From a76977af62010a392c16010c367185e61e856ffe Mon Sep 17 00:00:00 2001 From: Dimitri Sokolyuk Date: Wed, 30 Oct 2019 20:04:56 +0100 Subject: mv to docs --- doc/learnforth.fs | 205 ------------------------------------------------------ 1 file changed, 205 deletions(-) delete mode 100644 doc/learnforth.fs (limited to 'doc/learnforth.fs') diff --git a/doc/learnforth.fs b/doc/learnforth.fs deleted file mode 100644 index 2f8efe7..0000000 --- a/doc/learnforth.fs +++ /dev/null @@ -1,205 +0,0 @@ - -\ 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 the parameter stack (more -\ commonly just referred to as "the stack"). -5 2 3 56 76 23 65 \ ok - -\ Those numbers get added to the stack, from left to right. -.s \ <7> 5 2 3 56 76 23 65 ok - -\ In Forth, everything is either a word or a number. - -\ ------------------------------ Basic Arithmetic ------------------------------ - -\ Arithmetic (in fact most words requiring data) works by manipulating data on -\ the stack. -5 4 + \ ok - -\ `.` pops the top result from the stack: -. \ 9 ok - -\ 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 ----------------------------- - -\ 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 -4 0 drop 2 / \ remove the top item (don't print to screen): 4 / 2 -1 2 3 nip .s \ remove the second item (similar to drop): 1 3 - -\ ---------------------- More Advanced Stack Manipulation ---------------------- - -1 2 3 4 tuck \ duplicate the top item below 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 -1 2 3 4 2 roll \ *move* the item at that position to the top: 1 3 4 2 ok -1 2 3 4 2 pick \ *duplicate* the item at that position to the top: 1 2 3 4 2 ok - -\ When referring to stack indexes, they are zero-based. - -\ ------------------------------ Creating Words -------------------------------- - -\ The `:` word sets Forth into compile mode until it sees the `;` word. -: square ( n -- n ) dup * ; \ ok -5 square . \ 25 ok - -\ We can view what a word does too: -see square \ : square dup * ; ok - -\ -------------------------------- Conditionals -------------------------------- - -\ -1 == true, 0 == false. However, any non-zero value is usually treated as -\ being true: -42 42 = \ -1 ok -12 53 = \ 0 ok - -\ `if` is a compile-only word. `if` `then` . -: ?>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 ; -100 ?>64 \ Greater than 64! ok -20 ?>64 \ Less than 64! ok - -\ ------------------------------------ Loops ----------------------------------- - -\ `do` is also a compile-only word. -: myloop ( -- ) 5 0 do cr ." Hello!" loop ; \ ok -myloop -\ Hello! -\ Hello! -\ Hello! -\ Hello! -\ Hello! ok - -\ `do` expects two numbers on the stack: the end number and the start number. - -\ 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 - -\ `?do` works similarly, except it will skip the loop if the end and start -\ numbers are equal. -: squares ( n -- ) 0 ?do i square . loop ; \ ok -10 squares \ 0 1 4 9 16 25 36 49 64 81 ok - -\ Change the "step" with `+loop`: -: threes ( n n -- ) ?do i . 3 +loop ; \ ok -15 0 threes \ 0 3 6 9 12 ok - -\ Indefinite loops with `begin` `until`: -: death ( -- ) begin ." Are we there yet?" 0 until ; \ ok - -\ ---------------------------- Variables and Memory ---------------------------- - -\ Use `variable` to declare `age` to be a variable. -variable age \ ok - -\ Then we write 21 to age with the word `!`. -21 age ! \ ok - -\ 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 @ . \ 21 ok -age ? \ 21 ok - -\ Constants are quite similar, except we don't bother with memory addresses: -100 constant WATER-BOILING-POINT \ ok -WATER-BOILING-POINT . \ 100 ok - -\ ----------------------------------- Arrays ----------------------------------- - -\ Creating arrays is similar to variables, except we need to allocate more -\ memory to them. - -\ You can use `2 cells allot` to create an array that's 3 cells long: -variable mynumbers 2 cells allot \ ok - -\ Initialize all the values to 0 -mynumbers 3 cells erase \ ok - -\ 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!) - -\ ...which is equivalent to: - -\ Manually writing values to each index: -64 mynumbers 0 cells + ! \ ok -9001 mynumbers 1 cells + ! \ ok -1337 mynumbers 2 cells + ! \ ok - -\ Reading values at certain array indexes: -0 cells mynumbers + ? \ 64 ok -1 cells mynumbers + ? \ 9001 ok - -\ We can simplify it a little by making a helper word for manipulating arrays: -: of-arr ( n n -- n ) cells + ; \ ok -mynumbers 2 of-arr ? \ 1337 ok - -\ Which we can use for writing too: -20 mynumbers 1 of-arr ! \ ok -mynumbers 1 of-arr ? \ 20 ok - -\ ------------------------------ The Return Stack ------------------------------ - -\ 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@`. -: myloop ( -- ) 5 0 do r@ . loop ; \ ok - -\ 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, `>r` should -\ always be followed by `r>`. - -\ ------------------------- Floating Point Operations -------------------------- - -\ 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: -variable myfloatingvar \ ok -4.4e myfloatingvar f! \ ok -myfloatingvar f@ f. \ 4.4 ok - -\ --------------------------------- Final Notes -------------------------------- - -\ Typing a non-existent word will empty the stack. However, there's also a word -\ specifically for that: -clearstack - -\ Clear the screen: -page - -\ Loading Forth files: -\ s" forthfile.fs" included - -\ You can list every word that's in Forth's dictionary (but it's a huge list!): -\ words - -\ Exiting Gforth: -\ bye - - -- cgit v1.2.3