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| -rw-r--r-- | forth.html.markdown | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index bea7cf38..ee491e7a 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -110,12 +110,12 @@ see square \ dup * ; ok \ Booleans: \ In forth, -1 is used to represent truth, and 0 is used to represent false. \ The idea behind this 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. +\ 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. This means that it can *only* be used when we're compiling a word. +\ `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 <boolean> `if` <stuff to do> `then` <rest of program>. : ?>64 ( n -- n ) DUP 64 > if ." Greater than 64!" then ; \ ok @@ -132,7 +132,41 @@ see square \ dup * ; ok \ ------------------------------ Loops ------------------------------ -\ TODO +\ `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! +\ Hello! +\ Hello! +\ Hello! +\ Hello! ok + +\ `do` expects two numbers before it: the end number and the index number, respectively. +\ (cr means carraige-return, essentially it a newline). This is equivalent to a for-loop +\ in other languages, with a definite number of times to loop. + +\ So what if we want to get the value of the index as we loop? We use `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 +: squares ( -- ) 10 0 do i DUP * . loop ; \ ok +squares \ 0 1 4 9 16 25 36 49 64 81 ok + +\ Thidly, we can also change how large the step is between each loop iteration with `+loop`. +\ `+loop` reads the number on the top of the stack for how far to move each iteration. + +: threes ( -- ) 15 0 do i . 3 +loop ; \ ok +threes \ 0 3 6 9 12 ok + +\ Finally, while loops: + +: death ( -- ) begin ." Are we there yet?" 0 until ; + +\ Will print "Are we there yet?" forever. While loops are constructed in the format +\ of `begin` <stuff to do> <flag> `until`. The loop will run until flag is a +\ truthy value (not 0). \ ------------------------------ The Return Stack ------------------------------ |