lox.rs

Rust implementation for the Lox language (from Crafting Interpreters).

Supported Features

• Data Types: boolean, number, string, nil
• Expressions: binary, unary, comparision
• Statements: if, print, return, while
• Declarations: functions (with closures), variables
• Native Functions (FFI): clock, read_stdin

Missing Features

• Classes (with inheritance)

Execution

There are currently three possibilities:

o Interpreter Mode o REPL Mode o AST Mode

Interpreter Mode

The Interpreter mode runs a complete script file and prints the output on stdout. For example, assuming the follwing code in script.lox:

var i = 1;
print i;

Execute the code with:

lox run script.lox

REPL Mode

The REPL mode (read-eval-print loop) instantly executes individual statements entered on the command-line. The REPL mode is started with:

lox repl

This opens up a CLI prompt:

lox> var i = 1;
lox> fun some_func (p) { print p; }
lox> some_func(i);
1
lox>

AST Mode

The AST mode prints the Abstract Syntax Tree of an input program. Assuming again the above script.lox, the AST gets printed on the command-line by:

lox print-ast script.lox

The output is:

Abstract Syntax Tree
====================
(list
    (var-decl
        i
        (number 1)
    )
    (print
        (var i)
    )
)
====================

This command additionally supports printing location information, i.e. the location where some entity (e.g. variable) was defined:

lox print-ast --show-location script.lox

This then outputs the location information in brackets:

Abstract Syntax Tree
====================
(list [1:1-2:8]
    (var-decl [1:1-1:10]
        i
        (number 1) [1:9-1:9]
    )
    (print [2:1-2:8]
        (var i) [2:7-2:7]
    )
)
====================