> 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?
>
Given the design of ATS, I see it as a fundamental limitation of ATS.
But useful systems all have limitations :)
If I am to support 'printf', I would only handle constant format strings.
Then
I can write a parsing function parseFmt externally. Then I can write code
like
val () = printf(##parseFmt("x(int) = %i and y(string) = %s"), 1, "A")
On Saturday, January 13, 2018 at 11:59:38 AM UTC-5, Max Hayden Chiz wrote:
>
>
>
> 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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