tutorial

VV’s syntax is designed to be familiar to Go developers while being a bit simpler and more streamlined.

You can test the VV code in online Playground.

Values and Value Types

In VV, everything is a value, and, all values are associated with a type.

19 + 84               // int values
"aomame" + `kawa`     // string values
-9.22 + 1e10          // float values
true || false         // bool values
'九' > '9'             // char values
[1, false, "foo"]     // array value
{a: 12.34, b: "bar"}  // map value
func() { /*...*/ }    // function value

Here’s a list of all available value types in VV.

Error Values

In VV, an error can be represented using “error” typed values. An error value is created using error expression, and, it must have an underlying value. The underlying value of an error value can be access using .value selector.

err1 := error("oops")    // error with string value
err2 := error(1+2+3)     // error with int value
if is_error(err1) {      // 'is_error' builtin function
  err_val := err1.value  // get underlying value
}  

Immutable Values

In VV, basically all values (except for array and map) are immutable.

s := "12345"
s[1] = 'b'    // illegal: String is immutable

a := [1, 2, 3]
a[1] = "two"  // ok: a is now [1, "two", 3]

An array or map value can be made immutable using immutable expression.

b := immutable([1, 2, 3])
b[1] = "foo"  // illegal: 'b' references to an immutable array.

Note that re-assigning a new value to the variable has nothing to do with the value immutability.

s := "abc"
s = "foo"                  // ok
a := immutable([1, 2, 3])
a = false                  // ok

Note that, if you copy (using copy builtin function) an immutable value, it will return a “mutable” copy. Also, immutability is not applied to the individual elements of the array or map value, unless they are explicitly made immutable.

a := immutable({b: 4, c: [1, 2, 3]})
a.b = 5        // illegal
a.c[1] = 5     // ok: because 'a.c' is not immutable

a = immutable({b: 4, c: immutable([1, 2, 3])})
a.c[1] = 5     // illegal

Undefined Values

In VV, an “undefined” value can be used to represent an unexpected or non-existing value:

• A function that does not return a value explicitly considered to return undefined value.
• Indexer or selector on composite value types may return undefined if the key or index does not exist.
• Type conversion builtin functions without a default value will return undefined if conversion fails.

a := func() { b := 4 }()    // a == undefined
b := [1, 2, 3][10]          // b == undefined
c := {a: "foo"}["b"]        // c == undefined
d := int("foo")             // d == undefined

Array Values

In VV, array is an ordered list of values of any types. Elements of an array can be accessed using indexer [].

[1, 2, 3][0]       // == 1
[1, 2, 3][2]       // == 3
[1, 2, 3][3]       // == undefined

["foo", "bar", [1, 2, 3]]   // ok: array with an array element

Map Values

In VV, map is a set of key-value pairs where key is string and the value is of any value types. Value of a map can be accessed using indexer [] or selector ‘.’ operators.

m := { a: 1, b: false, c: "foo" }
m["b"]                                // == false
m.c                                   // == "foo"
m.x                                   // == undefined

{a: [1,2,3], b: {c: "foo", d: "bar"}} // ok: map with an array element and a map element  

Function Values

In VV, function is a callable value with a number of function arguments and a return value. Just like any other values, functions can be passed into or returned from another function.

my_func := func(arg1, arg2) {
  return arg1 + arg2
}

adder := func(base) {
  return func(x) { return base + x }  // capturing 'base'
}
add5 := adder(5)
nine := add5(4)    // == 9

Unlike Go, VV does not have declarations. So the following code is illegal:

func my_func(arg1, arg2) {  // illegal
  return arg1 + arg2
}

VV also supports variadic functions/closures:

variadic := func (a, b, ...c) {
  return [a, b, c]
}
variadic(1, 2, 3, 4) // [1, 2, [3, 4]]

variadicClosure := func(a) {
  return func(b, ...c) {
    return [a, b, c]
  }
}
variadicClosure(1)(2, 3, 4) // [1, 2, [3, 4]]

Only the last parameter can be variadic. The following code is also illegal:

// illegal, because a is variadic and is not the last parameter
illegal := func(a..., b) { /*... */ }

When calling a function, the number of passing arguments must match that of function definition.

f := func(a, b) {}
f(1, 2, 3) // Runtime Error: wrong number of arguments: want=2, got=3

Like Go, you can use ellipsis ... to pass array-type value as its last parameter:

f1 := func(a, b, c) { return a + b + c }
f1([1, 2, 3]...)    // => 6
f1(1, [2, 3]...)    // => 6
f1(1, 2, [3]...)    // => 6
f1([1, 2]...)       // Runtime Error: wrong number of arguments: want=3, got=2

f2 := func(a, ...b) {}
f2(1)               // valid; a = 1, b = []
f2(1, 2)            // valid; a = 1, b = [2]
f2(1, 2, 3)         // valid; a = 1, b = [2, 3]
f2([1, 2, 3]...)    // valid; a = 1, b = [2, 3]

Variables and Scopes

A value can be assigned to a variable using assignment operator := and =.

• := operator defines a new variable in the scope and assigns a value.
• = operator assigns a new value to an existing variable in the scope.

Variables are defined either in global scope (defined outside function) or in local scope (defined inside function).

a := "foo"      // define 'a' in global scope

func() {        // function scope A
  b := 52       // define 'b' in function scope A
  
  func() {      // function scope B
    c := 19.84  // define 'c' in function scope B

    a = "bee"   // ok: assign new value to 'a' from global scope
    b = 20      // ok: assign new value to 'b' from function scope A

    b := true   // ok: define new 'b' in function scope B
                //     (shadowing 'b' from function scope A)
  }
  
  a = "bar"     // ok: assigne new value to 'a' from global scope
  b = 10        // ok: assigne new value to 'b'
  a := -100     // ok: define new 'a' in function scope A
                //     (shadowing 'a' from global scope)
  
  c = -9.1      // illegal: 'c' is not defined
  b := [1, 2]   // illegal: 'b' is already defined in the same scope
}

b = 25          // illegal: 'b' is not defined
a := {d: 2}     // illegal: 'a' is already defined in the same scope

Unlike Go, a variable can be assigned a value of different types.

a := 123        // assigned    'int'
a = "123"       // re-assigned 'string'
a = [1, 2, 3]   // re-assigned 'array'

Type Conversions

Although the type is not directly specified in VV, one can use type conversion builtin functions to convert between value types.

s1 := string(1984)    // "1984"
i2 := int("-999")     // -999
f3 := float(-51)      // -51.0
b4 := bool(1)         // true
c5 := char("X")       // 'X'

See Operators for more details on type coercions.

Operators

Unary Operators

In VV, all values can be either truthy or falsy.

Binary Operators

See Operators for more details.

Ternary Operators

VV has a ternary conditional operator (condition expression) ? (true expression) : (false expression).

a := true ? 1 : -1    // a == 1

min := func(a, b) {
  return a < b ? a : b
}
b := min(5, 10)      // b == 5

Assignment and Increment Operators

Operator Precedences

Unary operators have the highest precedence, and, ternary operator has the lowest precedence. There are five precedence levels for binary operators. Multiplication operators bind strongest, followed by addition operators, comparison operators, && (logical AND), and finally || (logical OR):

Like Go, ++ and -- operators form statements, not expressions, they fall outside the operator hierarchy.

Selector and Indexer

One can use selector (.) and indexer ([]) operators to read or write elements of composite types (array, map, string, bytes).

["one", "two", "three"][1]  // == "two"

m := {
  a: 1,
  b: [2, 3, 4],
  c: func() { return 10 }
}
m.a              // == 1
m["b"][1]        // == 3
m.c()            // == 10
m.x = 5          // add 'x' to map 'm'
m["b"][5]        // == undefined
m["b"][5].d      // == undefined
m.b[5] = 0       // == undefined
m.x.y.z          // == undefined

Like Go, one can use slice operator [:] for sequence value types such as array, string, bytes.

a := [1, 2, 3, 4, 5][1:3]    // == [2, 3]
b := [1, 2, 3, 4, 5][3:]     // == [4, 5]
c := [1, 2, 3, 4, 5][:3]     // == [1, 2, 3]
d := "hello world"[2:10]     // == "llo worl"
c := [1, 2, 3, 4, 5][-1:10]  // == [1, 2, 3, 4, 5]

Note: Keywords cannot be used as selectors.

a := {in: true} // Parse Error: expected map key, found 'in'
a.func = ""     // Parse Error: expected selector, found 'func'

Use double quotes and indexer to use keywords with maps.

a := {"in": true}
a["func"] = ""

Statements

If Statement

“If” statement is very similar to Go.

if a < 0 {
  // execute if 'a' is negative
} else if a == 0 {
  // execute if 'a' is zero
} else {
  // execute if 'a' is positive
}

Like Go, the condition expression may be preceded by a simple statement, which executes before the expression is evaluated.

if a := foo(); a < 0 {
  // execute if 'a' is negative
}

For Statement

“For” statement is very similar to Go.

// for (init); (condition); (post) {}
for a:=0; a<10; a++ {
  // ...
}

// for (condition) {}
for a < 10 {
  // ...
}

// for {}
for {
  // ...
}

For-In Statement

“For-In” statement is new in VV. It’s similar to Go’s for range statement. “For-In” statement can iterate any iterable value types (array, map, bytes, string, undefined).

for v in [1, 2, 3] {          // array: element
  // 'v' is value
}
for i, v in [1, 2, 3] {       // array: index and element
  // 'i' is index
  // 'v' is value  
}
for k, v in {k1: 1, k2: 2} {  // map: key and value
  // 'k' is key
  // 'v' is value
}

Modules

Module is the basic compilation unit in VV. A module can import another module using import expression.

Main module:

sum := import("./sum")  // load module from a local file
fmt.print(sum(10))      // module function

Another module in sum.vv file:

base := 5

export func(x) {
  return x + base
}

In VV, modules are very similar to functions.

• import expression loads the module code and execute it like a function.
• Module should return a value using export statement.
  • Module can return export a value of any types: int, map, function, etc.
  • export in a module is like return in a function: it stops execution and return a value to the importing code.
  • export-ed values are always immutable.
  • If the module does not have any export statement, import expression simply returns undefined. (Just like the function that has no return.)
  • Note that export statement is completely ignored and not evaluated if the code is executed as a main module.

Also, you can use import expression to load the Standard Library as well.

math := import("math")
a := math.abs(-19.84)  // == 19.84

Comments

Like Go, VV supports line comments (//...) and block comments (/* ... */).

/*
  multi-line block comments
*/

a := 5    // line comments

Differences from Go

Unlike Go, VV does not have the following:

• Declarations
• Imaginary values
• Structs
• Pointers
• Channels
• Goroutines
• Tuple assignment
• Variable parameters
• Switch statement
• Goto statement
• Defer statement
• Panic
• Type assertion