Introduce variable filters

README.md

@@ -1,5 +1,4 @@
-Stencil
-=======
+# Stencil
 
 [![Build Status](http://img.shields.io/circleci/project/kylef/Stencil/master.svg)](https://circleci.com/gh/kylef/Stencil)
 
@@ -7,7 +6,7 @@ Stencil is a simple and powerful template language for Swift. It provides a
 syntax similar to Django and Mustache. If you're familiar with these, you will
 feel right at home with Stencil.
 
-### Example
+## Example
 
 ```html+django
 There are {{ articles.count }} articles.
@@ -78,6 +77,53 @@ There are {{ people.count }} people, {{ people.first }} is first person.
 Followed by {{ people.1 }}.
 ```
 
+#### Filters
+
+Filters allow you to transform the values of variables. For example, they look like:
+
+```html+django
+{{ variable|uppercase }}
+```
+
+##### Capitalize
+
+The capitalize filter allows you to capitalize a string.
+For example, `stencil` to `Stencil`.
+
+```html+django
+{{ "stencil"|capitalize }}
+```
+
+##### Uppercase
+
+The uppercase filter allows you to transform a string to uppercase.
+For example, `Stencil` to `STENCIL`.
+
+```html+django
+{{ "Stencil"|uppercase }}
+```
+
+##### Lowercase
+
+The uppercase filter allows you to transform a string to lowercase.
+For example, `Stencil` to `stencil`.
+
+```html+django
+{{ "Stencil"|lowercase }}
+```
+
+#### Registering custom filters
+
+```
+template.parser.registerFilter("double") { value in
+  if let value = value as? Int {
+    return value * 2
+  }
+
+  return value
+}
+```
+
 ### Tags
 
 Tags are a mechanism to execute a piece of code, allowing you to have

Stencil.xcodeproj/project.pbxproj

@@ -11,6 +11,8 @@
 		27A848E91B42242C004ACA13 /* base.html in Resources */ = {isa = PBXBuildFile; fileRef = 27A848E71B42242C004ACA13 /* base.html */; };
 		27A848EA1B42242C004ACA13 /* child.html in Resources */ = {isa = PBXBuildFile; fileRef = 27A848E81B42242C004ACA13 /* child.html */; };
 		27A848EC1B42247D004ACA13 /* InheritenceTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 27A848EB1B42247D004ACA13 /* InheritenceTests.swift */; };
+		27BA0A9E1BD9465700B7209B /* Filters.swift in Sources */ = {isa = PBXBuildFile; fileRef = 27BA0A9D1BD9465700B7209B /* Filters.swift */; settings = {ASSET_TAGS = (); }; };
+		27BA0AA01BD946C300B7209B /* FilterTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 27BA0A9F1BD946C300B7209B /* FilterTests.swift */; settings = {ASSET_TAGS = (); }; };
 		27CE0ADE1A50BEC3004A105B /* TemplateLoader.swift in Sources */ = {isa = PBXBuildFile; fileRef = 27CE0ADD1A50BEC3004A105B /* TemplateLoader.swift */; };
 		27CE0AE01A50BF05004A105B /* TemplateLoaderTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 27CE0ADF1A50BF05004A105B /* TemplateLoaderTests.swift */; };
 		27CE0AFA1A50C963004A105B /* test.html in Resources */ = {isa = PBXBuildFile; fileRef = 27CE0AF91A50C963004A105B /* test.html */; };
@@ -53,6 +55,8 @@
 		27A848E71B42242C004ACA13 /* base.html */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.html; path = base.html; sourceTree = "<group>"; };
 		27A848E81B42242C004ACA13 /* child.html */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.html; path = child.html; sourceTree = "<group>"; };
 		27A848EB1B42247D004ACA13 /* InheritenceTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = InheritenceTests.swift; sourceTree = "<group>"; };
+		27BA0A9D1BD9465700B7209B /* Filters.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Filters.swift; sourceTree = "<group>"; };
+		27BA0A9F1BD946C300B7209B /* FilterTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FilterTests.swift; sourceTree = "<group>"; };
 		27CE0ADD1A50BEC3004A105B /* TemplateLoader.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TemplateLoader.swift; sourceTree = "<group>"; };
 		27CE0ADF1A50BF05004A105B /* TemplateLoaderTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = TemplateLoaderTests.swift; sourceTree = "<group>"; };
 		27CE0AF91A50C963004A105B /* test.html */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = text.html; path = test.html; sourceTree = "<group>"; };
@@ -149,6 +153,7 @@
 			children = (
 				77FAAE5719F91E480029DC5E /* Stencil.h */,
 				77FAAE6E19F920750029DC5E /* Context.swift */,
+				27BA0A9D1BD9465700B7209B /* Filters.swift */,
 				77EB082A19FA8600001870F1 /* Lexer.swift */,
 				7725B3D419F9438F002CF74B /* Node.swift */,
 				7725B3D619F94A43002CF74B /* Parser.swift */,
@@ -177,6 +182,7 @@
 				77FAAE7019F9208C0029DC5E /* ContextTests.swift */,
 				7725B3CA19F92B4F002CF74B /* VariableTests.swift */,
 				7725B3D219F9437F002CF74B /* NodeTests.swift */,
+				27BA0A9F1BD946C300B7209B /* FilterTests.swift */,
 				7725B3D819F94A61002CF74B /* ParserTests.swift */,
 				77EB082819FA85F2001870F1 /* LexerTests.swift */,
 				77EB082619F96E9C001870F1 /* TemplateTests.swift */,
@@ -416,6 +422,7 @@
 				77FAAE6F19F920750029DC5E /* Context.swift in Sources */,
 				77EB082B19FA8600001870F1 /* Lexer.swift in Sources */,
 				7725B3CF19F94214002CF74B /* Tokenizer.swift in Sources */,
+				27BA0A9E1BD9465700B7209B /* Filters.swift in Sources */,
 				7725B3D719F94A43002CF74B /* Parser.swift in Sources */,
 				77EB082519F96E88001870F1 /* Template.swift in Sources */,
 				7725B3CD19F92B61002CF74B /* Variable.swift in Sources */,
@@ -437,6 +444,7 @@
 				77EB082719F96E9C001870F1 /* TemplateTests.swift in Sources */,
 				7725B3CB19F92B4F002CF74B /* VariableTests.swift in Sources */,
 				27CE0B041A50CBEA004A105B /* IncludeTests.swift in Sources */,
+				27BA0AA01BD946C300B7209B /* FilterTests.swift in Sources */,
 				77EB082919FA85F2001870F1 /* LexerTests.swift in Sources */,
 				77FAAE7119F9208C0029DC5E /* ContextTests.swift in Sources */,
 			);

Stencil/Filters.swift

@@ -0,0 +1,33 @@
+func toString(value: Any?) -> String? {
+  if let value = value as? String {
+    return value
+  } else if let value = value as? CustomStringConvertible {
+    return value.description
+  }
+
+  return nil
+}
+
+func capitalise(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.capitalizedString
+  }
+
+  return value
+}
+
+func uppercase(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.uppercaseString
+  }
+
+  return value
+}
+
+func lowercase(value: Any?) -> Any? {
+  if let value = toString(value) {
+    return value.lowercaseString
+  }
+
+  return value
+}

Stencil/Node.swift

@@ -46,10 +46,14 @@ public class TextNode : NodeType {
   }
 }
 
-public class VariableNode : NodeType {
-  public let variable:Variable
+public protocol Resolvable {
+  func resolve(context: Context) -> Any?
+}
 
-  public init(variable:Variable) {
+public class VariableNode : NodeType {
+  public let variable: Resolvable
+
+  public init(variable: Resolvable) {
     self.variable = variable
   }
 
@@ -58,10 +62,12 @@ public class VariableNode : NodeType {
   }
 
   public func render(context: Context) throws -> String {
-    let result:AnyObject? = variable.resolve(context)
+    let result = variable.resolve(context)
 
     if let result = result as? String {
       return result
+    } else if let result = result as? CustomStringConvertible {
+      return result.description
     } else if let result = result as? NSObject {
       return result.description
     }
@@ -94,7 +100,7 @@ public class NowNode : NodeType {
 
   public func render(context: Context) throws -> String {
     let date = NSDate()
-    let format: AnyObject? = self.format.resolve(context)
+    let format = self.format.resolve(context)
     var formatter:NSDateFormatter?
 
     if let format = format as? NSDateFormatter {
@@ -212,7 +218,7 @@ public class IfNode : NodeType {
   }
 
   public func render(context: Context) throws -> String {
-    let result: AnyObject? = variable.resolve(context)
+    let result = variable.resolve(context)
     var truthy = false
 
     if let result = result as? [AnyObject] {

Stencil/Parser.swift

@@ -10,12 +10,15 @@ public func until(tags:[String])(parser:TokenParser, token:Token) -> Bool {
   return false
 }
 
+public typealias Filter = Any? -> Any?
+
 /// A class for parsing an array of tokens and converts them into a collection of Node's
 public class TokenParser {
   public typealias TagParser = (TokenParser, Token) throws -> NodeType
 
   private var tokens:[Token]
   private var tags = [String:TagParser]()
+  private var filters = [String: Filter]()
 
   public init(tokens:[Token]) {
     self.tokens = tokens
@@ -26,6 +29,9 @@ public class TokenParser {
     registerTag("include", parser: IncludeNode.parse)
     registerTag("extends", parser: ExtendsNode.parse)
     registerTag("block", parser: BlockNode.parse)
+    registerFilter("capitalize", filter: capitalise)
+    registerFilter("uppercase", filter: uppercase)
+    registerFilter("lowercase", filter: lowercase)
   }
 
   /// Registers a new template tag
@@ -40,6 +46,10 @@ public class TokenParser {
     })
   }
 
+  public func registerFilter(name: String, filter: Filter) {
+    filters[name] = filter
+  }
+
   /// Parse the given tokens into nodes
   public func parse() throws -> [NodeType] {
     return try parse(nil)
@@ -54,8 +64,8 @@ public class TokenParser {
       switch token {
       case .Text(let text):
         nodes.append(TextNode(text: text))
-      case .Variable(let variable):
-        nodes.append(VariableNode(variable: variable))
+      case .Variable:
+        nodes.append(VariableNode(variable: try compileFilter(token.contents)))
       case .Block:
         let tag = token.components().first
 
@@ -88,4 +98,16 @@ public class TokenParser {
   public func prependToken(token:Token) {
     tokens.insert(token, atIndex: 0)
   }
+
+  public func findFilter(name: String) throws -> Filter {
+    if let filter = filters[name] {
+      return filter
+    }
+
+    throw TemplateSyntaxError("Invalid filter '\(name)'")
+  }
+
+  func compileFilter(token: String) throws -> Resolvable {
+    return try FilterExpression(token: token, parser: self)
+  }
 }

Stencil/Variable.swift

@@ -1,8 +1,40 @@
 import Foundation
 
 
+class FilterExpression : Resolvable {
+  let filters: [Filter]
+  let variable: Variable
+
+  init(token: String, parser: TokenParser) throws {
+    let bits = token.componentsSeparatedByString("|")
+    if bits.isEmpty {
+      filters = []
+      variable = Variable("")
+      throw TemplateSyntaxError("Variable tags must include at least 1 argument")
+    }
+
+    variable = Variable(bits[0])
+    let filterBits = bits[1 ..< bits.endIndex]
+
+    do {
+      filters = try filterBits.map { try parser.findFilter($0) }
+    } catch {
+      filters = []
+      throw error
+    }
+  }
+
+  func resolve(context: Context) -> Any? {
+    let result = variable.resolve(context)
+
+    return filters.reduce(result) { x, y in
+      return y(x)
+    }
+  }
+}
+
 /// A structure used to represent a template variable, and to resolve it in a given context.
-public struct Variable : Equatable {
+public struct Variable : Equatable, Resolvable {
   public let variable:String
 
   /// Create a variable with a string representing the variable
@@ -15,11 +47,12 @@ public struct Variable : Equatable {
   }
 
   /// Resolve the variable in the given context
-  public func resolve(context:Context) -> AnyObject? {
+  public func resolve(context:Context) -> Any? {
     var current:AnyObject? = context
 
     if (variable.hasPrefix("'") && variable.hasSuffix("'")) || (variable.hasPrefix("\"") && variable.hasSuffix("\"")) {
-      return variable.substringWithRange(variable.startIndex.successor() ..< variable.endIndex.predecessor())
+      // String literal
+      return variable[variable.startIndex.successor() ..< variable.endIndex.predecessor()]
     }
 
     for bit in lookup() {

StencilTests/FilterTests.swift

@@ -0,0 +1,23 @@
+import XCTest
+import Stencil
+
+
+class FilterTests: XCTestCase {
+  func testCapitalizeFilter() {
+    let template = Template(templateString: "{{ name|capitalize }}")
+    let result = try? template.render(Context(dictionary: ["name": "kyle"]))
+    XCTAssertEqual(result, "Kyle")
+  }
+
+  func testUppercaseFilter() {
+    let template = Template(templateString: "{{ name|uppercase }}")
+    let result = try? template.render(Context(dictionary: ["name": "kyle"]))
+    XCTAssertEqual(result, "KYLE")
+  }
+
+  func testLowercaseFilter() {
+    let template = Template(templateString: "{{ name|lowercase }}")
+    let result = try? template.render(Context(dictionary: ["name": "Kyle"]))
+    XCTAssertEqual(result, "kyle")
+  }
+}

StencilTests/ParserTests.swift

@@ -17,13 +17,14 @@ class TokenParserTests: XCTestCase {
 
   func testParsingVariableToken() {
     let parser = TokenParser(tokens: [
-      Token.Variable(value: "name")
+      Token.Variable(value: "'name'")
     ])
 
     assertSuccess(try parser.parse()) { nodes in
       let node = nodes.first as! VariableNode
       XCTAssertEqual(nodes.count, 1)
-      XCTAssertEqual(node.variable, Variable("name"))
+      let result = try? node.render(Context())
+      XCTAssertEqual(result, "name")
     }
   }