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diff --git a/forth.html.markdown b/forth.html.markdown index 34416878..8cfa46e4 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -7,28 +7,29 @@ filename: learnforth.fs 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. +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 language, Forth is the ultimate low level language. +> 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 *words*. These are -\ Forth subroutines which are executed once you press <Cr>, from left to right. +\ Forth is an 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 stack (more commonly just referred -\ to as "the stack"). Typing: +\ It's important to know how forth processes instructions. 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 \ Makes those numbers get added to the stack, from left to right. .s \ <7> 5 2 3 56 76 23 65 ok -\ Forth's interpreter interprets what you type in one of two ways: as *words* (i.e. the -\ name of subroutines) or as *numbers*. Words are essentially "symbols that do things". +\ Forth's interpreter interprets what you type in one of two ways: as *words* +\ (i.e. the name of subroutines) or as *numbers*. \ ------------------------------ Basic Arithmetic ------------------------------ @@ -47,16 +48,16 @@ of what is written here should work elsewhere. \ And so on. -\ ------------------------------ Stack Manipulation ------------------------------ +\ ----------------------------- Stack Manipulation ----------------------------- -\ Naturally, as we do so much work with the stack, we'll want some useful methods. +\ Naturally, as we work with the stack, we'll want some useful methods: 3 dup - \ duplicate the top item (1st now equals 2nd): 3 - 3 2 5 swap / \ swap the top with the second element: 5 / 2 6 4 5 rot .s \ rotate the top 3 elements: 4 5 6 ok 4 0 drop 2 / \ remove the top item (dont print to screen): 4 / 2 -\ ------------------------------ More Advanced Stack Manipulation ------------------------------ +\ ---------------------- More Advanced Stack Manipulation ---------------------- 1 2 3 4 tuck \ duplicate the top item into the second slot: 1 2 4 3 4 ok 1 2 3 4 over \ duplicate the second item to the top: 1 2 3 4 3 ok @@ -65,7 +66,7 @@ of what is written here should work elsewhere. \ When referring to stack indexes, they are zero-based. -\ ------------------------------ Creating Words ------------------------------ +\ ------------------------------ Creating Words -------------------------------- \ Quite often one will want to write their own words. : square ( n -- n ) dup * ; \ ok @@ -77,7 +78,7 @@ of what is written here should work elsewhere. \ We can check the definition of a word with the `see` word: see square \ dup * ; ok -\ ------------------------------ Conditionals ------------------------------ +\ -------------------------------- 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. @@ -86,22 +87,22 @@ see square \ dup * ; ok 42 42 = / -1 ok 12 53 = / 0 ok -\ `if` is a *compile-only word*. This means that it can only be used when we're compiling a word. -\ when creating conditionals, the format is `if` <stuff to do> `then` <rest of program>. +\ `if` is a *compile-only word*. This means that it can only be used when we're +\ compiling a word. The format is `if` <stuff to do> `then` <rest of program>. : ?>64 ( n -- n ) DUP 64 > if ." Greater than 64!" then ; \ ok 100 ?>64 \ Greater than 64! ok \ Else: -: ?>64 ( n -- n ) DUP 64 > if ." Greater than 64!" else ." Less than 64!" then ; \ ok -100 ?>64 \ Greater than 64! ok -20 ?>64 \ Less than 64! ok +: ?>64 ( n -- n ) DUP 64 > if ." Greater than 64!" else ." Less than 64!" then ; +100 ?>64 \ Greater than 64! ok +20 ?>64 \ Less than 64! ok -\ ------------------------------ Loops ------------------------------ +\ ------------------------------------ Loops ----------------------------------- -\ `do` is like `if` in that it is also a compile-only word, though it uses `loop` as its -\ terminator: +\ `do` is like `if` in that it is also a compile-only word, though it uses +\ `loop` as its terminator: : myloop ( -- ) 5 0 do cr ." Hello!" loop ; \ ok test \ Hello! @@ -110,11 +111,11 @@ test \ Hello! \ Hello! ok -\ `do` expects two numbers on the stack: the end number and the index number, respectively. +\ `do` expects two numbers on the stack: the end number and the index number: \ Get the value of the index as we loop with `i`: -: one-to-15 ( -- ) 15 0 do i . loop ; \ ok -one-to-15 \ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ok +: one-to-12 ( -- ) 12 0 do i . loop ; \ ok +one-to-12 \ 0 1 2 3 4 5 6 7 8 9 10 11 12 ok : squares ( -- ) 10 0 do i DUP * . loop ; \ ok squares \ 0 1 4 9 16 25 36 49 64 81 ok @@ -125,7 +126,7 @@ threes \ 0 3 6 9 12 ok \ Finally, while loops with `begin` <stuff to do> <flag> `unil`: : death ( -- ) begin ." Are we there yet?" 0 until ; -\ ------------------------------ Variables and Memory ------------------------------ +\ ---------------------------- 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. @@ -134,8 +135,8 @@ 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 value -\ to the stack, or use a handy word called `?` that reads and prints it in one go. +\ 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 @@ -180,7 +181,7 @@ create mynumbers 64 , 9001 , 1337 , \ the last `,` is important! \ TODO -\ ------------------------------ Final Notes ------------------------------ +\ --------------------------------- Final Notes -------------------------------- \ Floats \ Commenting (types) |