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| -rw-r--r-- | forth.html.markdown | 31 |
1 files changed, 11 insertions, 20 deletions
diff --git a/forth.html.markdown b/forth.html.markdown index c61633c2..34416878 100644 --- a/forth.html.markdown +++ b/forth.html.markdown @@ -21,31 +21,26 @@ of what is written here should work elsewhere. \ 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"). The stack is a typical last-in-first-out (LIFO) stack. Typing: +\ to as "the stack"). Typing: 5 2 3 56 76 23 65 -\ Means 5 gets put on the stack first, then 2, then 3, etc all the way to 65, which -\ is now at the top of the stack. We can see the length and contents of the stack by -\ passing forth the word `.s`: -.s <7> 5 2 3 56 76 23 65 \ ok +\ 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". -\ Finally, as the stack is LIFO, we obviously must use postfix notation to manipulate -\ the stack. This should become clear shortly. - \ ------------------------------ Basic Arithmetic ------------------------------ -\ Lets do a simple equation: adding 5 and 4. In infix notation this would be 5 + 4, -\ but as forth works in postfix (see above about stack manipulation) we input it like so: +\ Arithmetic (in fact most words requiring data) works by manipulating data on +\ the stack. 5 4 + \ ok -\ However, this alone yields "ok", yet no answer. Typing the word `.` will yield -\ the result. +\ 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 `.`: . \ 9 ok -\ This should illustrate how Forth's stack works. Lets do a few more arithmetic tests: +\ A few more examples of arithmetic 6 7 * . \ 42 ok 1360 23 - . \ 1337 ok 12 12 / . \ 1 ok @@ -75,19 +70,15 @@ of what is written here should work elsewhere. \ Quite often one will want to write their own words. : square ( n -- n ) dup * ; \ ok -\ Lets break this down. The `:` word says to Forth to enter "compile" mode. After that, -\ we tell Forth what our word is called - "square". Between the parentheses we have a -\ comment depicting what this word does to the stack - it takes a number and adds a -\ number. Finally, we have what the word does, until we reach the `;` word which -\ says that you've finished your definition, Forth will add this to the dictionary and -\ switch back into interpret mode. +\ 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. \ We can check the definition of a word with the `see` word: see square \ dup * ; ok \ ------------------------------ Conditionals ------------------------------ -\ Booleans: \ 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: |