+
+
+
NovaForth Console
+
+ This is a REPL for NovaForth, using the Vulcan imaginary CPU.
+ You can type lines of Forth code and have them evaluated, and see the results.
+
+
+ For a full introduction to NovaForth, read
+
+ this sample chapter
+
+ from the upcoming Vulcan book. A short tutorial is below:
+
+
Tutorial and examples:
+
+ Forth programs are a series of "words" separated by whitespace. NovaForth evaluates words line-by-line, and a
+ full dictionary of available words is listed below. Here are some example programs:
+
+
+
5 3 + .
+ This program pushes the numbers "5" and "3" to the stack, then adds the top two numbers on the stack, and
+ finally pops the top number from the stack (now "8") and prints it.
+
+
+
." Hello, world!"
+ This program prints a standard greeting.
+
+
+
: square dup * ;
+4 square .
+ This defines a new word, "square", which multiplies the top value on the stack by itself. The second line then
+ calls that word on the number "4" and prints the result.
+
+
+
: collatz
+ dup 2 % if
+ 3 * 1 +
+ else
+ 2 /
+ then ;
+
+4 collatz 5 collatz .s
+ This defines a word "collatz" which showcases conditionals: if the number given to it is odd, it returns triple
+ that number plus one; if it's even, it returns half that number. The ".s" word prints the stack without modifying
+ it and is a useful debugging tool.
+
+
NovaForth Dictionary
+
Arithmetic and stack juggling
+
+ | + | a b -- c | Addition |
+ | - | a b -- c | Subtraction |
+ | * | a b -- c | Multiplication |
+ | / | a b -- c | Division (truncates to integer) |
+ | % | a b -- c | Modulus |
+ | pop | a -- | Throw away the top element of the stack |
+ | dup | a -- a a | Duplicate the top element of the stack |
+ | swap | a b -- b a | Swap the top two elements of the stack |
+
+ | pick |
+ * index -- * el |
+ Copy an element from deep in the stack to the top. "0 pick" is equivalent to dup,
+ "1 pick" pushes the value one below the top, and so on |
+
+ | rot |
+ a b c -- b c a |
+ Rotate the top three elements on the stack |
+
+
+ | -rot |
+ a b c -- c a b |
+ Rotate the top three elements on the stack the other direction (prelude word) |
+
+ | ?dup | a -- a a OR 0 -- 0 | Duplicates the top of stack if it's nonzero |
+ | >r | a -- | Pushes the top of the stack to the R stack |
+ | r> | -- a | Pushes the top of the R stack to the stack |
+ | r@ | -- a | Copies the top of the R stack to the stack, leaving the R stack unchanged |
+ | rpick | index -- a | Picks a value from deep in the R stack, much like "pick" does with the data stack |
+ | rdrop | -- | Drop the top value from the R stack (prelude word) |
+ | lshift | a b -- c | Binary-shifts "a" left "b" bits, shifting in zeroes (prelude word) |
+ | rshift | a b -- c | Binary-shifts "a" right "b" bits, shifting in zeroes (prelude word) |
+ | arshift | a b -- c | Arithmetic right shift: right-shift leaving the high order bit untouched (to preserve sign) (prelude word) |
+ | ror | a -- b | Roll one bit right, moving the low bit to the high bit (prelude word) |
+ | rol | a -- b | Roll one bit left, moving the high bit to the low bit (prelude word) |
+ | over | a b -- a b a | Duplicate the value one below top (prelude word) |
+ | nip | a b -- b | Drop the value one below top (prelude word) |
+ | tuck | a b -- b a b | Duplicate the top value, placing it underneath the one below top (prelude word) |
+ | 2dup | a b -- a b a b | Duplicate the top two values (prelude word) |
+ | negate | a -- b | Multiply the top of stack by -1 (prelude word) |
+ | abs | a -- b | Return the absolute value of the top of stack (prelude word) |
+
+
I/O
+
+ | word word | -- addr | Copies word to the pad, leaving its address on the stack |
+ | pad | -- addr | Pushes the address of the pad to the stack |
+ | number str | -- num 1 OR -- 0 | Tries to parse the given word as a number, pushes the number followed by 1 if it's parseable and 0 if it's not |
+ | hex | -- | Switches all I/O to hexadecimal mode |
+ | dec | -- | Switches all I/O to base-10 mode (the default) |
+ | . | a -- | Prints the number on the top of the stack |
+ | s" | -- addr | Reads a string until a double-quote, copies them to the heap, and returns the address of the string |
+ | ." | -- | Reads a string until a double-quote and prints it |
+ | emit | ch -- | Emits a byte (as ASCII) to the console |
+ | print | addr -- | Prints a null-terminated string to the console |
+ | .s | -- | Prints the stack contents as a debugging aid |
+ | space | -- | Prints a space (prelude word) |
+ | cr | -- | Prints a newline (10 followed by 13, carriage return and line feed) (prelude word) |
+
+
Logic and control structures
+
+ | > | a b -- c | Returns a 1 if a is greater than b, 0 otherwise (signed comparison) |
+ | < | a b -- c | Returns a 1 if a is less than b, 0 otherwise (signed comparison) |
+ | u> | a b -- c | Returns a 1 if a is greater than b, 0 otherwise (unsigned comparison) (prelude word) |
+ | u< | a b -- c | Returns a 1 if a is less than b, 0 otherwise (unsigned comparison) (prelude word) |
+ | = | a b -- c | Returns a 1 if a is equal to b, 0 otherwise |
+ | & | a b -- c | Bitwise-and of a and b |
+ | | | a b -- c | Bitwise-or of a and b |
+ | ^ | a b -- c | Bitwise-xor of a and b |
+ | not | a -- b | If the argument is a 0, returns 1. Otherwise returns 0 |
+ | compare | a b -- c | Compares two strings for equality, returns 1 if they're equal and 0 otherwise |
+ | if / else / then | cond -- | A conditional branch: "condition if truepath else falsepath then". The "else" branch is optional (prelude words) |
+
+
Memory management
+
+ | @ | addr -- val | Read the 3-byte word at the given address |
+ | ! | val addr -- | Write a 3-byte word to the given address |
+ | c@ | addr -- val | Read one byte from the given address |
+ | c! | val addr -- | Write one byte to the given address |
+ | &heap | -- addr | Pushes the address of the heap pointer |
+ | here | -- addr | Pushes the current value of the heap pointer (equivalent to "&heap @") |
+ | variable name | -- | Creates a variable of the given name, which pushes its address when called (prelude word) |
+ | +! | val addr -- | Increments the 3-byte word at "addr" by "val" (prelude word) |
+ | c+! | val addr -- | Increments the byte at "addr" by "val" (prelude word) |
+ | allot | val -- addr | Increment the heap by "val" bytes, returning the start address of the allotted region (prelude word) |
+ | free | val -- addr | Decrement the heap by "val" bytes, returning the new heap address (prelude word) |
+
+
Assembly and compilation
+
+ | execute | addr -- | Calls the given address |
+ | [ | -- | Enters interpret mode |
+ | ] | -- | Enters compile mode |
+ | , | a -- | Compiles a number to the heap |
+ | : | -- | Begins definition of a new word: calls create and enters compile mode |
+ | ; | -- | Ends a word definition: compiles a return instruction and leaves compile mode |
+ | $ mnemonic | -- a | Pushes the equivalent opcode to the given instruction mnemonic |
+ | asm | op -- | Compiles an instruction of the given opcode (with no argument) |
+ | #asm | op arg -- | Compiles an instruction of the given opcode with an argument |
+ | >asm | op -- | Compiles an instruction of the given opcode with a blank argument, and stores the argument's address to the R stack |
+ | resolve | addr -- | Writes the top of the stack to the address on top of the R stack (used to resolve a blank argument left by >asm) |
+ | { | -- | Begins an anonymous function |
+ | } | -- addr | Ends an anonymous function and leaves its address on the stack |
+ | exit | -- | Early return from a word definition |
+ | continue word | -- | Jumps to the given word as a tail call (replacing the current stack frame) |
+ | postpone word | -- | Delays execution of the given word: compiles a call to a compile-mode word or compiles instructions to compile a call to an interpret-mode word (see the NovaForth guide) |
+ | literal | -- addr | Compiles an instruction to push the number at the top of the stack |
+
+
Dictionary manipulation
+
+ | create name | -- | Creates a dictionary entry for a given word (pointing to the heap) |
+ | immediate | -- | Moves the most recently defined word from the interpret dictionary to the compile dictionary |
+ | does> | -- addr | Defines the runtime behavior of a defining word (see the NovaForth guide) |
+ | ' word | -- addr | Consumes a word, looks it up in the dictionary, and returns its address |
+ | ['] | -- addr | Consumes a word at runtime, looks it up in the dictionary, and returns its address |
+
+
Miscellaneous
+
+ | \ | -- | Begins a comment that lasts to the end of the line |
+ | ( | -- | Begins a comment that lasts to the matching close paren |
+
+
Prelude
+
These definitions are run when the console is loaded:
+
+
+
This early-access demo was created by Ross Andrews in January 2023
+
+