[ballerina/en] Add Ballerina Programming Language (#4085)

* Add Ballerina programming language

* Update Ballerina language code with objects and transactions information

* Fix code formatting

* Update code

* Fix code formatting

1 files changed, 432 insertions, 0 deletions

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+---
+language: Ballerina
+contributors:
+    - ["Anjana Fernando", "https://github.com/lafernando"]
+filename: learn_ballerina.bal
+---
+
+[Ballerina](https://ballerina.io/) is a statically-typed programming language for making development for the cloud an enjoyable experience. 
+
+```ballerina
+// Single-line comment
+
+// Import modules into the current source file 
+import ballerina/io;
+import ballerina/time;
+import ballerina/http;
+import ballerinax/java.jdbc;
+import ballerina/lang.'int as ints;
+import ballerinax/awslambda;
+// Module alias "af" used in code in place of the full module name
+import ballerinax/azure.functions as af;
+
+http:Client clientEP = new ("https://freegeoip.app/");
+jdbc:Client accountsDB = new ({url: "jdbc:mysql://localhost:3306/AccountsDB", 
+                               username: "test", password: "test"});
+
+// A service is a first-class concept in Ballerina, and is one of the 
+// entrypoints to a Ballerina program. 
+// The Ballerina platform also provides support for easy deployment to 
+// environments such as Kubernetes (https://ballerina.io/learn/deployment/kubernetes/).
+service geoservice on new http:Listener(8080) {
+
+    @http:ResourceConfig {
+        path: "/geoip/{ip}"
+    }
+    resource function geoip(http:Caller caller, http:Request request,
+                            string ip) returns @tainted error? {
+        http:Response resp = check clientEP->get("/json/" + <@untainted>ip);
+        check caller->respond(<@untainted> check resp.getTextPayload());
+    }
+
+}
+
+// Serverless Function-as-a-Service support with AWS Lambda.
+// The Ballerina compiler automatically generates the final deployment 
+// artifact to be deployed.
+@awslambda:Function
+public function echo(awslambda:Context ctx, json input) returns json {
+    return input;
+}
+
+@awslambda:Function
+public function notifyS3(awslambda:Context ctx, 
+                         awslambda:S3Event event) returns json {
+    return event.Records[0].s3.'object.key;
+}
+
+// Serverless Function-as-a-Service support with Azure Functions.
+// Similar to AWS Lambda, the compiler generates the deployment artifacts.
+@af:Function
+public function fromQueueToQueue(af:Context ctx, 
+        @af:QueueTrigger { queueName: "queue1" } string inMsg,
+        @af:QueueOutput { queueName: "queue2" } af:StringOutputBinding outMsg) {
+    outMsg.value = inMsg;
+}
+
+// A custom record type
+public type Person record {
+    string id;              // required field
+    string name;            
+    int age?;               // optional field
+    string country = "N/A"; // default value
+};
+
+@af:Function
+public function fromHttpTriggerCosmosDBInput(
+        @af:HTTPTrigger { route: "c1/{country}" } af:HTTPRequest httpReq, 
+        @af:CosmosDBInput { connectionStringSetting: "CosmosDBConnection", 
+        databaseName: "db1", collectionName: "c1", 
+        sqlQuery: "select * from c1 where c1.country = {country}" } 
+        Person[] dbReq)
+        returns @af:HTTPOutput string|error {
+    return dbReq.toString();
+}
+
+public function main() returns @tainted error? {
+    int a = 10;               // 64-bit signed integer
+    float b = 1.56;           // 64-bit IEEE 754-2008 binary floating point number
+    string c = "hello";       // a unicode string
+    boolean d = true;         // true, false
+    decimal e = 15.335;       // decimal floating point number
+
+    var f = 20;               // type inference with 'var' - 'f' is an int
+    
+    int[] intArray = [1, 2, 3, 4, 5, 6];
+    int x = intArray.shift(); // similar to a dequeue operation
+    x = intArray.pop();       // removes the last element
+    intArray.push(10);        // add to the end
+
+    // Tuples - similar to a fixed length array with a distinct type for each slot
+    [string, int] p1 = ["Jack", 1990]; 
+    [string, int] p2 = ["Tom", 1986];
+    io:println("Name: ", p1[0], " Birth Year: ", p1[1]);
+
+    string name1;
+    int birthYear1;
+    [name1, birthYear1] = p1;     // tuple destructuring
+
+    var [name2, birthYear2] = p2; // declare and assign values in the same statement
+
+    // If statements
+    int ix = 10;
+    if ix < 10 {
+        io:println("value is less than 10");
+    } else if ix == 10 {
+        io:println("value equals to 10");
+    } else {
+        io:println("value is greater than 10");
+    }
+
+    // Loops
+    int count = 10;
+    int i = 0;
+    while i < 10 {
+        io:println(i);
+    }
+    // Loop from 0 to count (inclusive)
+    foreach var j in 0...count {
+        io:println(j);
+    }
+    // Loop from 0 to count (non-inclusive)
+    foreach var j in 0..<count {
+        io:println(j);
+    }
+    // Loop a list
+    foreach var j in intArray {
+        io:println(j);
+    }
+
+    json j1 = { "name" : name1, "birthYear" : birthYear1, "zipcode" : 90210 };
+    io:println(j1.name, " - ", j1.zipcode);
+    // New fields are added to a JSON value through "mergeJson"
+    var j2 = j1.mergeJson({ "id" : "90400593053"});
+
+    // XML namespace declaration
+    xmlns "http://example.com/ns1" as ns1;
+    xmlns "http://example.com/default";
+    
+    // XML variable from a literal value
+    xml x1 = xml `<ns1:entry><name>{{name1}}</name><birthYear>{{birthYear1}}</birthYear></ns1:entry>`;
+    io:println(x1);
+    // Access specific elements in the XML value
+    io:println(x1/<name>);
+    // List all child items in the XML value
+    io:println(x1/*);
+
+    // Function invocations
+    x = add(1, 2);
+    io:println(multiply(2, 4));
+    // Invocation providing value for the defaultable parameter
+    io:println(multiply(3, 4, true));
+    // Invocation with values to a rest parameter (multi-valued)
+    io:println(addAll(1, 2, 3));
+    io:println(addAll(1, 2, 3, 4, 5));
+
+    // Function pointers
+    (function (int, int) returns int) op1 = getOperation("add");
+    (function (int, int) returns int) op2 = getOperation("mod");
+    io:println(op1(5, 10));
+    io:println(op2(13, 10));
+
+    // Closures
+    (function (int x) returns int) add5 = getAdder(5);
+    (function (int x) returns int) add10 = getAdder(10);
+    io:println(add5(10));
+    io:println(add10(10));
+
+    int[] numbers = [1, 2, 3, 4, 5, 6, 7, 8];
+    // Functional iteration
+    int[] evenNumbers = numbers.filter(function (int x) returns boolean { return x % 2 == 0; });
+
+    // Union types - "input" is of type either string or byte[]
+    string|byte[] uval = "XXX";
+
+    // A type test expression ("uval is string") can be used to check the 
+    // runtime type of a variable.
+    if uval is string {
+        // In the current scope, "uval" is a string value
+        string data = "data:" + uval;
+    } else {
+        // Since the expression in the "if" statement ruled out that it's not a string,
+        // the only type left is "byte[]"; so in the current scope, "uval" will always
+        // be a "byte[]".
+        int inputLength = uval.length();
+    }
+
+    // Error handling
+    string input = io:readln("Enter number: ");
+    int|error result = ints:fromString(input);
+    if result is int {
+        io:println("Number: ", result);
+    } else {
+        io:println("Invalid number: ", input);
+    }
+
+    // A check expression can be used to directly return the error from
+    // the current function if its subexpression evaluated to an error
+    // value in the runtime. 
+    int number = check ints:fromString(input); 
+
+    // Concurrent execution using workers in a function
+    doWorkers();
+
+    // Asynchronous execution with futures
+    future<int> f10 = start fib(10);
+    var webresult = clientEP->get("/");
+    int fresult = wait f10;
+    if webresult is http:Response {
+        io:println(webresult.getTextPayload());
+        io:println(fresult);
+    }
+
+    // Mapping types
+    map<int> ageMap = {};
+    ageMap["Peter"] = 25;
+    ageMap["John"] = 30;
+
+    int? agePeter = ageMap["Peter"]; // int? is the union type int|() - int or nill
+    if agePeter is int {
+        io:println("Peter's age is ", agePeter);
+    } else {
+        io:println("Peter's age is not found");
+    }
+
+    Person person1 = { id: "p1", name : "Anne", age: 28, country: "Sri Lanka" };
+    Scores score1 = { physics : 80, mathematics: 95 };
+    score1["chemistry"] = 75;
+    io:println(score1["chemistry"]);
+
+    Student student1 = { id: "s1", name: "Jack", age: 25, country: "Japan" };
+    student1.college = "Stanford";
+    string? jacksCollege = student1?.college; // optional field access
+    if jacksCollege is string {
+        io:println("Jack's college is ", jacksCollege);
+    }
+
+    // Due to the structural type system, "student1" can be assigned to "person2",
+    // since the student1's structure is compatible with person2's,
+    // where we can say, a "Student" is a "Person" as well. 
+    Person person2 = student1;
+
+    map<int> grades = {"Jack": 95, "Anne": 90, "John": 80, "Bill": 55};
+    Person px1 = {id: "px1", name: "Jack", age: 30, country: "Canada"};
+    Person px2 = {id: "px2", name: "John", age: 25};
+    Person px3 = {id: "px3", name: "Anne", age: 17, country: "UK"};
+    Person px4 = {id: "px4", name: "Bill", age: 15, country: "USA"};
+    Person[] persons = [];
+    persons.push(px1);
+    persons.push(px2);
+    persons.push(px3);
+    persons.push(px4);
+
+    // Query expressions used to execute complex queries for list data
+    Result[] results = from var person in persons
+                       let int lgrade = (grades[person.name] ?: 0)
+                       where lgrade > 75 
+                           let string targetCollege = "Stanford"
+                           select { 
+                               name: person.name, 
+                               college: targetCollege, 
+                               grade: lgrade 
+                           };
+
+    // Compile-time taint checking for handling untrusted data
+    string s1 = "abc";
+    mySecureFunction(s1);
+    // Explicitely make "s2" a tainted value. External input to a Ballerina
+    // program such as command-line arguments and network input are by-default
+    // marked as tainted data.
+    string s2 = <@tainted> s1;
+    // "s2x" is now a tainted value, since its value is derived using a 
+    // tainted value (s1).
+    string s2x = s2 + "abc";
+    // The following line uncommented will result in a compilation error,
+    // since we are passing a tainted value (s2x) to a function which 
+    // exepects an untainted value.
+    // mySecureFunction(s2x);
+
+    // Instantiating objects
+    Employee emp1 = new("E0001", "Jack Smith", "Sales", 2009);
+    io:println("The company service duration of ", emp1.name, 
+               " is ", emp1.serviceDuration());
+
+    // Supported operations can be executed in a transaction by enclosing the actions
+    // in a "transaction" block. 
+    transaction {
+        // Executes the below database operations in a single local transactions
+        var r1 = accountsDB->update("UPDATE Employee SET balance = balance + ? WHERE id = ?", 5500.0, "ID001");
+        var r2 = accountsDB->update("UPDATE Employee SET balance = balance + ? WHERE id = ?", 5500.0, "ID001");
+    }
+}
+
+// An object is a behavioural type, which encapsulates both data and functionality.
+type Employee object {
+    
+    // Private fields are only visible within the object and its methods
+    private string empId;
+    // Public fields can be accessed by anyone
+    public string name;
+    public string department;
+    // The default qualifier is a "protected" field, 
+    // which are accessible only within the module.
+    int yearJoined;           
+    
+    // The object initialization function; automatically called when an object is instantiated.
+    public function __init(string empId, string name, string department, int yearJoined) {
+        self.empId = empId;
+        self.name = name;
+        self.department = department;
+        self.yearJoined = yearJoined;        
+    }
+
+    // An object method
+    public function serviceDuration() returns int {
+        time:Time ct = time:currentTime();
+        return time:getYear(ct) - self.yearJoined;
+    }
+
+};
+
+// Student is a subtype of Person
+type Student record {
+    string id;
+    string name;
+    int age;
+    string college?;
+    string country;
+};
+
+type Scores record {
+    int physics;
+    int mathematics;
+};
+
+type Result record {
+    string name;
+    string college;
+    int grade;
+};
+
+public function getOperation(string op) returns (function (int, int) returns int) {
+    if op == "add" {
+        return add;
+    } else if op == "mod" {
+        return function (int a, int b) returns int { // anonymous function
+            return a % b;
+        };
+    } else {
+        return (x, y) => 0; // single expression anonymous no-op function 
+    }
+}
+
+// Two required parameters
+public function add(int a, int b) returns int {
+    return a + b;
+}
+
+// 'log' is a defaultable parameter
+public function multiply(int a, int b, boolean log = false) returns int {
+    if log {
+        io:println("Multiplying ", a, " with ", b);
+    }
+    return a * b;
+}
+
+// 'numbers' is a rest parameter - it can have multiple values, 
+// similar to an array.
+public function addAll(int... numbers) returns int {
+    int result = 0;
+    foreach int number in numbers {
+        result += number;
+    }
+    return result;
+}
+
+public function getAdder(int n) returns (function (int x) returns int) {
+    return function (int x) returns int { // returns closure
+        return x + n;
+    };
+}
+
+function fib(int n) returns int {
+    if n <= 2 {
+        return 1;
+    } else {
+        return fib(n - 1) + fib(n - 2);
+    }
+}
+
+// The code in worker blocks "w1" and "w2" are executed concurrency 
+// when this function is invoked. The "wait" expressions waits for
+// the given workers to finish to retrieve their results.
+public function doWorkers() {
+    worker w1 returns int {
+        int j = 10;
+        j -> w2;
+        int b;
+        b = <- w2;
+        return b * b;
+    }
+    worker w2 returns int {
+        int a;
+        a = <- w1;
+        a * 2 -> w1;
+        return a + 2;
+    }
+    record {int w1; int w2;} x = wait {w1, w2};
+    io:println(x);
+}
+
+// A function which takes in only an untainted string value.
+public function mySecureFunction(@untainted string input) {
+    io:println(input);
+}
+```
+
+### Further Reading
+
+* [Ballerina by Example](https://ballerina.io/learn/by-example/)
+* [User Guide](https://ballerina.io/learn/installing-ballerina/)
+* [API Documentation](https://ballerina.io/learn/api-docs/ballerina/)
+* [Language Specification](https://ballerina.io/spec/)