[clean-list] term reading and writing

[Thomas van Noort]

Hi,

The Generics library, provided in the Clean distribution, contains two 
modules which define exactly the functions you require.

HP Wei wrote:
> Newbie questions--
> 
> Suppose there is a data type,
> 
> :: Person = { name :: String,
>               id :: (Int, String),
>               flag :: Bool }
> 
> Suppose a file whose name is fname.txt 
> has the following content:
> { name = "a_name",
>   id = (123, "an_id"),
>   flag = True }
> 
> -----------------------------------
> Q1: how do I 'read in' a Person from fname.txt ?
>    [ i.e.
>      If person is of type Person,
>      person = _read_ "fname.txt"
> 
>    is there a built-in fx that does the above _read_ ?
>    Or shall I need to write a parse-fx to do this ?

Import the module GenParse from the Generics library and use the 
function parseFile,

parseFile :: File -> Maybe a | gParse{|*|} a

which requires you to derive an instance of gParse for Person,

derive gParse Person

> 
> Q2: if person = {name ="xyz",
>                  id = (456, "id"),
>                  flag = False}
> 
>     how do I _print_ this 'person' to a text file
>     fname1.txt ?

Import the module GenPrint from the Generics library and use the 
function printToString,

printToString :: a -> String | gPrint{|*|} a

which requires you to derive an instance of gPrint for Person,

derive gPrint Person

The function returns a String but you can easily define a function 
yourself which prints to a file,

printToFile :: a File -> File | gPrint{|*|} a

> 
> *** for those who knows Erlang, Q1 and Q2 are term 
>     reading and writing.
> 
> THanks
> HP
> 
> 
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Regards,
Thomas