XML CO538 Anonymous Questions and Answers Keyword Index

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Keyword reference for record-types

Question 84 (2003):

In our seminar we were given the syntax to (a) create our own data type which is usefull for the coordinates and (b) fill the data type with values.

I can create my own data type with no trouble, but assigning a data type of:

    DATA TYPE COORDS
      RECORDS
        INT x,y:
    :

the way we were shown:

    [5] COORDS phil.pos[[*,*],[*,*],[*,*],[*,*],[*,*]]: (with the * as INT's)

doesn't work - I have tried messing about to get it to work but to no avail. Any obvious problems with this syntax?

Answer 84:

The syntax is nearly there, but not quite. Constants in occam aren't like variables; they're constants, not variables that you can't assign/input to. Thus the declaration of these is slightly un-expected. As a minor point, `RECORDS' in your data-type definition should just be `RECORD'.

The correct way to declare a set of constant co-ordinates (using your record type) would be:

    VAL []COORDS phil.pos IS [[*,*], [*,*], ...]:

You don't need to give the array-dimension explicitly here -- the compiler can count the number of things on the right-hand side.

If, however, you want to change these values as the program runs, you'd need a real variable array:

    [5]COORDS phil.pos:
    SEQ
      phil.pos := [[*,*], [*,*], ...]

.. or the shorter way using an INITIAL declaration.

See also the answer to Question 68 (2000).

Keywords: record-types , table

Question 45 (2002):

What is a RECORD used for?

Answer 45:

This is not examinable. See:

  \\raptor\files\courses\co516\etc\records.txt

if you want some information.

Keywords: record-types

Referrers: Question 44 (2002)