[CakeML-dev] New string/bytearray operations

Magnus Myreen magnus.myreen at gmail.com
Mon Mar 20 06:32:53 UTC 2017

Sounds good to me. One thing to note: the semantics should read all
the values before writing them. This is so that we give the obviously
correct semantics to copying inside the same array. The implementation
will need to check whether it should do left-to-right or right-to-left
copying so that the code doesn't accidentally read from what it just

Also, as I pointed out in my other email, I think these memcpy
primitives should also exist for normal value arrays.


On 20 March 2017 at 06:29, Ramana Kumar <Ramana.Kumar at cl.cam.ac.uk> wrote:
> I've been rethinking these primitives after the discussion at the last
> hangout, and have come up with a different set altogether. Can you see a
> simpler or more elegant approach to the one described below?
> Here is the new approach I am considering:
> 4 copying primitives in the source language going from string/bytearray to
> string/bytearray.
> The source comes with an offset and a length to copy.
> If the destination is a string, a new string is created. If the destination
> is a bytearray, it must be provided.
> Concatenation (of lists of strings/arrays) and conversions between (whole)
> strings and (whole) bytearrays can be implemented in the basis library in
> terms of these primitives. And the primitives should be efficiently
> implementable in terms of a byte-based memcpy primitive further down. (There
> will need to be bounds checking in the source-level semantics (i.e.,
> Subscript exception can be raised), and this will sometimes be unfortunate
> (i.e., when obviously in bounds), but I don't think this is too costly.)
> On 14 March 2017 at 16:52, Ramana Kumar <Ramana.Kumar at cl.cam.ac.uk> wrote:
>> Hi all,
>> I've started adding string/bytearray conversion and concatenation
>> primitives (issues 244 and 245). Before getting too deep into updating
>> the compiler etc., may I request a review of the semantics? Here they
>> are:
>> https://github.com/CakeML/cakeml/commit/67dd15bbd03f516be618ba72f1d56a2764209263
>> I noticed that v_to_char_list might be better as vs_to_char_list, to
>> be run after v_to_list (rather than duplicating its
>> list-deconstruction functionality). But I leave such refactoring for
>> another time.
>> Cheers,
>> Ramana
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