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JSON Parsing in Swift
// This code accompanies a blog post: http://chris.eidhof.nl/posts/json-parsing-in-swift.html
//
// As of Beta5, the >>= operator is already defined, so I changed it to >>>=
import Foundation
let parsedJSON : [String:AnyObject] = [
"stat": "ok",
"blogs": [
"blog": [
[
"id" : 73,
"name" : "Bloxus test",
"needspassword" : true,
"url" : "http://remote.bloxus.com/"
],
[
"id" : 74,
"name" : "Manila Test",
"needspassword" : false,
"url" : "http://flickrtest1.userland.com/"
]
]
]
]
struct Blog {
let id: Int
let name: String
let needsPassword : Bool
let url: NSURL
}
func parseBlog(blog: AnyObject) -> Blog? {
let mkBlog = curry {id, name, needsPassword, url in Blog(id: id, name: name, needsPassword: needsPassword, url: url) }
return asDict(blog) >>>= {
mkBlog <*> int($0,"id")
<*> string($0,"name")
<*> bool($0,"needspassword")
<*> (string($0, "url") >>>= toURL)
}
}
func parseJSON() {
let blogs = dictionary(parsedJSON, "blogs") >>>= {
array($0, "blog") >>>= {
join($0.map(parseBlog))
}
}
println("posts: \(blogs)")
}
extension Blog : Printable {
var description : String {
return "Blog { id = \(id), name = \(name), needsPassword = \(needsPassword), url = \(url)"
}
}
func toURL(urlString: String) -> NSURL {
return NSURL(string: urlString)
}
func asDict(x: AnyObject) -> [String:AnyObject]? {
return x as? [String:AnyObject]
}
func join<A>(elements: [A?]) -> [A]? {
var result : [A] = []
for element in elements {
if let x = element {
result += [x]
} else {
return nil
}
}
return result
}
infix operator <*> { associativity left precedence 150 }
func <*><A, B>(l: (A -> B)?, r: A?) -> B? {
if let l1 = l {
if let r1 = r {
return l1(r1)
}
}
return nil
}
func flatten<A>(x: A??) -> A? {
if let y = x { return y }
return nil
}
func array(input: [String:AnyObject], key: String) -> [AnyObject]? {
let maybeAny : AnyObject? = input[key]
return maybeAny >>>= { $0 as? [AnyObject] }
}
func dictionary(input: [String:AnyObject], key: String) -> [String:AnyObject]? {
return input[key] >>>= { $0 as? [String:AnyObject] }
}
func string(input: [String:AnyObject], key: String) -> String? {
return input[key] >>>= { $0 as? String }
}
func number(input: [NSObject:AnyObject], key: String) -> NSNumber? {
return input[key] >>>= { $0 as? NSNumber }
}
func int(input: [NSObject:AnyObject], key: String) -> Int? {
return number(input,key).map { $0.integerValue }
}
func bool(input: [NSObject:AnyObject], key: String) -> Bool? {
return number(input,key).map { $0.boolValue }
}
func curry<A,B,R>(f: (A,B) -> R) -> A -> B -> R {
return { a in { b in f(a,b) } }
}
func curry<A,B,C,R>(f: (A,B,C) -> R) -> A -> B -> C -> R {
return { a in { b in {c in f(a,b,c) } } }
}
func curry<A,B,C,D,R>(f: (A,B,C,D) -> R) -> A -> B -> C -> D -> R {
return { a in { b in { c in { d in f(a,b,c,d) } } } }
}
infix operator >>>= {}
func >>>= <A,B> (optional : A?, f : A -> B?) -> B? {
return flatten(optional.map(f))
}
// This code is provided under the MIT license:
// Copyright (c) 2014 Chris Eidhof
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
@ryanbillingsley

@chriseidhof does this still work for you in Beta 5? I have a playground, and specifically the key to type conversion functions are not working

func array(input: [String:AnyObject], key: String) ->  [AnyObject]? {
    return input[key] >>= { $0 as? [AnyObject] }
}

Gives Error:

'String' is not convertible to 'DictionaryIndex<String,AnyObject>'
@ryanbillingsley

Never mind, it seems it simply didn't like how the >>= operator was being defined. It had to happen before it was used it or said it was being redeclared. Also, operator infix >>= {} is now infix operator >>= {} and you no longer use the @infix when defining the func >>= ...

@chriseidhof
Owner

Yes, thanks for the heads up! I just changed the gist, this works for me on Beta5 now.

@corinnekrych

Trying your code in beta6 (playground), line 52:

println("posts: \(blogs)")

does not properly call description, i replace it with:

if (blogs != nil) {
    for element in blogs! {
        println("posts: \(element.description)")
    }
}

I wonder why string interpolation does not call description by default of struct/class

@corinnekrych

Actually, browsing the forum https://devforums.apple.com/message/981127#981127
it seems an issue with playground and REPL only, ignore my previous comment.

@OscarSwanros

I'm having trouble getting this to work. Here's my JSON Dictionary:

[items: (
        {
        description = 123;
        id = 1;
        name = "iPone 4";
        why = 123;
    },
        {
        description = afasfdasfd13;
        id = 2;
        name = "iPhone 6";
        why = 23123123123;
    },
        {
        description = "";
        id = 3;
        name = "";
        why = "";
    }
)]

It crashes on

return asDict(item) >>>= {
    mkItem <*> int($0, "id")
           <*> string($0, "name")
           <*> string($0, "why")
}

With the message code EXC_I386_GPFLT.

What could be going wrong? I'm using Xcode 6.0.1

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