“Maybe there’s a better example of the compile time check of the stack effect declaration? Or am I missing something?”
— Jon

Yeah, sorry about that. When developing in Factor, it’s standard practice to use an external text editor, and hit F2 in the listener to reload your vocabulary (a collection of words in a file) whenever you make changes. I plan on discussing that process in more detail later, but forgot about the differences when pasting code directly in the listener.

Just follow what Slava says…pretty much always

However, even for words defined in the listener, you can still do:

[ plus-two ] infer.

which in your case would display an error about the stack declaration mismatch.

: plus-two ( -- y ) 2 + ;

… and I got no warning. When I did “\ plus-two see”, I got the same thing back. And doing “4 plus-two” I got 6. Maybe there’s a better example of the compile time check of the stack effect declaration? Or am I missing something?

“Is there a compile time check whether the word stack effects declaration matches the code?”
– wolf550e

Yes, there is a check…if what the compiler infers does not match the stack effect declaration, it will generate an error. If we had left off the “x” in our declaration of plus-two, the error generated would look something like this:

In word: plus-two
Stack effects of the word plus-two do not match.
Inferred: (( object -- object ))
Declared: (( -- y ))

To read more about stack effect inference, type "inference" help into the listener…