albert

Albert is an interpreter for the Monkey programming language and written in Rust. The source code is based on the code described in the following two books:

• Writing an Interpreter in Go
• Writing a Compiler in Go

The original source code was written in Go.

usage

There are two backends implemented. The first one, is a classic tree-walking interpreter that can be invoked by using the command:

repl -b tw path/to/scriptfile

The second backend is a bytecode compiler that can be invoked by using the command:

repl -b vm path/to/scriptfile

If a script file is not given, both of these commands will load the REPL.

There is actually a third backend implemented, vmd that dumps the bytecode of a given script. For example, consider the following script:

let fib = fn(n) {
    if (n < 2) { 
        n 
    } else {
        fib(n-1) + fib(n-2)
    }
};
fib(33);

Assuming the above script is in a file named fib.mnk, we can dump bytecode information by invoking the command:

repl -b vmd fib.mnk

and get the following output:

[CONSTANTS]
0000: 2
0001: 1
0002: 2
0003: function(0)
0004: 33
[STRINGS]
[INSTRUCTIONS]
[   0] CLOSURE 3 0 
[   4] SET_GLOBAL 0 
[   7] GET_GLOBAL 0 
[  10] CONSTANT 4 
[  13] CALL 1 
[  15] POP 
[FUNCTIONS]
#0000
[   0] GET_LOCAL 0 
[   2] CONSTANT 0 
[   5] LESS_THAN 
[   6] JUMP_IF_FALSE 14 
[   9] GET_LOCAL 0 
[  11] JUMP 33 
[  14] CURRENT_CLOSURE 
[  15] GET_LOCAL 0 
[  17] CONSTANT 1 
[  20] SUB 
[  21] CALL 1 
[  23] CURRENT_CLOSURE 
[  24] GET_LOCAL 0 
[  26] CONSTANT 2 
[  29] SUB 
[  30] CALL 1 
[  32] ADD 
[  33] RETVAL

features

Not all features of the original Monkey language are implemented. Those implemented for the two supported backends are shown in the following table:

feature	tw	vm
Numbers	✔️	✔️
Strings	✔️	✔️
Arrays	✔️	✔️
Functions	✔️	✔️
Closures	✔️	✔️
Hash Tables	✖️	✖️
Builtins	✖️	✖️
Power ^ op	✔️	✔️
Macros	✖️	✖️

features scheduled for future versions

feature	version	status
Better error messages	v0.2	master
Faster execution (tw)	v0.2	master
double-precision numbers instead of integers	v0.2	master
print builtin	v0.2
assert builtin	v0.2
support while loops	v0.2
macros	v0.3
a module system	v0.4