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diff --git a/forth.html.markdown b/forth.html.markdown index a6b17a5d..46b912b4 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -13,21 +13,19 @@ Note: This article focuses predominantly on the Gforth implementation of Forth, but most of what is written here should work elsewhere. ```forth -\ 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. +\ This is a comment +( This is also a comment but it's only used when defining words ) \ --------------------------------- Precursor ---------------------------------- -\ All programming in Forth is done by manipulating what's known as the parameter -\ stack (more commonly just referred to as "the stack"). Typing: +\ All programming in Forth is done by manipulating the parameter stack (more +\ commonly just referred to as "the stack"). 5 2 3 56 76 23 65 \ ok -\ Makes those numbers get added to the stack, from left to right. +\ 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*. +\ In Forth, everything is either a word or a number. \ ------------------------------ Basic Arithmetic ------------------------------ @@ -35,14 +33,19 @@ Forth, but most of what is written here should work elsewhere. \ the stack. 5 4 + \ ok -\ This adds 5 and 4 to the stack and then `+` is called, which removes them and -\ adds the result to the stack. We can see it with `.`: +\ `.` pops the top result from the stack: . \ 9 ok -\ A few more examples of arithmetic +\ More examples of arithmetic: 6 7 * . \ 42 ok 1360 23 - . \ 1337 ok 12 12 / . \ 1 ok +13 2 mod . \ 1 ok + +99 negate . \ -99 ok +-99 abs . \ 99 ok +52 23 max . \ 52 ok +52 23 min . \ 23 ok \ ----------------------------- Stack Manipulation ----------------------------- @@ -67,11 +70,8 @@ Forth, but most of what is written here should work elsewhere. \ Quite often one will want to write their own words. : square ( n -- n ) dup * ; \ ok -\ The `:` word sets Forth into compile mode. `(` and `)` are both words which -\ tell Forth to ignore between them. Up until the `;` word is what our word -\ does. +\ The `:` word sets Forth into compile mode until it sees the `;` word. -\ We can check the definition of a word with the `see` word: see square \ dup * ; ok \ -------------------------------- Conditionals -------------------------------- @@ -81,8 +81,7 @@ 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. The format is `if` <stuff to do> `then` <rest of program>. +\ `if` is a compile-only word. `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 @@ -93,8 +92,7 @@ see square \ dup * ; ok \ ------------------------------------ Loops ----------------------------------- -\ `do` is like `if` in that it is also a compile-only word, though it uses -\ `loop` as its terminator: +\ `do` is also a compile-only word. : myloop ( -- ) 5 0 do cr ." Hello!" loop ; \ ok myloop \ Hello! @@ -108,12 +106,12 @@ myloop \ We can get the value of the index as we loop with `i`: : 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 ( -- ) 0 do i dup * . loop ; \ ok +: squares ( n -- ) 0 do i dup * . loop ; \ ok 10 squares \ 0 1 4 9 16 25 36 49 64 81 ok \ Change the "step" with `+loop`: -: threes ( -- ) do i . 3 +loop ; \ ok -15 0 threes \ 0 3 6 9 12 ok +: threes ( n n -- ) do i . 3 +loop ; \ ok +15 0 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 ; \ ok @@ -142,8 +140,9 @@ variable mynumbers 2 cells allot \ ok \ Initialize all the values to 0 mynumbers 3 cells erase \ ok -\ (alternatively we could do `0 fill` instead of `erase`, but as we're setting -\ them to 0 we just use `erase`). + +\ Alternatively we could use `fill`: +mynumbers 3 cells 0 fill \ or we can just skip all the above and initialize with specific values: create mynumbers 64 , 9001 , 1337 , \ ok (the last `,` is important!) @@ -177,14 +176,12 @@ create mynumbers 64 , 9001 , 1337 , \ ok (the last `,` is important!) \ 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 ok -\ 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>`. +\ NOTE: Because Forth uses the return stack for word pointers, `>r` should +\ always be followed by `r>`. \ ------------------------- Floating Point Operations -------------------------- -\ Most Forths tend to eschew the use of floating point operations. We write -\ floating point operations with scientific notation. +\ Most Forths tend to eschew the use of floating point operations. 8.3e 0.8e f+ f. \ 9.1 ok \ Usually we simply prepend words with 'f' when dealing with floats: |