Y86_64 FORTH

This is a simple compiler and interpreter for a simple dialect of FORTH. It compiles to Y86_64, specifically for this simulator used in the architecture course at Oxford University. I made this primarily to revise both architecture and compilers simultaneously.

The Language

The language is very simple. You in put a list of symbols (white space separated) they are pushed to the stack in order. You can also push a function (user defined or primitive) which will pop its input of the stack and push the result onto the stack. Functions are defined by starting with a colon, then the function name, the optionally in curly brackets you can pattern match the top of the stack (left is the top). If statements use curly brackets to denote the if and else part.

The grammar is as follows:

Exp  : SExp Exp                    { $1 :> $2 }
     | SExp                        { $1 }

SExp : num                          { Number $1 }
     | id                           { Variable $1 }
     | prim                         { Prim $1 }
     | nop                          { Nop }
     | if '{' Exp '}' '{' Exp '}'   { If $3 $6 }
     | ':' id Exp ';'               { Closure $2 [] $3 }
     | ':'  id '{' List '}' Exp ';' { Closure $2 $4 $6 }

List : id                           { [$1] }
     | id List                      { $1:$2 }

Because learning a language from grammars is not always ideal, here is an example program that finds the 9th Fibonacci number

:dup {a} a a;
:del {a} _;
:swap {a b} a b;

:fib dup 0 == IF {_} {dup 1 == IF {_} {dup 1 - fib swap 2 - fib +}};

9 fib

For a more comprehensive show of the language, see test.f

Using

Building

You will need a modern version of GHC and cabal. Simply run make in the code directory.

The Interpreter

• To use the interpreter (I assume a unix system), simply run ./FORTH -i or ./FORTH --interactive.
• You can give a files as input and it will load in the functions defined in them and prepare the stack.

When the stack grows, the ^ symbol will point to the stop of the stack.

The Compiler

Assuming your code is in the file code.f, run ./FORTH -o OutFile code.f. If you do not specify an output, the code will be printed to stdout. You can turn off optimisation with -n or --no-opt although it will still do some inlining.

To run the code, copy it into this simulator and hit run. The stop of the stack at the end of the simulation is denoted by < RSP and the bottom is at 0x01f8

To test the compiler, run ./FORTH test.f

Quirks

1. The order you give the files to the compiler (for now) matters if you don't use #include file directives. If file A relies on functions in file B, write ./FORTH B A
2. The base pointer and stack pointer share a small stack in the simulator. The base pointer is used to save the call stack. You you find that this makes the stack too small, you can change the initial base pointer address with -b <address> or --base-pointer <number>