Define a primitive data type: Difference between revisions

=== Method 1: Safe Integer Store operators===

Forth is a fetch and store based virtual machine. If we create a safe version of store (!) the programmer simply uses this operator rather than the standard store operator.

: CLIP ( n lo hi -- n') ROT MIN MAX ;

: BETWEEN ( n lo hi -- flag) 1+ WITHIN ;

: SAFE! ( n addr -- )

OVER 1 10 BETWEEN 0= ABORT" out of range!"

Testing

7 X SAFE! X ? 7 ok

12 X CLIP! X ? 10 ok

$7FAA2B0C throw

$7FAD4698 c(abort")

=== Method 2: redefine standard "store" operator as DEFER word ===

Using the code in Method 1, we can re-define the store (!) operator to be switchable.

: FAST! ( n addr -- ) ! ; ( alias the standard version)

: LIMITS-ON ( -- ) ['] SAFE! IS ! ;

: LIMITS-OFF ( -- ) ['] FAST! IS ! ;

Testing

LIMITS-OFF ok

$7FAA2B0C throw

$7FAD4460 c(abort")

=== Method 3: Create a safe VALUE assignment operator===

A VALUE defines a numerical data type that returns it's value rather than an address (pointer) like a variable.

We can create a word that assigns a number to a VALUE but tests for out of range errors.

OVER 1 10 BETWEEN 0= ABORT" out of range!"

>BODY ! ;

IF POSTPONE ['] POSTPONE (->) \ compiling action

ELSE ' (->) \ interpret action

Test

99 TO Z ok ( normal assignment)

Z . 99 ok

$7FAA2B0C throw

$7FAD4570 c(abort")

=={{header|Fortran}}==