There is some strange formatting in this part of the Evaluation chapter (see below image). I think it is due to the sidebar styling.
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::: sidebar |
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**Expression vectors** |
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\index{expression vectors} |
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`base::eval()` has special behaviour for expression _vectors_, evaluating each component in turn. This makes for a very compact implementation of `source2()` because `base::parse()` also returns an expression object: |
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```{r} |
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source3 <- function(file, env = parent.frame()) { |
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lines <- parse(file) |
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res <- eval(lines, envir = env) |
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invisible(res) |
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} |
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``` |
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While `source3()` is considerably more concise than `source2()`, this is the only advantage to expression vectors. Overall I don't believe this benefit outweighs the cost of introducing a new data structure, and hence this book avoids the use of expression vectors. |
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::: |
