Reva: Tips and Tricks

Using singles and doubles
If you use a word which expects a 'double' on the stack, you need to ensure you actually have a double on the stack! For example, 1 d. will not print 1! Instead, you must do one of the following:

1 s>d d.


1L d.

Enter dates as if they were numbers
This can be done by assigning your own handler to word?. See "numberparse.f" in the examples directory for how it's done.

Recursion in Reva
To have a word call itself, simply use the name of the word inside the body. Unlike ANS Forths, Reva does not "smudge" the dictionary while defining a word. This allows you to easily recurse, as the following silly example shows:

 : my-word ." Going to recurse ..." my-word ;

"Subclassing" a word
As the previous tips showed, Reva does not call the previous definition of a word if you invoke its name while it is being redefined. If, however, you do want to do that, simply use the word prior:

 : my-word ." Going to call previous version ..." prior my-word ;

If you want to call the previous value of a deferred word, you need to use chain:

 :: dup . chain emit ; is emit

Cleanup on application shut-down
There are two ways to do this:

  1. Assign your own word to bye (which is deferred).
  2. Use the onexit word. Here is an example of the second technique:
      3 variable, countdown
      noname: countdown @ dup 0; 1- countdown ! ." Not yet..." cr r> drop ;
        Not yet!
        Not yet!
        Not yet!

After the last bye you will leave Reva. Note the r> drop trick, which makes you leave the calling word! This is a way to keep from calling (bye) which is the os-specific implementation of bye.

How to get double-quotes in a string
Reva borrows a trick from the "C" family of languages - you "escape" a character by preceding it with a backslash. So:

" \"Mary!\", her mother said, \"Come in for dinner!\""

Results in: "Mary!", her mother said, "Come in for dinner!".