That is really cool!
On Mon, May 20, 2013 at 6:08 PM, Guillaume Marceau <gmarc...@gmail.com>wrote: > Hi all, > > > In case this might interest some folks here. I now work for a start up in > New York. We're doing physics-based analysis of green buildings. I just > received permission to release our JavaScript implementation of Racket's > contracts under an open source license, MPL to be precise. > > https://github.com/sefaira/rho-contracts.js > > > After some fiddling, I was able to create a syntax that's readable enough > (I hope). Here is the `derive` function wrapped in a contract: > > var c = require('contract') > > // define the contract that's used below (since it's used twice): > c.numberToNumber = c.fun( { x: c.number } ).returns(c.number) > > // derive: returns a function that is the numerically-computed derivative > // of the given function. > var derive = > /* This is the specification: */ > c.fun( { fn: c.numberToNumber }, > { deltaX: c.number } ) > .returns(c.numberToNumber) > .wrap( > /* And the implementation goes here: */ > function(fn, deltaX) { > return function(x) { > return (fn(x+deltaX/2) - fn(x-deltaX/2))/deltaX > } > }) > > > Once the contract is in place, you get the kind of error message you > always wanted to have in JavaScript, but never could, such as the basic > "wrong number of arguments.", and you also get contract error with blame > (though only function-level blame, not between-module blame): > > // Error: forgetting an argument: > > derive(quadratic) > ContractError: Wrong number of arguments, expected 2 but got 1 > > // Error: calling with the arguments flipped: > > derive(1.0, quadratic) > ContractError: Expected fun, but got 1 > For the `fn` argument of the call. > > // Error: calling with the wrong kind of function: > > var d = derive(function(x) { return "**" + x + "**" }, 1.0) > > // The contract-checking shell is now installed around `fn` inside of > `d`; > // throws an error when called: > > d(100) > ContractError: `fn()` broke its contract > Expected number, but got '**100.5**' > for the return value of the call. > > > > There is also support for placing contract on whole module at a time. > Notably, the contract library itself is wrapped with contracts, as it > should: > > https://github.com/sefaira/rho-contracts.js/blob/master/contract.face.js > > > This has been in production at sefaira.com for about a year now. We're > really happy to have a piece of Racket-lore be our first open source > release. Hopefully there will be more. > > > Best, > > Guillaume > > > > > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > >
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