On Saturday, January 13, 2018 at 8:56:02 AM UTC-6, gmhwxi wrote:
>
> I can only outline a way in ATS that more or less matches
> the printf example in your message. In ATS, the function PrintfType
> can not be defined.
>
> On the other hand, if I understand correctly, your printf code in Idris
> would
> not be so easy to use if the format string is not a constant. For instance,
> I remember seeing an example in K&R where the format string is constructed
> at run-time.
>
Although I'm not sure how it works under the hood, the Idris example does
work with run-time constructed strings. That was originally what I was
trying to figure out: whether the strict separation between statics and
dynamics in ATS made this approach constant-only. But then I couldn't
figure out how to translate the example.
Since PrintfType can't be an ATS function, is there a more canonical way to
do a function like this printf thing in ATS? Or is this just a current
limitation of the language?
>
> abstype string(string)
> abstype format(string)
>
> datatype
> Format(type) =
> |
> {a:type}
> Number(int -> a) of Format(a)
> |
> {a:type}
> Str(string -> a) of Format(a)
> |
> {a:type}
> Lit(a) of (String, Format(a))
> |
> End(string) of ()
>
> extern
> fun
> toFormat
> {cs:string}
> (string(cs)): Format(format(cs))
>
> extern
> fun
> printfFmt
> {a:type}
> (fmt: Format(a), acc: string): a
>
> extern
> fun
> printf
> {cs:string}(fmt: string(cs)): format(cs)
>
> implement
> printf(fmt) = printfFmt(toFormat(fmt), "")
>
>
>
>
> On Friday, January 12, 2018 at 11:02:45 PM UTC-5, Max Hayden Chiz wrote:
>>
>>
>>
>> On Friday, January 12, 2018 at 8:15:54 PM UTC-6, gmhwxi wrote:
>>>
>>>
>>> >>But I assume you mean more generally that the idea of having a
>>> variadic function and parsing the first argument to determine the number of
>>> additional arguments and their types wasn't useful.
>>>
>>> It may be useful. But using %s for string, %c for char, etc. does not
>>> look like a good design.
>>>
>>> >>Is the variadic function capability what is missing in ATS2? If not,
>>> what is the difference that ATS1 allows it and ATS2 doesn't?
>>>
>>> Variadic functions are supported in ATS2.
>>>
>>
>> I was under the impression that they could be *called* but not *created*
>> as part of ATS2, i.e., I couldn't *make* my own variadic function. If that
>> not right, could you link to an example of how to make one in ATS?
>>
>>
>>> To support printf, one needs to parse a constant format string. I did
>>> not implement such a parser in ATS2.
>>>
>>
>> What I'm trying to understand is whether this is something that *hasn't*
>> been done or something that *can't* be done (short of modifying the
>> compiler). And again, this is just a toy example to help me understand how
>> ATS differs from Idris. I'm not trying to make the real printf type-safe or
>> make a good design for a printing library. I'm just trying to translate an
>> Idris example into ATS so that I can better understand the ATS language.
>>
>> I'll provide the Idris code below. I want to know if it's possible to do
>> something similar in ATS and whether it would work with a run-time supplied
>> format string or if it would only work for compile-time constants.
>>
>> The way this works in Idris is as follows:
>>
>> data Format = Number Format
>> | Str Format
>> | Lit String Format
>> | End
>>
>> PrintfType : Format -> Type
>> PrintfType (Number fmt) = (i : Int) -> PrintfType fmt
>> PrintfType (Str fmt) = (str : String) -> PrintfType fmt
>> PrintfType (Lit str fmt) = PrintfType fmt
>> PrintfType End = String
>>
>> printfFmt : (fmt : Format) -> (acc : String) -> PrintfType fmt
>> printfFmt (Number fmt) acc = \i => printfFmt fmt (acc ++ show i)
>> printfFmt (Str fmt) acc = \str => printfFmt fmt (acc ++ str)
>> printfFmt (Lit lit fmt) acc = printfFmt fmt (acc ++ lit)
>> printfFmt End acc = acc
>>
>> toFormat : (xs : List Char) -> Format
>> toFormat [] = End
>> toFormat ('%' :: 'd' :: chars) = Number (toFormat chars)
>> toFormat ('%' :: 's' :: chars) = Str (toFormat chars)
>> toFormat ('%' :: chars) = Lit "%" (toFormat chars)
>> toFormat (c :: chars) = case toFormat chars of
>> Lit lit chars' => Lit
>> (strCons c lit) chars'
>> fmt => Lit (strCons c "") fmt
>>
>> printf : (fmt : String) -> PrintfType (toFormat (unpack fmt))
>> printf fmt = printfFmt _ ""
>>
>> Thank you for your help.
>>
>>
>>
>>
>>> On Friday, January 12, 2018 at 7:49:45 PM UTC-5, Max Hayden Chiz wrote:
>>>>
>>>> Thank you again for your reply.
>>>>
>>>> On Friday, January 12, 2018 at 5:42:09 PM UTC-6, gmhwxi wrote:
>>>>>
>>>>> ATS1 and ATS2 are very similar modulo minor syntactic differences.
>>>>> There isn't really much point in learning ATS1.
>>>>>
>>>>> I did not implement the printf stuff in ATS2 because it was not
>>>>> particularly
>>>>> useful.
>>>>>
>>>>
>>>> I agree that printf isn't particularly useful, it was just a toy
>>>> example that I was playing with.
>>>>
>>>> But I assume you mean more generally that the idea of having a variadic
>>>> function and parsing the first argument to determine the number of
>>>> additional arguments and their types wasn't useful.
>>>>
>>>>
>>>>> I have to say that 'printf' was a poor idea to start with in the first
>>>>> place.
>>>>> There are a lot more types than letters.
>>>>>
>>>>> >> So printf "%c %f" is of type "Char -> Double -> String"
>>>>>
>>>>> By the say, this is not true printf. The printf supported in ATS1 is a
>>>>> variadic function
>>>>> (just like in C).
>>>>>
>>>>
>>>> Is the variadic function capability what is missing in ATS2? If not,
>>>> what is the difference that ATS1 allows it and ATS2 doesn't?
>>>>
>>>>
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