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| -rw-r--r-- | forth.html.markdown | 30 |
1 files changed, 26 insertions, 4 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index 11300159..2c2c480e 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -18,7 +18,7 @@ Forth, but most of what is written here should work elsewhere. \ *words*. These are Forth subroutines which are executed once you press \ <Cr>, from left to right. -\ ------------------------------ Precursor ------------------------------ +\ --------------------------------- Precursor --------------------------------- \ It's important to know how forth processes instructions. All \ programming in Forth is done by manipulating what's known as the parameter @@ -174,12 +174,34 @@ create mynumbers 64 , 9001 , 1337 , \ the last `,` is important! \ ------------------------------ The Return Stack ------------------------------ -\ TODO +\ The return stack is used by Forth to the hold pointers to things when +\ words are executing other words, e.g. loops. + +\ We've already seen one use of it: `i`, which duplicates the top of the return +\ stack. `i` is equivalent to `r@`. +: myloop ( -- ) 5 0 do r@ . loop ; + +\ As well as reading, we can add to the return stack and remove from it: +5 6 4 >r swap r> .s \ 6 5 4 + +\ NOTE: Because forth uses the return stack for word pointers, it's essential +\ that you set the return stack back to how it was at the end of your +\ definition. `>r` should always be followed by `r>`. + +\ ------------------------- Floating Point Operations ------------------------- + +\ Most forths tend to dislike the use of floating point operations. We write +\ floating point operations with scientific notation. +8.3e 0.8e f+ f. \ 9.1 ok + +\ Usually we can just prepend arithmetic words with 'f' to use floating point +\ arithmetic: +variable myfloatingvar +4.4e myfloatingvar f! +myfloatingvar f@ f. \ --------------------------------- Final Notes -------------------------------- -\ Floats -\ Commenting (types) \ bye ``` |