Re: [q-lang-users] newbie question on io, etc

[<Dr....@t-...>]

Following up to my earlier mail...

> But you also asked for an imperative solution. [...]

There also is a "real" imperative solution, with variable updates and 
all that nasty stuff, using Q's expression references (a.k.a. mutable 
values, cf. 12.13 in the manual). Here goes:

// additional control constructs

special when ~P X, loop P X;

when P X
	= X if P;
	= () otherwise;

loop P X
	= X || loop P X if P;
	= () otherwise;

// split data lines into (NAME,VAL) pairs

parse S	= (NAME,VAL) where (NAME,VAL) = sscanf S "%s %d"; // good value
	= (NAME,VAL) where (NAME,VAL) = sscanf S "%s %s"; // bad value
	= (NAME,"") where NAME:String = sscanf S "%s"; // missing value
	= () otherwise; // empty line

// the analysis program, imperative style

baz	= loop (not feof F)
	  (put LINENO (get LINENO+1) ||
	   match (parse (freads F))
	   (case () (), // skip empty lines
	    case (NAME,VAL)
	    (ifelse (isint VAL)
	     // update statistics
	     (when (eq () (get MIN_VAL) or else (get MIN_VAL>VAL))
	      (put MIN_VAL VAL || put MIN_NAME NAME) ||
	      when (eq () (get MAX_VAL) or else (get MAX_VAL<VAL))
	      (put MAX_VAL VAL || put MAX_NAME NAME) ||
	      put SUM (get SUM+VAL) || put COUNT (get COUNT+1))
	     // report bad value
	     (fprintf ERROR "bad value '%s' at line %d\n" (VAL,get LINENO))
	    ))) ||
	  // report results
	  ifelse (get COUNT>0)
	  (printf "min score == %d (%s)\nmax score == %d (%s)\n"
	   (get MIN_VAL,get MIN_NAME,get MAX_VAL,get MAX_NAME) ||
	   printf "avg score == %g\n" (get SUM/get COUNT))
	  (fwrites ERROR "no data\n")
	    where F:File = fopen "data.txt" "r",
	      LINENO = ref 0, SUM = ref 0, COUNT = ref 0,
	      MIN_NAME = ref (), MIN_VAL = ref (),
	      MAX_NAME = ref (), MAX_VAL = ref ();

Plain ugly, but as you can see it's possible. ;-) By adding some more 
control structures, one could easily embed a complete imperative 
sublanguage in Q, very much like those found in ML and Haskell (without 
the syntactic sugar). But I see no real point in doing so. Mutable 
values can occasionally be useful to speed things up, though. (Note that 
these aren't even in the core language, rather they are provided by the 
clib module.)

Albert

-- 
Dr. Albert Gr"af
Email:  Dr....@t-..., ag...@mu...
WWW:    http://www.musikwissenschaft.uni-mainz.de/~ag