# PL_TDF Definition

### January 1998

4.1 - Sieve of Erastothenes
4.2 - Example with structures
4.3 - Test for case
4.4 - Example of use of high-order TOKENs
4.5 - A test for long jumps

# 4 Example PL_TDF programs

## 4.1. Sieve of Erastothenes

```	/* Print out the primes less than 10000 */
String s1 = "%d\t";					/* good strings for printf */
String s2 = "\n";

Var n: nof(10000, Char);					/* will contain1 for prime; 0 for composite */

Tokdef N = [ind:EXP]EXP n *+. (Sizeof(Char) .* ind);
/* Token delivering pointer to element of n */

Iddec printf : proc;				/* definition provided by ansi library */

Proc main = top ()
Var i:Int
Var j:Int
{ Rep (i = 2(Int))
{ 	/* set i-th element of n to 1 */
N[* i] = 1(Char);
i = (* i + 1(Int));
?(* i >= 10000(Int))			/* NB assertion fails to continue loop */
}
Rep (i = 2(Int) )
{
?{ 	?( *(Char)N[* i] == 1(Char));
/* if its a prime ... */
Rep ( j = (* i + * i) )
{ /*... wipe out composites */
N[* j] = 0(Char);
j = (* j + * i);
?(* j >= 10000(Int))
}
| make_top
};
i = (* i + 1(Int));
?(* i >= 100(Int))
};
Rep (i = 2(Int); j = 0(Int) )
{ 	?{ 	?( *(Char)N[* i] == 1(Char));
/* if it's a prime, print it */
printf[top](s1, * i);
j = (* j + 1(Int));
?{ 	?( * j == 5(Int));
/* print new line */
printf[top](s2);
j = 0(Int)
| make_top
}
| make_top
};
i = (* i + 1(Int));
?(* i >= 10000(Int))
};
return(make_top)
};

Keep (main)			/* main will be an external name; so will printf since it is not defined */
```

## 4.2. Example with structures

```	Struct C (re:Double, im:Double);
/* define TOKENs : C as a SHAPE for complex, with field offsets .re and .im
and selectors re and im */

Iddec printf:proc;

Proc addC = C (lv:C, rv:C) 					/* add two complex numbers */
Let l = * lv
Let r = * rv
{ return( Cons[shape_offset(C)] ( .re: re[l] F+ re[r], .im: im[l] F+ im[r]) ) } ;

String s1 = "Ans = (%g, %g)\n";

Proc main = top()
Let x = Cons[shape_offset(C)] (.re: 1.0(Double), .im:2.0(Double))
Let y = Cons[shape_offset(C)] (.re: 3.0(Double), .im:4.0(Double))
Let z = addC[C](x,y)
{	printf[top](s1, re[z], im[z]);
/* prints out "Ans = (4, 6)" */
return(make_top)
};

Keep(main)
```

## 4.3. Test for case

```	Iddec printf:proc;

String s1 = "%d is not in [%d,%d]\n";
String s2 = "%d OK\n";

Proc test = top(i:Int, l:Int, u:Int)					/* report whether l<=i<=u */
?{ 	?(* i >= * l); ?(* i <= * u);
printf[top](s2, * i);
return(make_top)
| 	printf[top](s1, * i, * l, * u);
return(make_top)
};

String s3 = "ERROR with %d\n";

Proc main = top()				/* check to see that case is working */
Var i:Int = 0(Int)
Rep {
Labelled {
Case * i (0 -> l0, 1 -> l1, 2:3 -> l2, 4:10000 -> l3)
| :l0: test[top](* i, 0(Int), 0(Int))
| :l1: test[top](* i, 1(Int), 1(Int))
| :l2: test[top](* i, 2(Int), 3(Int))
| :l3: printf[top](s3, * i)
};
i = (* i + 1(Int));
?(* i > 3(Int));
return(make_top)
};

Keep (main, test)
```

## 4.4. Example of use of high-order TOKENs

```	Tokdef IF = [ boolexp:TOKEN[LABEL]EXP, thenpt:EXP, elsept:EXP] EXP
?{ boolexp[lab]; thenpt | :lab: elsept };
/* IF is a TOKEN which can be used to mirror a standard if ... then ... else
construction; the boolexp is a formal TOKEN with a LABEL parameter
which is jumped to if the boolean is false */

Iddec printf: proc;

String cs = "Correct\n";
String ws = "Wrong\n";

Proc main = top()
Var i:Int = 0(Int)
{
IF[ Use [l:LABEL]EXP ?(* i == 0(Int) | l), printf[top](cs), printf[top](ws) ];
/* in other words if (i==0) printf("Correct") else printf("Wrong") */
IF[ Use [l:LABEL]EXP ?(* i != 0(Int) | l), printf[top](ws), printf[top](cs) ];
i = IF[ Use [l:LABEL]EXP ?(* i != 0(Int) | l), 2(Int), 3(Int)];
IF[ Use [l:LABEL]EXP ?(* i == 3(Int) | l), printf[top](cs), printf[top](ws) ];
return(make_top)
};

Keep (main)
```

## 4.5. A test for long jumps

```	Iddec printf:proc;

Proc f = bottom(env:pointer(frame_alignment), lab:pointer(code_alignment) )
{
long_jump(* env, * lab)
};

String s1 = "Should not reach here\n";
String s2 = "long-jump OK\n";

Proc main = top()
Labelled{
f[bottom](current_env, make_local_lv(l));
printf[top](s1);			/* should never reach here */
return(make_top)
| :l:
printf[top](s2);
return(make_top)
};

Keep (main)
```

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