Question

I need to read file in ML (SLMNJ) and save it in some structures. I need to read some data that points to graph declaration:

[( 1 , 2 , 13 ),( 2 , 3 , 3 ),( 2 , 4 , 8 ),( 2 , 5 , 4 ),( 3 , 1 , 5 ),( 3 , 4 , 1 ),( 4 , 6 , 5 ),( 5 , 5 , 5 ),( 6 , 4 , 6 )]

(first number: name of the node , secend number: name of connected node , third number weight for this mane (each () show one mane ) )

for expamle this is test input how to read file and which structure to save it

Answer 1

for reading from file follow this to list of string per line :

val infile = "c:/input.txt" ;

fun readlist (infile : string) = let 

  val ins = TextIO.openIn infile 

  fun loop ins = 

   case TextIO.inputLine ins of 

      SOME line => line :: loop ins 

    | NONE      => [] 

in 

  loop ins before TextIO.closeIn ins 

end ;

val pureGraph =  readlist(infile);

and with this function you can parse it to tuple (x,y,z ) :

fun creatGraph([],reList) = reList

|creatGraph(x::y::z::input,reList) =  creatGraph(input,reList@[(x,y,z)]);

Answer 2

This problem is perfectly suited to parsing combinators, which you can steal from my friend Greg Morrisett at Harvard.

If you want to understand the underlying ideas, read Graham Hutton s paper Higher-Order Functions for Parsing. If you want to know how to implement I/O in Standard ML, consult the TextIO module in the Standard Basis Library. If you want someone to write the code for you, you may have reached the wrong web site.

友情链接