diff options
| author | Matthew D. Scholefield <matthew331199@gmail.com> | 2023-12-14 06:56:16 -0800 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2023-12-14 15:56:16 +0100 |
| commit | be771f6c2eacdc247ec32bd153cb7e23a689fee1 (patch) | |
| tree | db2c00875685874ba67e58ac8b18205873c03035 | |
| parent | 79538b5bcb593cb2f6be4b03f78cc94de9e2e49b (diff) | |
[forth/en] Clarify bounds of do and the difference between ?do vs do (#4058)
* Clarify bounds of do and ?do vs do
* Re-introduce square into example
---------
Co-authored-by: ven <vendethiel@hotmail.fr>
| -rw-r--r-- | forth.html.markdown | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index ab0c4c3b..4e2f7599 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -93,8 +93,8 @@ see square \ : square dup * ; ok \ ------------------------------------ Loops ----------------------------------- -\ `do` is also a compile-only word. -: myloop ( -- ) 5 0 do cr ." Hello!" loop ; \ ok +\ `?do` is also a compile-only word. +: myloop ( -- ) 5 0 ?do cr ." Hello!" loop ; \ ok myloop \ Hello! \ Hello! @@ -102,16 +102,17 @@ myloop \ Hello! \ Hello! ok -\ `do` expects two numbers on the stack: the end number and the start number. +\ `?do` expects two numbers on the stack: the end number (exclusive) and the +\ start number (inclusive). \ We can get the value of the index as we loop with `i`: : one-to-12 ( -- ) 12 0 do i . loop ; \ ok one-to-12 \ 0 1 2 3 4 5 6 7 8 9 10 11 ok -\ `?do` works similarly, except it will skip the loop if the end and start -\ numbers are equal. -: squares ( n -- ) 0 ?do i square . loop ; \ ok -10 squares \ 0 1 4 9 16 25 36 49 64 81 ok +\ `do` works similarly, except if start and end are exactly the same it will +\ loop forever (until arithmetic underflow). +: loop-forever 1 1 do i square . loop ; \ ok +loop-forever \ 1 4 9 16 25 36 49 64 81 100 ... \ Change the "step" with `+loop`: : threes ( n n -- ) ?do i . 3 +loop ; \ ok |