subvergeStack
Each tab has one data stack. Words take their arguments from it and leave their results on it, and it is the only way to pass values between words.
Pushing and popping
1 2 3
+
Literals are pushed on top. + pops 3 and 2 and pushes 5, leaving 1 5. A word that finds too few values fails.
Stack effects
( a b -- c )
A stack effect lists what a word takes and what it leaves, with the top of the stack on the right. dup is ( a -- a a ). 'word help shows the effect of any word.
Stack words
| Word | Effect | |
|---|---|---|
dup |
a -- a a |
copies the top value |
drop |
a -- |
discards it |
swap |
a b -- b a |
swaps the top two |
over |
a b -- a b a |
copies the second to the top |
rot |
a b c -- b c a |
moves the third to the top |
nip |
a b -- b |
drops the second |
depth |
-- n |
the number of values |
empty |
... -- |
clears the stack |
Long chains of swap rot over are hard to read. Locals usually do the job better (names).
Inspecting it
. prints the top value as source and say prints it as text, and both pop it. To print the whole stack without changing it:
depth list dup . spread
Limits
The stack holds 1024 values, after which pushing fails with the stack is full. This usually means a loop that pushes without popping. Popping an empty stack fails with drop needs more values on the stack, naming whichever word it was.
The stack is part of the tab's world, and each tab has its own.
