Gabelang

Overview

This is a language I am writing in rust for fun and to learn more about lexers, parsers, interpreters, and to dymistify programming languages in general. The Writing an Interpreter in Go book by Thorsten Ball was used as a reference and insperation for this project as well as mkdb by Antonio Sarosi.

BNF / Language Grammer

<program> = <statement> | <program> <statement>
<statement> = <let_statement> | <if_statement> | <while_loop> | <func_decl> | <expression>
<let_statement> = let <identifier> = <expression>;
<assign_statement> = <assignable> = <expression>;
<if_statement> = if <expression> <code_block>
<while_loop> = while <expression> <code_block>
<for_loop> = for(<statement> <expression>; <statement>) <code_block>
<func_decl> = fn <identifier> <param_idents> <codeblock>
<code_block> = {<program>}
<param_idents> = (<_param_idents>)
<_param_idents> = <identifier> | <_param_idents>, <_param_idents>
<identifier> = <ident_char> | <ident_char><identifier>
<indent_char> = <ALPHACHAR> | _
<expression> = <group_expression> | <operation_expression> | <assignable> | <func_call> | <object_literal> | <array_literal>  | <number_literal>
<group_expression> = (<expression>)
<operation_expression> = <expression> <op> <expression>
<op> = + | - | * | /
<assignable> = <identifier> | <array_index> | <object_prop>
<array_index> = <assignable>[<expression>]
<object_prop> = <assignable>.<identifier>
<func_call> = <assignable>(<expression_list>)
<object_literal> = {<object_field_literals>}
<object_field_literals> = <identifier>: <expression> | <object_field_literals>, <object_field_literals>
<array_literal> = [<expression_list>]
<expression_list> = <expression> | <expression_list>, <expression_list>
<number_literal> = <number> | <number><number_literal>
<number> = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0

Commenting

Comment your code using the //comment syntax Any text to the right of a double slash does not make it to the parser or interpretter and will not be evaluated as code

// This function doubles a number
fn double_num(num) {
    // Multiplies num by 2 to get the answer
    return num * 2;
}

Variable Behavior

• When a variable is used as an expression/rvalue it is deep cloned

Built in Functions

len(obj) -> number

• returns the length of an array or string
• returns the number of keys in an object
• throws an error if provided with something other than an array, object, or string

reverse(obj) -> array | string

• returns a new reversed array or string without changing the parameter object
• throws an error if provided with something other than an array or string

abs(number) -> number

• returns the absolute value of a passed in number
• throws an error if provided with something other than a number

open(path) -> string

• returns the contents of the file at path as a string
• throws an error if file reading fails
• throws an error if provided with something other than a string

print(any) -> null

• prints a value to stdout followed by a newline
• accepts any value (numbers, strings, arrays, objects, booleans, null, functions)

prompt(string) -> string

• prints the prompt message to stdout (no trailing newline), reads a line from stdin, and returns it with the trailing newline stripped
• throws an error if the argument is not a string or if reading stdin fails

char_code(string, index) -> number

• returns the byte value (0-255) at the given index of the string
• throws an error if the first argument is not a string or the second is not a number
• throws an error if the index is negative or out of bounds

substring(string, start, end) -> string

• returns the substring from start (inclusive) to end (exclusive)
• throws an error if string is not a string or start/end are not numbers
• throws an error if start < 0, end < 0, start > end, or end exceeds the string length

concat(a, b) -> string

• returns the string formed by concatenating the string representations of a and b
• accepts any combination of value types; both are stringified before joining

Build

Build with

cargo build --release

Build for wasm target

Requires wasm-pack to be installed

cargo install wasm-pack

Build with

wasm-pack build --features wasm

Install

Requires cargo to be installed

Install gabelang with

cargo install gabelang

Run

Run as repl with

gabelang

or run a script with

gabelang [script name]
gabelang --file [script name]

Test

Run tests with

cargo test

Todo

• Better Documentation
• Built in Functions(print, file, fetch, input)
• Add tests to ast and eval modules
• Add fun language syntax
• Improve garbage collector to use mark and sweep

Todo Reach

• Add tooling/language server
• Add bytecode compiler
• Create VM that can run bytecode