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Diffstat (limited to 'forth.html.markdown')
| -rw-r--r-- | forth.html.markdown | 55 |
1 files changed, 51 insertions, 4 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index ee491e7a..06c2c6dc 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -168,17 +168,64 @@ threes \ 0 3 6 9 12 ok \ of `begin` <stuff to do> <flag> `until`. The loop will run until flag is a \ truthy value (not 0). -\ ------------------------------ The Return Stack ------------------------------ +\ ------------------------------ Variables and Memory ------------------------------ -\ TODO +\ Sometimes we'll be in a situation where we want more permanent variables: +\ First, we use `variable` to declare `age` to be a variable. +variable age -\ ------------------------------ Variables and Memory ------------------------------ +\ Then we write 21 to age with the word `!`. +21 age ! + +\ Finally we can print our variable using the "read" word '@', which adds the value +\ to the stack, or use a handy word called `?` that reads and prints it in one go. +age @ . \ 12 ok +age ? \ 12 ok + +\ What's happening here is that `age` stores the memory address, and we use `!` +\ and `@` to manipulate it. + +\ Constants are quite simiar, except we don't bother with memory addresses: +100 constant WATER-BOILING-POINT \ ok +WATER-BOILING-POINT . \ 100 ok + +\ Arrays! + +\ Set up an array of length 3: +variable mynumbers 2 cells allot + +\ Initialize all the values to 0 +mynumbers 3 cells erase +\ (alternatively we could do `0 fill` instead of `erase`, but as we're setting +\ them to 0 we just use `erase`). + +\ or we can just skip all the above and initialize with specific values: + +create mynumbers 64 , 9001 , 1337 , \ the last `,` is important! + +\ ...which is equivalent to: + +\ [64, 9001, 1337] +64 mynumbers 0 cells + ! +9001 mynumbers 1 cells + ! +1337 mynumbers 2 cells + ! + +\ Reading values at certain array indexes: +0 cells mynumbers + ? \ 64 ok +1 cells mynumbers + ? \ 9001 ok +2 cells mynumbers + ? \ 1337 ok + +\ Of course, you'll probably want to define your own words to manipulate arrays: +: ?mynumbers ( n -- n ) cells mynumbers + ; \ ok +64 mynumbers 2 cells + ! \ ok +2 ?mynumbers ? \ 64 ok + +\ ------------------------------ The Return Stack ------------------------------ \ TODO \ ------------------------------ Final Notes ------------------------------ -\ Booleans \ Floats \ Commenting (types) \ bye |