https://github.com/arsalan0c/non-deterministic-source
Metacircular evaluator for a non-deterministic language (based on SICP JS: https://sicp.comp.nus.edu.sg/chapters/85)
https://github.com/arsalan0c/non-deterministic-source
amb evaluator metacircular-interpreter non-deterministic sicp-js
Last synced: 4 months ago
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Metacircular evaluator for a non-deterministic language (based on SICP JS: https://sicp.comp.nus.edu.sg/chapters/85)
- Host: GitHub
- URL: https://github.com/arsalan0c/non-deterministic-source
- Owner: arsalan0c
- Created: 2020-05-05T15:13:01.000Z (about 5 years ago)
- Default Branch: master
- Last Pushed: 2021-02-07T14:59:54.000Z (over 4 years ago)
- Last Synced: 2025-02-06T04:12:54.846Z (5 months ago)
- Topics: amb, evaluator, metacircular-interpreter, non-deterministic, sicp-js
- Language: JavaScript
- Homepage:
- Size: 78.1 KB
- Stars: 1
- Watchers: 0
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
# non-deterministic-source
Metacircular evaluator for the non-deterministic [Source](https://sicp.comp.nus.edu.sg/source/) 4.3 programming language with John McCarthy's `amb` operator for ambiguous choice.
Implementation is in: [evaluator.js](evaluator.js)
## Run using `parse_and_eval`
Example:
Find integers between 0 and 12 (inclusive) that are divisible by 2 or 3.
```js
parse_and_eval("function int_between(low, high) {\
return low > high ? amb() : amb(low, int_between(low + 1, high));\
}\
function is_even(x) { return (x % 2) === 0;}\
function divisible_by_three(x) { return (x % 3) === 0;}\
let integer = int_between(0, 12);\
require(is_even(integer) || divisible_by_three(integer));\
integer;");
// result: 0
```
Subsequent values can be generated by typing:
```js
try_again(); // result: 2
try_again(); // result: 3
try_again(); // result: 4
try_again(); // result: 6
try_again(); // result: 8
try_again(); // result: 9
try_again(); // result: 10
try_again(); // result: 12
try_again(); // result: null
```
### Other quick examples
```js
/* SAT solving */
parse_and_eval("\
let P = amb(true, false); \
let Q = amb(true, false); \
let R = amb(true, false); \
let S = amb(true, false); \
\
let formula = (P || !Q || R) && (!P || Q || S) && (Q || !S) && (R || S) && (P || !R); \
require(formula === true); \
\
display('Satisfying Assignment:');\
display(P, 'P:'); \
display(Q, 'Q:'); \
display(R, 'R:'); \
display(S, 'S:'); \
");
// use `try_again()` to view all satisfying assignments.
```
```js
parse_and_eval("const integer_from = n => amb(n, integer_from(n + 1)); integer_from(1);");
// result: 1
try_again(); // result: 2
try_again(); // result: 3
try_again(); // result: 4 ... and so on...
```
```js
parse_and_eval("const f = amb(1, 2, 3); const g = amb(5, 6, 7); f;");
// Result: 1, 1, 1, 2, 2, 2, 3, 3, 3 (use the try_again() function)
```
```js
parse_and_eval("const f = amb(1, 2, 3); const g = amb(5, 6, 7); g;");
// Result: 5, 6, 7, 5, 6, 7, 5, 6, 7 (use the try_again() function)
```
## Running Tests
1. Copy the code from the following files into the [playground](https://sourceacademy.nus.edu.sg/playground):
* `evaluator.js`
* `test.js`
* `source-test/main.js`
2. Remove one of the two instances of the repeated function `variable_declaration_name` (from `evaluator.js` and `source-test/main.js`)
## Changes from SICP JS
This implementation of the evaluator contains several changes from that shown in the textbook. These consist of enhancements as well as bug fixes.
In descending order of complexity:
* Added logic to correctly evaluate return statements.
[#3](https://github.com/anubh-v/non-deterministic-source/pull/3), [#26](https://github.com/anubh-v/non-deterministic-source/pull/26)
* Added tests for deterministic and non-deterministic functionality. [#8](https://github.com/anubh-v/non-deterministic-source/pull/8)
* Fixed `execute_application` to ensure that when a function is applied, the extended environment includes
names declared in the function body.
* Solved SICP JS exercise 4.45 by implementing `analyze_require`.
* Provided a more convenient method of running programs.
The textbook implementation accepts programs via a continuously running prompt.
In our implementation, users can instead use the `parse_and_eval` and `try_again` functions to run programs. This allows longer programs to be written easily. [#6](https://github.com/anubh-v/non-deterministic-source/pull/6), [#16](https://github.com/anubh-v/non-deterministic-source/pull/16)
* Added support for logical operators `&&` and `||`. [#9](https://github.com/anubh-v/non-deterministic-source/pull/9)
* Added the unary minus operator. [#22](https://github.com/anubh-v/non-deterministic-source/pull/22)
* Prevented re-assignment to constants. [#13](https://github.com/anubh-v/non-deterministic-source/pull/13)
* Added support for lists via the `list` function. [#5](https://github.com/anubh-v/non-deterministic-source/pull/5)
* Improved documentation of some functions. [#11](https://github.com/anubh-v/non-deterministic-source/pull/11)
## Acknowledgements
This metacircular evaluator is built based on [SICP JS, Chapter 4.3](https://sicp.comp.nus.edu.sg/chapters/85).
We used a metacircular evaluator for Source 1, provided in CS4215 materials, as a starting point for this evaluator.
It also uses the `parse` function of the [Source Academy](https://github.com/source-academy/js-slang)