tov/dssl2

A data structures student language, version 2

dssl2's Issues

Bad Error Message for Use Before Definition

This program:

#lang dssl2

def fun():
    helper()
    def helper():
        return 0
fun()

produces the error:

real-definition: undefined;
 cannot use before initialization

without a useful source location.

real-definition looks like some internal name leaking, but the name from the program would be better.

Dssl2 Installation Issues

raco pkg install dssl2

I've recently updated racket from 7.8.2 to 7.9.1 when updating my system.
Upon running any dssl2 script, I get:

standard-module-name-resolver: collection not found
  for module path: dssl2/lang/reader
  collection: "dssl2/lang"
  in collection directories:
   /home/marko/.racket/7.9/collects
   /usr/share/racket/collects
   ... [161 additional linked and package directories]

I've tried running raco pkg install dssl2, which threw:

Resolving "dssl2" via https://download.racket-lang.org/releases/7.9/catalog/
raco pkg install: cannot find package on catalogs
  package: dssl2

curl https://download.racket-lang.org/releases/7.9/catalog/ gives a text/html 404.

This might be a racket catalog issue, but I've skimmed their package catalog on GitHub (not sure if this is the right place), without any results. I've tried running:

grep -r -i dssl2 .
grep -r -i "jesse\.tov" .
grep -r -i northwestern .

where cwd is the master branch of the release catalog, commit adadb82, with no matches.

raco pkg install -t github tov/dssl2

raco pkg install -t github tov/dssl2 and raco pkg install https://github.com/tov/dssl2.git also don't work, being unhappy with the master branch name change to main. The error thrown is:

Querying Git references for dssl2 at git://github.com/tov/dssl2
git: could not find requested reference
  reference: master
  repo: tov/dssl2
  context...:
   /usr/share/racket/collects/net/git-checkout.rkt:359:0: select-commits
   /usr/share/racket/collects/net/git-checkout.rkt:73:8
   /usr/share/racket/collects/net/git-checkout.rkt:54:2: retry-loop
   /usr/share/racket/collects/pkg/private/stage.rkt:59:2: lookup-normally
   /usr/share/racket/collects/pkg/private/stage.rkt:107:0: stage-package/info
   /usr/share/racket/collects/pkg/private/install.rkt:141:0: install-packages
   /usr/share/racket/collects/pkg/private/install.rkt:925:4
   /usr/share/racket/collects/racket/contract/private/arrow-val-first.rkt:555:3
   /usr/share/racket/collects/racket/file.rkt:437:8
   /usr/share/racket/collects/racket/file.rkt:426:0: call-with-file-lock
   /usr/share/racket/collects/pkg/main.rkt:216:16
   (submod "/usr/share/racket/collects/pkg/main.rkt" main): [running body]
   "/usr/share/racket/collects/raco/raco.rkt": [running body]
   "/usr/share/racket/collects/raco/main.rkt": [running body]

I did get things to work by manually cloning dssl2 manually and manually installing it with raco, but, more importantly I checked whether DrRacket would install dssl2 well (as most people wouldn't probably know how to manually clone repos and would just follow the guide off the README) and it didn't, throwing the same error.

I suggest leaving the master branch name as a secondary branch until racket fixes their master-referring code.

Other info

Racket: 7.9.1
OS: Arch, latest

Nested Higher-Order Contract Oddities

Appears to require at least one of them to be defined in DSSL2 code (i.e, not built in).

#lang dssl2

class NotVec[K]:
    def __init__(self):
        pass

# this works
def foo(x: NotVec?):
    pass
foo(NotVec[VecC[num?]]())

# this works too
def foo2(x: NotVec?[num?]):
    pass
foo2(NotVec[num?]())

# this does not, contract violation
def foo3(x: NotVec?[VecC[num?]]):
    pass
foo3(NotVec[VecC[num?]]())

# this also works, different higher-order contract
def bar (x: FunC[num?, num?]):
    pass
bar(λ x: x)

Very first example in the docs is not working DSSL2

The very first DSSL2 code example in the docs (root insertion in a BST) refers to a number of undefined functions (e.g., empty?, new_node, fix_size).
So it's not actually a working example that someone could just copy and run.
That's not great for the first example someone sees...

Especially confusing is the use of empty?, which looks like a function that could plausibly be provided by the language. I just had a student assume (possibly based on that example) that DSSL2 provided an empty? function, which it does not.

Varargs functions and varargs application

def sum(*args):
    let res = 0
    for a in args: res = res + a
    return res

assert_eq sum(1, 2, 3, 4), 10
assert_eq sum(1, *[2, 3, 4]), 10

Classes should be contracts

Let's get rid of predicates like int? and use the int class instead. Examples:

def f(x: int) -> int:
    …

if isinstance(y, int):
    …

Inline Struct Literals

The language does not appear to support inline struct literal construction syntax.

This statement does not work:

let customers = [
    customer { name: 'Alice', bank_account: Account(1, 'savings', 10) },
    customer { name: 'Bob', bank_account: Account(2, 'checking', 5) }
]

The following error is thrown:

hw1.rkt:163:8: Syntax error: unexpected token ‘customer’
  context...:
   /usr/share/racket/collects/syntax/readerr.rkt:6:2: raise-read-error
   /usr/share/racket/pkgs/parser-tools-lib/parser-tools/yacc.rkt:347:16: parsing-loop
   /usr/share/racket/collects/syntax/module-reader.rkt:186:17: body
   /usr/share/racket/collects/syntax/module-reader.rkt:183:2: wrap-internal
   lang:read-syntax
   read-syntax
   default-load-handler
   standard-module-name-resolver
   module-path-index-resolve
   [repeats 1 more time]
   module-declared?

However, this syntax works, throwing no errors:

let c1 = customer { name: 'Alice', bank_account: Account(1, 'savings', 10) }
let c2 = customer { name: 'Bob', bank_account: Account(2, 'checking', 5) }

let customers = [c1, c2]

Also, please observe that the following will throw an error:

let customers = [
    { name: 'Alice', bank_account: Account(1, 'savings', 10) },
    { name: 'Bob', bank_account: Account(2, 'checking', 5) }
]

That error is:

hw1.rkt:155:8: Syntax error: unexpected token ‘LBRACE’
  context...:
   /usr/share/racket/collects/syntax/readerr.rkt:6:2: raise-read-error
   /usr/share/racket/pkgs/parser-tools-lib/parser-tools/yacc.rkt:347:16: parsing-loop
   /usr/share/racket/collects/syntax/module-reader.rkt:186:17: body
   /usr/share/racket/collects/syntax/module-reader.rkt:183:2: wrap-internal
   lang:read-syntax
   read-syntax
   default-load-handler
   standard-module-name-resolver
   module-path-index-resolve
   [repeats 1 more time]
   module-declared?

This appears to indicate that inline struct literal construction does not work. Note that class construction is also employed in this example and it does not present any issues to the interpreter.

Perhaps it would be beneficial and would be a QOL upgrade to enable inline struct construction.

Additional Information

• OS: Arch Linux, latest
• Racket Version: 7.8
• Dssl2 Verison: `release, commit 11f216aacbb71a6b13721e71f5ed583a19965e44.

Hard to define recursive contracts/structs

This code works:

    defstruct Node(
       prev: MaybeC(Node?),
       data: MaybeC(X),
       next: MaybeC(Node?))

But this code doesn't:

    defstruct Node(
       prev: Link,
       data: MaybeC(X),
       next: Link)
    let Link = MaybeC(Node?)

It fails, saying that Link is undefined.

Identifiers in code in documentation aren't linked

@codeblock produces linked identifiers for #lang racket code, but for some reason it doesn’t for #lang dssl2.

Multi-line comment/uncomment operations in DrRacket

It should be easy to (un)comment multiple lines at once in DrRacket.

Bad error message when accidentally setting a method

The following program:

#lang dssl2

class Foo:
    let length
    def __init__(self):
        pass
    def len(self):
        pass
    def bar(self):
        self.len = self.len + 1

Raises the error:

Racket v7.8/add-on/7.8/pkgs/dssl2/private/class-system.rkt:276:33: set!: cannot assign to def'd function or method                         
  in: (set! «Foo».len (+ (struct-ref self len) 1))

This is clearly an error; the student wanted to set the length field, but was trying to set the len method instead.
But it would be nice to have an actual error for that, rather than an internal error.

Bad Error Message with Dynamic Arrays

This program:

#lang dssl2
import array
let x = array()
x[0]

produces this internal error:

dssl-printer: format string did not match number of params
  format string:   'Array index out of bounds: ~a >= ~a'
  expected params: 0
  actual params:   2

Thanks to Sonam Ford for the test case.

Different behavior when compiled with `raco make`

Compiling with raco make makes it impossible to implement an interface in a different source file than where the interface is defined. In particular, objects of a class C that implements an interface I imported from another source file are not actually considered to implement interface I by the I? and I! contracts.

How to reproduce

1. Create a file lib.rkt containing:

   #lang dssl2
   
   interface I: pass

2. Create a file client.rkt containing:

   #lang dssl2
   
   import 'lib.rkt'
   
   class C (I):
       def __init__(self): pass
   
   # This should succeed because C implements I, but it fails if you run
   # `raco make` first. (It also fails in DrRacket.)
   let o: I! = C()

3. Run client.rkt:

   $ racket client.rkt
   $

4. Compile client.rkt and run it again:

   $ raco make client.rkt
   $ racket client.rkt
   o: broke its own contract;
    class C does not implement interface I
     in: I!
     contract from: (definition o)
     blaming: (definition o)
      (assuming the contract is correct)
     at: /Users/tov/Desktop/raco-make-weirdness/client.rkt:10.4
     context...:
      /Applications/Racket v7.4/collects/racket/contract/private/blame.rkt:347:0: raise-blame-error16
      "/Users/tov/Desktop/raco-make-weirdness/client.rkt": [running body]
      temp37_0
      for-loop
      run-module-instance!125
      perform-require!78
   $

5. Delete the compilation artifacts and run it again:

   $ rm -R compiled
   $ racket client.rkt
   $

NaN and infinity print as "+nan.0", "+inf.0", "-inf.0"

but they are read as "nan", "inf", and "-inf". This should be made to match.

Add op-assign operators such as `+=`, `-=`, etc.

We should be able to write:

def sum_vec(v: vec[int]):
    let res = 0
    for n in v: res += n
    res

Error message for `range` is leaky

The code range([1,2])
results in the error

range: contract violation
  expected: num?
  given: [1, 2]
  in: the 1st argument of
      the 3rd case of
      (case->
       (-> num? num? num? AnyC)
       (-> num? num? AnyC)
       (-> num? AnyC))

This is the correct contract for DSSL's range, but having an error message in terms of case-> and prefix -> isn't ideal.

Strings print exotic characters with Racket's "\uXXXXX" syntax

which is not accepted by DSSL2. We should either change how strings are printed or accept that syntax as well.

source location wrong in vector indexing error

This program:

#lang dssl2
let x = [1,2,3]
x[[1,2]]

produces this error:

. . git/exp/plt/racket/share/pkgs/dssl2/private/syntax.rkt:418:7: «vec».__index_ref__: contract violation
  expected: nat?
  given: [1, 2]
  in: the 1st argument of
      (-> nat? AnyC)
  contract from: «vec».__index_ref__
  blaming: method caller
   (assuming the contract is correct)
  at: /Users/robby/tmp.rkt:3:0

which has a source location inside dssl2 instead of inside the dssl2 program.

Grader tests fail in terminal

Running raco test test/grader.rkt or racket test/grader.rkt fails, whereas running test/grader.rkt inside DrRacket works. When running these tests in the terminal the output suggests that the code under test, which is supposed to attempt several DSSL2 tests, isn’t attempting any. This Racket 7.8 on is on MacOS Big Sur, so it might be a permission issue.

Suboptimal error message when setting non-existing field

Consider this program:

#lang dssl2
class Foo[X]:
    let _data
    def __init__(self):
        self.data = 10 # wrong var name

which produces the error:

bug-hw5.rkt:7:13: set!: unbound identifier
  at: «Foo».data
  in: (set! «Foo».data 10)

That error message isn't too bad (it clearly shows the field name at fault), but the fact that it it's terms of set! isn't great.

FWIW, that happens only for class fields. Not for either local or global variables.

Documentation for standard library

Standard library modules such as cons and sbox_hash should be documented.

Fix tests for grader.

The tests for the grader fail when run from the command line but succeed
in DrRacket. Why?

All functions print as "...e/parametric.rkt:82:10"

This is because parametric->/c isn't nice about how it wraps its argument, I suppose. Is there a way to get the right name on it?

source location wrong in runtime error

In this program:

#lang dssl2

class C:
     let fd
     def __init__(self):
         self.fd == None
         
C()

the error message points inside the class system. Changing this code to:

(syntax/loc stx ...)

where the ellipses has what's currently on those lines (minus the #') seems to fix the issue.