Marijn Schouten edited this page Sep 13, 2018 · 41 revisions

A wishlist of backwards incompatible things for a future Racket2.

Note: This is a wishlist. There's no guarantee any of these will be in a Racket2.

  • Drop more guarantees about new object allocations: for example, allow (append lst '()) to return lst, and the same for other list, string, bytes, vector functions (drop 0 items from the end of a list, substring and regexp-replace that don't change a string, etc).

  • Remove cond's default else-is-void clause and replace with a default else-is-error.

  • Change match to recognize clauses based on bindings instead of symbols, and make it treat else like cond.

  • Make every place where binding variables currently appear allow arbitrary match patterns (this requires some thought for handling what is currently things like (define (f x) ..), so maybe we do this in a more limited way or change that way of defining functions to use a new keyword)

  • Building on the match allowance, also allow functions to be defined case-by-case, for example maybe using a notation like this (roughly allowed in all internal definition contexts where := is the keyword that triggers this kind of parsing):

      (length '()) := 0
      (length (cons x y)) := (+ 1 (len y))

And, even better, have this turn into define/contract or maybe provide/contract if something like this is written:

    length : (-> list? exact-nonnegative-integer?)
    (length '()) := 0
    (length (cons x y)) := (+ 1 (len y))
  • Consider changing cond (and match) to use #:else instead of else.

  • More prefabs for basic values, especially ones like srclocs where it is useful to make cross phase movements easy.

  • Enable internal definitions everywhere. (Note: this is tricky -- what's "everywhere"? Eg, can define id be followed by a definition(s) and then a value? How about in the middle of an if? Taken to an extreme, could definitions appear in an application form?)

  • change syntax-case to allow internal definitions (possibly by getting rid of the 'guard' section)

  • Enable the define* form (from racket/package) everywhere

  • Use keywords in more places, such as unifying member, memv, memf, etc.

  • Some syntax that avoids the verbosity in the keyword-apply etc kind of functions in the common case of passing keywords around.

  • Some solution to the "no-value" value, which could be such a blessed value, or it could be a way to say that some function accepts all the keywords as some other function. (Possibly related to the above, of course.)

  • struct definition macro that allows

    • naming of the accessors/constructors/etc
    • per-field #:auto values
    • creating a constructor that takes all fields (when #:auto values should be something different)
    • creating a constructor that makes #:auto fields optional keyword arguments
    • make struct have a function-like form that can specify auto values as optionals and/or keywords
    • maybe even allow several constructors with different argument "shapes"
    • more ideas from CL, like a struct keyword that actually use (tagged) lists for the values, similar to prefabs (and possibly redundant because of them)
    • like sstruct2
  • Have only either struct or define-struct. Not both.

  • Disallow mutation of struct bindings.

  • include pattern matching forms in more binding positions (e.g. define, let/for clauses)

  • Generic programming by default: map, fold, and friends are generic and not specialized to lists.

  • Change integer? to mean exact-integer?.

  • Get rid of the arity-at-least struct, and replace it with just an arity that abstracts over the whole arity thing -- always normalizing and includes keyword arity information. Also, make it possible to always use a procedure where an arity is expected.

  • Reconsider printing and equality of mutable and immutable variants of data types (vectors, hash tables, strings, etc.). Also reconsider the coercion of mutable vectors to immutable vectors by datum->syntax.

  • Add CLOS-like defmethod (with multidispatch and :before, :after, :around) on Racket classes.

  • Add interactive breakpoint in DrRacket debug. One should have REPL at breakpoint

  • Make strings immutable.

  • Have with-output-to-string and friends take a body, not a thunk. The current form is better named call-with-output-to-string, in the general pattern of with-x being syntax and call-with-x being a procedure.

  • Have <, > and others take 0 or more arguments (returning #t for the 0 and 1 argument cases). This would allow applying them to lists without fear, which would allow patterns like (define (sorted? l) (apply < l))

  • Rename racket/cmdline to racket/command-line.

  • Require that macro literals always be bound.

  • Make Matthew's doc-define from ClojureWest keynote real

  • Consider having real identifiers for class/object members and use the module/namespace mechanisms to manage these references. Possibly in conjunction with a convention for names that are prefixed or included in others (so that we can have identifiers like frame%:show treated specially). Potentially makes method invocation faster and allows static detection of method-not-found errors.

  • Have quasiquote support ... as well as ,@. Among other things, this lets match patterns can be like match "templates" (output expressions) and be like syntax-case etc.

  • [tonyg] The .zo and .dep files should be invisible to the user. They should be created, deleted, invalidated, and processed generally without needing to form part of the user's mental model or workflow. Look at how python does this. It'd be lovely to make explicit calls to raco make (or even raco setup??) unnecessary.

  • [jackfirth] Use syntax parameters in for loops for break and continue instead of keywords

  • [alexis king] Make all of match’s patterns properly hygienic, rather than inspecting datums for the primitive pattern-matching constructs.

  • [gus-massa] The values returned by make-custom-hash-types and make-custom-set-types have a different order. Change one of them to improve consistency.

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