trivial

WARNING: things are current in a heavy development state. See the 6.4 release branch for a stable version.

This Typed Racket library provides "smarter" versions of standard library functions. For example:

#lang typed/racket/base

(require trivial)

(printf: "hello, ~a")

;; > raco make test.rkt
;; format:: arity mismatch;
;;  the expected number of arguments does not match the given number
;;    expected: 1
;;      given: 0

The printf: (with a colon) checks whether its first argument is a string literal. If so, it parses the string's format sequences for arity and type constraints.

Definitions work too:

(require trivial/no-colon)

(let ([s "hello ~a"])
  (printf s))

When the first argument to printf: is not clear from the program syntax, nothing special happens; we just call the standard printf.

#lang typed/racket/base

(require trivial)

((lambda ([s : String])
  (printf: s)) ;; Non-trivial!
 "hello, ~a\n")

;; Compiles successfully, but throws arity error at runtime

Besides printf:, this library also provides macros for:

• regexp-match:, to count the number of groups in a pattern and give the match result a more specific type
• constant-folding arithmetic, so (/ 1 0) raises a compile-time error
• arity-aware functions, like generalized curry and map
• size-aware vector functions, like length-propagating vector-append
• (experimental) typed database queries

See the documentation for the full story.

trivial is not currently compatible with untyped Racket.

Install

From Github:

> git clone https://github.com/bennn/trivial
> raco pkg install ./trivial/trivial

From the Racket package server:

> raco pkg install trivial

Use (require trivial) to import all bindings from this library. If you get tired of writing colons everywhere, require trivial/no-colon instead.

Naming

• The library is "trivial" because it solves only the simplest typechecking problems, and does so simply by analyzing a local chunk of source code.

• By convention, we suffix all our exports with a trailing colon. This is a hint that the macro will attempt some extra static analysis (including typechecking) at its call-site.

Contributing

The perfect feature request would start like:

"Typed Racket rejects this program, but it is obviously well-typed because ..."

If the right type really is obvious, syntactically, we'll extend this library.