diff options
| -rw-r--r-- | forth.html.markdown | 29 |
1 files changed, 10 insertions, 19 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index aec74333..04804b60 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -10,18 +10,15 @@ Forth was created by Charles H. Moore in the 70s. Note: This article focuses predominantly on the Gforth implementation of Forth, but most of what is written here should work elsewhere. -> If Lisp is the ultimate high level lang, Forth is the ultimate low level lang. - ```forth -\ Forth is an interactive programming language which is comprised of +\ Forth is a low level interactive programming language which is comprised of \ *words*. These are Forth subroutines which are executed once you press \ <Cr>, from left to right. \ --------------------------------- Precursor ---------------------------------- -\ It's important to know how Forth processes instructions. All -\ programming in Forth is done by manipulating what's known as the parameter +\ All programming in Forth is done by manipulating what's known as the parameter \ stack (more commonly just referred to as "the stack"). Typing: 5 2 3 56 76 23 65 @@ -78,9 +75,8 @@ see square \ dup * ; ok \ -------------------------------- Conditionals -------------------------------- -\ In Forth, -1 is used to represent truth, and 0 is used to represent false. -\ The idea is that -1 is 11111111 in binary, whereas 0 is obviously 0 in binary. -\ However, any non-zero value is usually treated as being true: +\ -1 == true, 0 == false. However, any non-zero value is usually treated as +\ being true: 42 42 = \ -1 ok 12 53 = \ 0 ok @@ -123,21 +119,17 @@ threes \ 0 3 6 9 12 ok \ ---------------------------- Variables and Memory ---------------------------- -\ Sometimes we'll be in a situation where we want more permanent variables: -\ First, we use `variable` to declare `age` to be a variable. +\ Use `variable` to declare `age` to be a variable. variable age \ Then we write 21 to age with the word `!`. 21 age ! -\ Finally we can print our variable using the "read" word '@', which adds the +\ Finally we can print our variable using the "read" word `@`, which adds the \ value to the stack, or use `?` 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 @@ -174,8 +166,8 @@ create mynumbers 64 , 9001 , 1337 , \ the last `,` is important! \ ------------------------------ The Return Stack ------------------------------ -\ The return stack is used by Forth to the hold pointers to things when -\ words are executing other words, e.g. loops. +\ The return stack is used 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@`. @@ -190,12 +182,11 @@ create mynumbers 64 , 9001 , 1337 , \ the last `,` is important! \ ------------------------- Floating Point Operations -------------------------- -\ Most Forths tend to dislike the use of floating point operations. We write +\ Most Forths tend to eschew 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: +\ Usually we simply prepend words with 'f' when dealing with floats: variable myfloatingvar \ ok 4.4e myfloatingvar f! \ ok myfloatingvar f@ f. \ 4.4 ok |