If all you care about is emulating static type checking, then you can also
accomplish the same thing with lambda.r using type constraints on function
definitions.
e.g.
> f(m) %::% matrix : matrix
> f(m) %as% { m }
> f(as.data.frame(matrix(rnorm(12),nrow=3)))
Error in UseFunction("f", ...) : No valid function for 'f(data.frame)'
> f(1)
Error in UseFunction("f", ...) : No valid function for 'f(1)'
> f
<function>
[[1]]
f(m) %::% matrix:matrix
f(m) %as% …
On Aug 20, 2013, at 4:36 PM, Peter Langfelder <peter.langfel...@gmail.com>
wrote:
> On Tue, Aug 20, 2013 at 11:41 AM, ivo welch <ivo.we...@anderson.ucla.edu>
> wrote:
>> I am using a variant of stopifnot a lot. can I suggest that base R
>> extends its functionality? I know how to do this for myself. this is
>> a suggestion for beginners and students. I don't think it would break
>> anything.
>>
>> first, I think it would be more useful if it had an optional character
>> string, so users could write
>>
>> stopifnot( is.matrix(m), "m is not a matrix" )
>>
>> this would mean that stopifnot would have to detect whether the last
>> argument is a string. (I think stopifnot should have had only one
>> condition, and one should have used all() to test multiple conditions,
>> but this is a bridge that was already crossed.) upon failure,
>> stopifnot should print the character string. that's it.
>>
>>
>> A second enhancement would be a "smart string", which knows that
>> everything inside {{...}} should be evaluated.
>>
>> stopifnot( is.matrix(m), "m is not a matrix, but a {{class(m)}}" )
>
> I think using a function (in this case paste) is cleaner:
>
> paste("m is not a matrix, but a", class(m))
>
> It avoids adding a new convention ("evaluate everything between {{
> }}") and has additional arguments.
>
>>
>>
>> my own programming variant looks even nicer,
>>
>> is.matrix(m) %or% "m is not a matrix but a {{class(m)}}"
>
> In R you can write it as
>
> is.matrix(m) || stop("m is not a matrix but a ", class(m))
>
> Examples:
>
> m = 1
>> is.matrix(m) || stop("m is not a matrix but a ", class(m))
> Error: m is not a matrix but a numeric
>
>> m = matrix(0,2,2)
>> is.matrix(m) || stop("m is not a matrix but a ", class(m))
> [1] TRUE
>
> But the construct
>
> if (!is.matrix(m)) stop("m is not a matrix but a ", class(m))
>
> is more readable for people not used to Pearl.
>
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