Groovy DSL examples, see https://sandstorm.de/de/blog/post/how-to-create-a-dsl-with-groovy.html

BetterBouquetDsl.groovy

// our configuration model
class BouquetConfiguration extends ArrayList<String> {
    
    int howMany(String flower) {
        return this.count { it == flower }
    }
    
    String toString() {
        return "Bouquet: " + this.toString()
    }
}

// our DSL keyword
class BouquetConfigurationDsl {
    private final BouquetConfiguration bouquet
    
    BouquetConfigurationDsl(BouquetConfiguration bouquet) {
        this.bouquet = bouquet
    }
    
    void flower(String flower) {
        bouquet << flower
    }
}

class Bouquet {
    static BouquetConfiguration create(
        @DelegatesTo(strategy = Closure.DELEGATE_FIRST, value = BouquetConfigurationDsl) Closure script
    ) {
        def bouquet = new BouquetConfiguration()
        script.resolveStrategy = Closure.DELEGATE_ONLY
        script.delegate = new BouquetConfigurationDsl(bouquet)
        script()
        return bouquet
    }
}

def bouquet = Bouquet.create {
    flower "cornflower"
    flower "cornflower"
    flower "poppy"
    flower "calendula"
}

println bouquet

BouquetDsl.groovy

// our configuration model
class BouquetConfiguration {
    private final List<String> flowers = []
    
    // method for use at runtime
    int howMany(String flower) {
        return flowers.count { it == flower }
    }
    
    // DSL keyword for use at DSL execution
    void flower(String flower) {
        flowers << flower
    }
    
    String toString() {
        return "Bouquet: " + flowers.toString()
    }
}

class Bouquet {
    static BouquetConfiguration create(
        @DelegatesTo(strategy = Closure.DELEGATE_FIRST, value = BouquetConfiguration) Closure script
    ) {
        def bouquet = new BouquetConfiguration()
        script.resolveStrategy = Closure.DELEGATE_ONLY
        script.delegate = bouquet
        script()
        return bouquet
    }
}

def bouquet = Bouquet.create {
    flower "cornflower"
    flower "cornflower"
    flower "poppy"
    flower "calendula"
}

println bouquet

FloristDsl.groovy

class BouquetConfiguration extends ArrayList<String> {
    
    int howMany(String flower) {
        return this.count { it == flower }
    }
    
    String toString() {
        return "Bouquet: " + this.toString()
    }
}

class FloristConfiguration {
    final Map<String, BouquetConfiguration> catalog = [:]
    
    String toString() {
        return "Florist: " + catalog.toString()
    }
}

class BouquetConfigurationDsl {
    private final BouquetConfiguration bouquet
    
    BouquetConfigurationDsl(BouquetConfiguration bouquet) {
        this.bouquet = bouquet
    }
    
    void flower(String flower) {
        bouquet << flower
    }
}

class FloristConfigurationDsl {
    private final FloristConfiguration florist
    
    FloristConfigurationDsl(FloristConfiguration florist) {
        this.florist = florist
    }
    
    BouquetConfiguration bouquet(
        String name,
        @DelegatesTo(strategy = Closure.DELEGATE_FIRST, value = BouquetConfigurationDsl) Closure script
    ) {
        def bouquet = florist.catalog[name]
        if (bouquet == null) {
            bouquet = florist.catalog[name] = new BouquetConfiguration()
        }
        script.resolveStrategy = Closure.DELEGATE_ONLY
        script.delegate = new BouquetConfigurationDsl(bouquet)
        script()
        return bouquet
    }
}

class Florist {
    static FloristConfiguration create(
        @DelegatesTo(strategy = Closure.DELEGATE_FIRST, value = FloristConfigurationDsl) Closure script
    ) {
        def florist = new FloristConfiguration()
        script.resolveStrategy = Closure.DELEGATE_ONLY
        script.delegate = new FloristConfigurationDsl(florist)
        script()
        return florist
    }
}

def florist = Florist.create {

    bouquet "meadow", {
        flower "cornflower"
        flower "cornflower"
        flower "poppy"
        flower "calendula"
    }

    bouquet "roses", {
        flower "rose"
        flower "rose"
        flower "rose"
        flower "rose"
    }

    // add another calendula to existing bouquet
    bouquet "meadow", {
        flower "calendula"
    }
}

println florist

HelloWorldDsl.groovy

class HelloWorldService {
	// this function becomes a keyword in our DSL
    void printHelloWorld() {
        println("Hello World")
    }
}

class HelloWorldScript {
    static void execute(Closure script) {
    	// here we wire the colure with the service
        script.delegate = new HelloWorldService()
        
        // i explain this line in a later example ;)
        script.resolveStrategy = Closure.DELEGATE_ONLY
        
        // the closure is executed in the context of its delegate
        script()
    }
}

HelloWorldScript.execute {
    printHelloWorld()
    
    for(def i = 0; i < 10; i++) {
        printHelloWorld()
    }
}

HighlightedHelloWorldDsl.groovy

class HelloWorldService {
    void printHelloWorld() {
        println("Hello World")
    }
}

class HelloWorldScript {
	// by annotating the parameter we gain syntax highlighting and auto-completion
    static void execute(@DelegatesTo(strategy = Closure.DELEGATE_FIRST, value = HelloWorldService) Closure script) {
        script.resolveStrategy = Closure.DELEGATE_ONLY
        script.delegate = new HelloWorldService()
        script()
    }
}

HelloWorldScript.execute {
    printHelloWorld()
    
    for(def i = 0; i < 10; i++) {
        printHelloWorld()
    }
}