SMoL Translator

This package defines the SMoL language and provides functions that translate SMoL to other languages. The goal is to support translation to at least JavaScript and Python.

Translation to JavaScript is ready. See the SMoL vs JavaScript section for limitations and known incompatibilities between the languages.

Translation to Python is WIP. See the SMoL vs Python section for limitations and known incompatibilities between the languages.

Usage

Most people translate full programs. If this is your case, you can say

import { toJS } from SMoLTranslator;
toJS("program", smolSourceCode)

Replace JS with PY if you want Python-like syntax.

The translator supports more than program-level translation. Shown below is a description of all supported context:

• program: accept any number of terms; every term ends with ; for some languages; top-level expressions are typically wrapped in printing constructs (e.g., console.log(_) for JavaScript and print(_) for Python), except for assignment expressions.
• function-body: accept one or more terms, last of which must be an expression; every term ends with ; for some languages; the last expression is wrapped in return _.
• one-term: accept exactly one term; no ; is added.
• many-terms: accept any number of terms; no ; is added.

Test Suite

This translator has been tested with more than 80% programs from the SMoL Tutor. 154 were tested. 31 were skipped (not tested) for various reasons:

1. (8 skipped) Programs from the heap tutorial. This tutorial is all about heap structure, so expected answers are NOT program outputs.
2. (20 skipped) Programs from the local tutorial. This tutorial is all about local binding forms, which doesn't apply to many languages.
3. (2 skipped) Programs where the expected output involve @. These programs are, again, testing heap structures.
4. (1 skipped) Programs where the expected output involve =. These programs output circular data structures. It is difficult to translate the outputs.

SMoL vs JavaScript

Every SMoL program can be translated to a valid JavaScript program. The translation is straightforward most of the time, except that let expressions (in generally) must be turned into Immediately Invoked Function Expressions.

Program outputs might differ slightly after the translation due to the following language differences:

• In JavaScript, division by zero produces Infinity or a number rather than an error.
• Variable assignment (e.g., x = 2) produces the new value (in this case, 2) rather than a none/void/unit value.
• Indexing an array (known as "vector" in SMoL) outside its index range (e.g., ["a", "b", "c"][99]) produces the undefined value rather than an error.

All 24 test failure (out of 154 tests) are due to the aforementioned reasons.

SMoL vs Python

The translator might produce a Python program that reduces to different results if the source program

• uses set! inside a lambda to assign externally defined variables, or
• expects a distinction between variable definitions and variable assignments, or
• expects variable assignments to produce #<void> (known as None in Python), or
• expects #<void> not be printed, or
• expects infix operators to be valid expressions, or
• expects, for example, (2 + 4) / 2 is 3 rather than 3.0

All 24 test failure (out of 154 tests) are due to the aforementioned reasons.

Key Challenges to the Translation

There are a few key differences between SMoL and the target languages (currently JavaScript and Python):

• return is needed.
• Some SMoL constructs (e.g., if) has an expression version and a statement version in a target language. Even worse, the less flexible target construct (e.g., if statements) is more idiomatic in the target language. So the translator need to use the statement version as often as possible while not doing it blindly.
• Top-level expressions need to be wrapped in a printing construct.
• Python has unusual nonlocal and global keywords