Category : Files from Magazines
Archive   : MAR93.ZIP
Filename : PROXY.ASC

_PROXY: A SCHEME-BASED PROTOTYPING LANGUAGE_
by Burt Leavenworth

[LISTING ONE]

class queue(;rep) {
queue() {rep=[];}
enqueue(x) {rep=rep conc [x];}
dequeue(;x) {x=hd rep;
rep=tl rep;
return x;}
empty() {return rep==[];}};



LISTING TWO.

class pqueue(;rep) {
pqueue() {rep=[];}
private: insrt(x,y) {if(y == []) {rep = [x]; return rep;} else
if(x < hd y) {rep = [x] conc y;return rep;} else
{rep = [hd y] conc insrt(x,tl y);
return rep;}}
public: insert(x) {rep = insrt(x,rep); return rep;}
remove(;x) { if(rep == []) return "queue empty";
x = hd rep; rep = tl rep; return x;} };


[LISTING THREE]

add_mod(m,ms) {xu[m]=ms;};

del_mod(m) {xu= {x->xu[x] diff {m}:x <- (dom xu diff {m})};};

uses(m) {return xu[m];};

used_by(m) {return {ms:ms<-dom xu;m in xu[ms]};};

rec_mod() {return {m:m<-dom xu;reaches(m,m)};};

reaches(m1,m2) {return ((m2 in xu[m1])||(exists m in xu[m1];reaches(m,m2)));};


[LISTING FOUR]

add_mod("mod2",{"mod4","mod5","mod2"});
add_mod("mod3",{"mod5"});
add_mod("mod4",{"mod1","mod2"});
add_mod("mod5",{});
add_mod("mod1",{"mod2","mod3"});

xu = {"mod2"->{"mod4","mod5","mod2"},"mod3"->{"mod5"},
"mod4"->{"mod1","mod2"},"mod5"->{},"mod1"->{"mod2","mod3"}}

uses("mod1") returns {"mod2","mod3"}
used_by("mod2") returns {"mod2","mod4","mod1"}
rec_mod() returns {"mod2","mod4","mod1"}

del_mod("mod3");

xu = {"mod2"->{"mod4","mod5","mod2"},"mod4"->{"mod1","mod2"},
"mod5"->{},"mod1"->{"mod2"}}



Example 1. A general form for constructing sets.

{ f(x): x<- expr ; pred(x) }


Example 2. General method for constructing sets.

{ x: x<- {1,2,3,4,5}}; returns {1,2,3,4,5}

{ x: x <- {1,2,3,4,5};x>2}; returns {3,4,5}

{ x*x: x <- {1,2,3,4,5}}; returns {1,4,9,16,25}

It is possible to have two generators in which case an example is:

{ x+y: x <- {1,2}, y <- {3,4}} returns {4,5,6}


Only three elements are returned because two additions (1+4) and (2+3)
yield duplicate values.


Example 3: Syntax for using maps.

m = {1->2,3->4,5->6};


Example 4: (a) Domain restriction and subtraction; (b) using the
overwrite operator

(a)

{1->2,3->2,5->6} dr {3,5}; returns {3->2,5->6}
{1->2,3->2,5->6} ds {3,5}; returns {1->2}


(b)

{1->2,3->4} overwr {3->5,4->6}; returns {1->2,3->5,4->6}


Example 5a. General form for constructing a sequence; b)
constructing the sequence [4,5].

a)

[ f(x): x<- expr ; pred(x) ]

b)

[len x: x<-["abc","defg","hijkl"];len x > 3]; returns [4,5]



Example 6: (a) Syntax for the struct declaration; (b) Assigning
values to fileds in a struct

(a)

struct item {partno, code, quantity;};

(b)

i1.quantity=22; assigns 22 as the new value of the quantity field.