Test DSL Evaluator that doesn't work as I expected

DslEvaluator.groovy

class DslEvaluator {
    def methodMissing(String name, args) {
        println "M >> $name $args"
    }

    def propertyMissing(String name, args) {
        println "P >> $name"
    }
}

def clos = {
    // This call doesn't call "propertyMissing"
    String

    // This does
    Strin

    // This will call "methodMissing"
    String {
    }

    // This will not call neither methodMissing nor propertyMissing
    "STRING"

    // This will call methodMissing
    "STRING"()
}

clos.delegate = new DslEvaluator()
clos.resolveStrategy = Closure.DELEGATE_ONLY
clos()

clos compiles to

        java.lang.Object clos = { 
            java.lang.String
            Strin 
            this.String({ 
            })
            'STRING'
            this.STRING()
        }

Secondly, I am not sure what you mean by existing class

What I mean by "existing class" is a class in the current scope.

I want "hooks" when the DSL looks like...

def clos = {
   String
   Integer
   Float
}

I don't see any solution apart from an AST transformation. Your issue, here, is basically that String is a valid expression, which returns a Class, so it's like any other piece of code, it compiles and evaluates fine...