105 lines
2.8 KiB
Markdown
105 lines
2.8 KiB
Markdown
trivial
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===
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[](https://travis-ci.org/bennn/trivial)
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[](https://coveralls.io/github/bennn/trivial?branch=master)
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[](http://pkg-build.racket-lang.org/doc/trivial/index.html)
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This [Typed Racket](http://docs.racket-lang.org/ts-reference/) library provides "smarter" versions of standard library functions.
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For example:
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```
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#lang typed/racket/base
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(require trivial)
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(printf: "hello, ~a")
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;; > raco make test.rkt
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;; format:: arity mismatch;
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;; the expected number of arguments does not match the given number
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;; expected: 1
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;; given: 0
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```
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The `printf:` (with a colon) checks whether its first argument is a string literal.
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If so, it parses the string's format sequences for arity and type constraints.
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Definitions work too:
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```
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(require trivial/no-colon)
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(let ([s "hello ~a"])
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(printf s))
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```
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When the first argument to `printf:` is not clear from the program syntax, nothing special happens; we just call the standard `printf`.
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```
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#lang typed/racket/base
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(require trivial)
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((lambda ([s : String])
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(printf: s)) ;; Non-trivial!
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"hello, ~a\n")
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;; Compiles successfully, but throws arity error at runtime
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```
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Besides `printf:`, this library also provides [macros](http://www.greghendershott.com/fear-of-macros/)
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for:
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- `regexp-match:`, to count the number of groups in a pattern and give the match result a more specific type
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- constant-folding arithmetic, so `(/ 1 0)` raises a compile-time error
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- arity-aware functions, like generalized `curry` and `map`
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- size-aware vector functions, like length-propagating `vector-append`
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- (experimental) typed database queries
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See the [documentation](http://pkg-build.racket-lang.org/doc/trivial/index.html) for the full story.
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`trivial` is not currently compatible with untyped Racket.
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Install
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---
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From Github:
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```
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> git clone https://github.com/bennn/trivial
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> raco pkg install ./trivial
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```
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From the Racket [package server](http://pkgs.racket-lang.org/):
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```
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> raco pkg install trivial
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```
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Use `(require trivial)` to import all bindings from this library.
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If you get tired of writing colons everywhere, require `trivial/no-colon` instead.
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Naming
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---
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- The library is "trivial" because it solves only the simplest typechecking problems, and does so simply by analyzing a local chunk of source code.
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- By convention, we suffix all our exports with a trailing colon.
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This is a hint that the macro will attempt some extra static analysis (including typechecking) at its call-site.
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Contributing
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---
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The perfect feature request would start like:
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"Typed Racket rejects this program, but it is obviously well-typed because ..."
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If the right type really is obvious, syntactically, we'll extend this library.
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