S[[C cr S]]

1. Evaluate C[[C]]p to obtain next log entry l' plus updated file p'.
2. Cons l' to log list and pass p' to S[[S]].
3. Evaluate S[[S]]p' to obtain meaning of rest of program i.e. rest of log output plus final version of file.