TOPS-20 PASCAL Language Manual - Bitsavers

PROCEDURES AND FUNCTIONS
In the main program, the WHILE loop reads a number and a name for one
student. The following procedure call allocates memory for a new
student record:
NEW (!3tudent) ;
The new record is inserted at the beginning of the list, that is,
StudentA.Next points to the previous head of the list. The value of
the new student record is assigned to the Start pointer.
The WRITE DATA procedure writes the name and student ID number for
each stu~ent in the linked list. After writing data for one student,
the procedure assigns the address of the next record in the list to
Next Student. The following call deallocates memory for one student
record:
11 I SPOS[ (Sturjf.~nt) ;
After deallocating memory, the procedure assigns the value of
Next Student to Student. When the current student record points to
NIL, the loop stops executing.
NEW AND DISPOSE -- RECORD-WITH-VARIANTS FORM
You can use the following forms of NEW and DISPOSE when manipulating
dynamic variables of a record type with variants:
N EW ( p , t 1 , . • • , t n )
DISPOSE(p,tl, ••. ,tn)
The parameter p must be a pointer variable pointing
variants. The optional parameters tl through
constants. They represent nested tag field values
outermost variant.
to a record with
tn must be scalar
where tl is the
If you create p without specifying the tag field values, the system
allocates enough memory to hold any of the variants in the recard.
Sometimes, however, a dynamic variable takes values of only a
particular variant. If that variant requires less memory than NEW(p)
allocates, you should use the NEW(p,tl, ••. ,tn) form.
For example, the following record represents a menu selection:
TYPE Menu_Ptr = ~Menu_Order;
Meat_T~pe = (Fish, Fowl, Beef);
Beef _Po rt i on ;:;; «()z _.. 10, Oz_ .. 16, Oz_32);
Menu_Order = RECORD
CASE Entree : Meat_T~pe OF
Fish ( F i S tL T ~ P f.~ : ( S a 1m 0 n, Cod, P (-? r c h, T T' out ) ;
Lemon: BOOLEAN);
Fowl (Fowl_T~pe : (Chicken, Duck, Goose);
Sauce: (Orange, Cherr~, Raisin»;
Beef ( Bee f._ T y p e : ( S tea k, R 0 a~; t, P rim e _.. rib) ;
CASE Size : Beef_Portion OF
Oz_.10, Oz_:L6 : (BeeL.. vf?~.:j : (AT'tichoke, ML·~ed»;
Oz_32 : (Stomach_Cure : (Bicarbonate,
Antacid,None_Needed»;
END;
VAR Menu_Selection
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