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A hands-on, test driven guide to implementing a simple programming language

License: BSD 3-Clause "New" or "Revised" License

Python 97.34% Shell 1.70% Batchfile 0.96%

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Question about scopes / environments

First, I want to thank you for this amazing project. Right now, I am working on part 8 and I can tell you that I have learnt and enjoyed the process a lot.

I am not sure if this is the right place to ask for help (I could't find any information about where help question should be asked).

Anyway, I am looking for guidance on how should I approach this situation:

def test_let_bindings_overshadow_outer_environment():
    """
    Let bindings should shadow definitions in from outer environments
    """

    interpret("(define foo 1)", env)

    program = """
        (let ((foo 2))
             foo)
    """

My evaluator function creates a new Environment every time it found a "let" special form, which is created by extending the one its belong to:

def eval_let(ast, env):
    let_env = env.extend({})

    bindings = ast[1]

    print bindings

    args = {}
    for b in bindings:
        key = b[0]
        val = evaluate(b[1], let_env)
        args[key] = val
        let_env.set(key, val)

    print args

    return evaluate(ast[2], let_env)

However, this only work if I allow override already defined variables in my Environment (this way I can use the set method to change the value of a variable), but this doesn't seem to be right way to do it because I can also define multiple times the same variable, which of course is wrong.

How should I implement this behaviour correctly?. I need to be able to read variables from the parent environment and at the same time, define a local variable without raising a duplicated definition error.

Thanks!!

Parser tests don't cover ints

In yesterday's workshop my parser implementation passed the first test series although I cast digit strings to float. It made later tests fail with no apparent reason.

So the parser tests should check that numbers are ints.

Btw thanks for this very interesting workshop! Enjoyed it yesterday!

Why is eq working only on atoms?

https://github.com/kvalle/diy-lisp/blob/master/tests/test_2_evaluating_simple_expressions.py#L61

I assume that '(1 2 3) isn't the same as '(1 2 3) because it's not an atom, but why such a restriction?

Missing license

Hi,

Great project! Would it be possible for you to add a license to it (hopefully a permissive one)?

I'm in the process of doing the "tutorial" in NodeJS and I'm porting the tests almost verbatim to JS. When I'm finished I was hoping to create a clone of your project in NodeJS.

repl broken in Python 2

repl doesn't work in Python 2 because input is evaluated as python code immediately (which results in a Python exception). The reason seems to be the port to Python 3 that was done a few weeks ago.

repl.ly:68: line = input(colored(prompt, "grey", "bold"))

Possible workaround could be to use raw_input in Python 2 and input in Python 3 (Add in reply.py somewhere):

try:
   input = raw_input
except NameError:
   pass

Solution tests fails

$ ./run-tests.sh
................................F
======================================================================
FAIL: TEST 2.6: To be able to do anything useful, we need some basic math
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/nix/store/8z65fg9wa4vxi8sa4v55yyx00yj2wcrb-python3.6-nose-1.3.7/lib/python3.6/site-packages/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/home/simendsjo/bekk/fagdag-feb-2019/diy-lang/tests/test_2_evaluating_simple_expressions.py", line 87, in test_basic_math_operators
    assert_equals(3, evaluate(["/", 7, 2], Environment()))
AssertionError: 3 != 3.5

----------------------------------------------------------------------
Ran 33 tests in 0.004s

FAILED (failures=1)

The ' (quote) symbol is not well defined

I went through the tutorial and it is great!

However, I think the handling of the quote symbol can be better explained. 'quote' is defined as follows in part 2:

quote takes one argument which is returned directly (without being evaluated).

So it is expected that "quote (1 2 3)" should be evaluated to "(1 2 3)".

On the other hand, according to test 6:

assert_equals([1, 2, 3, True], evaluate(parse("'(1 2 3 #t)"), Environment()))

As far as I understand, ' is a shorthand for quote, so it should be evaluated to "(1 2 3 #t)"

Import statements -- qualify with diylisp?

My initial attempt at running tests gave me the following error (following from the instructions):

kevinushey@Kevin-MBP:~/git/diy-lisp$ nosetests tests/test_1_parsing.py --stop

======================================================================
ERROR: Failure: ImportError (cannot import name 'is_boolean')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python3.4/site-packages/nose/failure.py", line 39, in runTest
    raise self.exc_val.with_traceback(self.tb)
  File "/usr/local/lib/python3.4/site-packages/nose/loader.py", line 414, in loadTestsFromName
    addr.filename, addr.module)
  File "/usr/local/lib/python3.4/site-packages/nose/importer.py", line 47, in importFromPath
    return self.importFromDir(dir_path, fqname)
  File "/usr/local/lib/python3.4/site-packages/nose/importer.py", line 94, in importFromDir
    mod = load_module(part_fqname, fh, filename, desc)
  File "/usr/local/Cellar/python3/3.4.0_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/imp.py", line 235, in load_module
    return load_source(name, filename, file)
  File "/usr/local/Cellar/python3/3.4.0_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/imp.py", line 171, in load_source
    module = methods.load()
  File "<frozen importlib._bootstrap>", line 1220, in load
  File "<frozen importlib._bootstrap>", line 1200, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 1129, in _exec
  File "<frozen importlib._bootstrap>", line 1448, in exec_module
  File "<frozen importlib._bootstrap>", line 321, in _call_with_frames_removed
  File "/Users/kevinushey/git/diy-lisp/tests/test_1_parsing.py", line 5, in <module>
    from diylisp.parser import parse, unparse
  File "/Users/kevinushey/git/diy-lisp/diylisp/parser.py", line 4, in <module>
    from ast import is_boolean, is_list
ImportError: cannot import name 'is_boolean'

Should we be using from diylisp.ast import ... instead; ie, qualifying with the directory?

(My lack of proficiency with Python is probably showing here...)

kvalle / diy-lang Goto Github PK

diy-lang's People

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diy-lang's Issues

Question about scopes / environments

Parser tests don't cover ints

Why is eq working only on atoms?

Missing license

repl broken in Python 2

Solution tests fails

The ' (quote) symbol is not well defined

Import statements -- qualify with diylisp?

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