[Haskell-cafe] http://www.cs.cornell.edu/icfp/task.htm

Hauschild, Klaus (EXT) klaus.hauschild.ext at siemens.com
Mon Feb 28 09:37:05 CET 2011

Hi Thu,

You read my mind. Ok, for the details. Here are my data structur for the differen tokens (currently not complete):

data GmlToken =       IntToken Int
    | RealToken Double
    | BoolToken Bool
    | StringToken String
    | FunctionToken TokenSequence
    | ArrayToken TokenSequence
    | BinderToken String
    | IdentifierToken String
    | AddiToken

type TokenSequence  = [GmlToken]
type TokenStack     = [GmlToken]

Now I'm working on the tokenize method. There a public and a private version (indicated by ')

tokenize :: String →  TokenSequence
-- foreward to intern method
tokenize program = tokenize' (words program) []

tokenize' :: [String] → TokenSequence →  TokenSequence
-- last recursion step
tokenize' [] tokens
    = tokens
-- "addi" is a reserved keyword for the AddiToken
tokenize' ("addi" : words) tokens
    = tokenize' words (AddiToken : tokens)
-- binder tokens start with '/'
tokenize' (('/' : binder) : words) tokens
    = tokenize' words ((BinderToken binder) : tokens)
-- if nothing matches it is an identifier
tokenize' (name : words) tokens
    = tokenize' words ((IdentifierToken name) : tokens)

With this code I'm able to tokenize the different reserved keywords of the GML language, binder and identifier (these two handle variable access).
Now the problem: How to write the code to tokenize numbers (integer and double) and arrays and functions. I hope it is clear what is meant with numbers. Arrays and functions are embedded token sequences enclosed by "[" and "]" or "{" and "}".
Some examples:

tokenize' ["2", "2", "addi"] [] results in [IntToken 2, IntToken 2, AddiToken]
tokenize' ["2.0", "2.0", "addi"] [] results in [RealToken 2.0, RealToken 2.0, AddiToken]

tokenize' ["[", "foo", "/bar", "]"] results in [ArrayToken [IdentifierToken "foo", BinderToken "bar"]]

tokenize' ["{", "foo", "/bar", "}"] results in [FunctionToken [IdentifierToken "foo", BinderToken "bar"]]

-----Ursprüngliche Nachricht-----
Von: Vo Minh Thu [mailto:noteed at gmail.com] 
Gesendet: Freitag, 25. Februar 2011 17:44
An: Hauschild, Klaus (EXT)
Cc: haskell-cafe at haskell.org
Betreff: Re: [Haskell-cafe] http://www.cs.cornell.edu/icfp/task.htm

2011/2/25 Hauschild, Klaus (EXT) <klaus.hauschild.ext at siemens.com>:
> Hi,
> Currently I'm trying to lern Haskell by doing. After doing some examples I
> plan to solve an ICFP task (see subject). In short: build an interpreter for
> a stack based language thata describes a 3D scene. Ray trace this scene in
> an image. My current source state can be found here:
> http://code.google.com/p/hgmltracer/source/browse/
> My first goal is to develop the interpreter of the GML language. My source
> contains a data GmlToken with various constructors for the different
> operators, sequences, int, real, string an so on. Some code for the
> evaluation is also there und working.
> But the parser converting a string (contained in the program file provided
> as command line argument) is hard stuff and I'm stuck.
> Can any one help me with ideas or concepts for this parser?


You have chosen to develop a very interesting program and I'm sure a
lot of people could help you if you face any problem. But it would be
easier for those people to help you if you could be a bit more
specific about what works (or what you understand) and where you have
some problem.

In this case, maybe you could copy in the mail some code (possibly
cutting it down to what really matter).

For instance, I think central to your mail is this data structure:

data GmlToken =
      IntToken Int
    | RealToken Double
    | BoolToken Bool
    | StringToken String
    | FunctionToken [GmlSequence]
    | ArrayTokenToken [GmlSequence]
    | BinderToken String
    | IdentifierToken String
    | AddiToken

and the function

parse :: [String] -> TokenSequence -> TokenSequence
parse = ...

At first view I would say that parse should be (and I call it tokenize)

tokenize :: String -> [GmlToken]

Now, maybe you can provide some sample inputs *with* their expected
output and tell us what is really a problem for you.

Alternatively I can assume too much (or not enough) things from your
mail and you can enlighten me :)


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