iskm/learnxinyminutes-docs
1
0
Fork 0
mirror of https://github.com/adambard/learnxinyminutes-docs.git synced 2024-12-23 09:41:36 +00:00
Code Issues Actions Packages Projects Releases Wiki Activity

Slim down comments.

Browse Source
This commit is contained in:
HorseMD 2014-11-13 23:25:48 +00:00
parent edba1b39c8
commit e001c352ca
1 changed files with 10 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
forth.html.markdown
View File

@ -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