dry_composition_validation.swift

    //Validate min length
    func minLength(_ value:String, min:Int, fieldName:String) -> Validation<[String], String>{
        if(value.characters.count < min){
            return Validation.Failure(["\(fieldName) must have more than \(min) characters"])
        } else {
            return Validation.Success(value)
        }
    }
    
    //Validate match a regular expression
    func matches(_ value:String, regex:String, errorMessage:String) -> Validation<[String], String>{
        if(value.range(of:regex, options: .regularExpression) == nil){
            return Validation.Failure([errorMessage])
        } else {
            return Validation.Success(value)
        }
    }
    
    //Validate password: concatenation of matches and minLength
    func isPasswordValid(_ password:String) -> Validation<[String], String> {
        return matches(password, regex: "[\\W]", errorMessage: "Password must contain an special character")
            .sconcat(minLength(password, min: 8, fieldName: "Password"))
    }
    
    //Validate name: minLength
    func isNameValid(_ name: String) -> Validation<[String], String> {
        return minLength(name, min: 3, fieldName: "Name")
    }
    
    //Validate form: concatenation of isPasswordValid and isNameValid
    func validateForm(name: String, password: String) -> Validation<[String], String> {
        return isNameValid(name)
            .sconcat(isPasswordValid(password))
    }
    
    
    //Examples
    let result = validateForm(name: "FP", password: "Ricardo$")
    /*▿ Validation<Array<String>, String>
      ▿ Failure : 1 element
        - 0 : "Name must have more than 3 characters"
    */
    let result1 = validateForm(name: "FP", password: "A")
    /*  Validation<Array<String>, String>
      ▿ Failure : 3 elements
        - 0 : "Name must have more than 3 characters"
        - 1 : "Password must contain an special character"
        - 2 : "Password must have more than 8 characters"
    */
    let result2 = validateForm(name: "FPZ", password: "A")
    /* ▿ Validation<Array<String>, String>
       ▿ Failure : 2 elements
        - 0 : "Password must contain an special character"
        - 1 : "Password must have more than 8 characters"
    */
    let result3 = validateForm(name: "FPZ", password: "A$k34k21!!")
    /* ▿ Validation<Array<String>, String>
         - Success : "A$k34k21!!"
    */