demo.rhm

#lang rhombus

// we'll define macros much later, but by convention,
// `import` goes at the top:
import:
  rhombus/meta open
// alternatively, use `#lang rhombus/and_meta`

// to ensure that we're not sloppy in examples:
use_static
// alternatively, use `#lang rhombus/static`

// ------------------------------------------------------------
"Basics: expressions, variables, and functions"

// some expressions

10 * (-3) + 2
10 + (-3) * 2

#false || !(#false || #false && #true)

// `++` is append on strings
"hello" ++ " " ++ "world"

// `+&` turns things into strings, then appends
"example: " +& (0 + 1) +& " world "

// Lists

[1, 2, 3]
List.cons(0, [1, 2, 3])
[0, & [1, 2, 3]]

// `++` is append on lists
[1, 2, 3] ++ [4, 5]

// a definition
def π = 3.14
π

// a pattern-matching definition
// `_` matches without binding anything
def [ca, _] = List.cons(1, List.cons(2, List.empty))
ca

// parentheses around a pattern do not matter
def (((ππ))) = π * π
ππ

// comma-separated patterns in parentheses match multiple values
def (_, mb, _):
  values("1", "2", "3")
mb

// or use `values`, if you prefer
def values(_, also_mb, _):
  values("1", "2", "3")
also_mb

// define and call a function
// function arguments are also pattern-matched
fun five(_):
  5

five("anything")
3*five(#true && #false || 2 < 3) - 2

// `fun` without a name is an expression that produces a function, so
// you could also define a function like this:
def identity = fun (x): x

identity("hello")
identity(1 + (fun (x): x)(99))

// a shorthand notation with wildcard is also available, parenthesized
def identity_short = (_)

identity_short("it works!")
identity_short(1 + (_)(42))

// this notation is especially useful in pipelines
"pipe it" |> identity_short(_)

// `|>` binds weaker than other operators
// cryptic way to write (1 - 2) + 1, not 1 - (2 + 1)
1 - 2 |> (_ + 1)

// ------------------------------------------------------------
"Conditionals"

// plain old `if`
if 1 == 2
| "oops"
| "sensible"

// multi-arm `if`
cond
| 1 == 3: "oops"
| 1 == 2: "also oops"
| 1 == 1: "sensible"
| ~else: "shouldn't get here"

// pattern-matching dispatch
match [1, 2]
| [_, _, _]: "oops"
| [x, y]: [y, x]
| ~else: "shouldn't get here, either"

// ------------------------------------------------------------
"More functions"

// keyword and optional arguments

// a keyword starts `~`, and a keyword argument is written
// as a keyword followed by `:`, while an optional argument
// is one that has a default supplied via `=`

fun six(_, ~plus: amt = 0):
  6 + amt
six("anything")
six("anything", ~plus: 7)

fun seven(x, ~plus: amt = x, y = amt):
  7 + amt - y

seven(12)
seven("anything", ~plus: 13)
seven(12, 10)
seven(12, 10, ~plus: 8)

// pattern-matching on a function argument

fun first_one([x, _]): x

first_one(["alpha", "beta"])

// would be an error, since a string doesn't match the pattern:
//  first_one("oops")

// a `::` constrains a match to a data type
fun also_first_one(x :: List): List.first(x)

also_first_one([1, 2, 3, 4])
// would be an error, since a string doesn't match:
//  also_first_one("oops")

// a function result annotation is written before the body `:`

fun add1(x) :: Int:
  match x
  | _ :: Int : x + 1
  | ~else: x

add1(100)
// would trigger an error, since "oops" is not an `Int`:
//  add1("oops")

fun
| add_two(x) :: Number:
    x + 2.0
| add_two(x, y) :: String:
    x +& " and " +& y

add_two(7) .= 9.0
add_two(6, 7) == "6 and 7"

// ------------------------------------------------------------
"Defining operators"

// defining an infix operator

operator (a +* b):
  (a + b) * b

3 +* 4

operator (x mod y):
  x - math.floor(x / y) * y

10 mod 3

// with precedence and associativity

operator (a ++* b):
  ~weaker_than: *
  ~associativity: ~right
  (a + b) * b

3 ++* 4 * 2 ++* 5
3 ++* ((4 * 2) ++* 5)

// defining a prefix operator

operator (!! b):
  ! ! b

!!#true

// defining an operator that is both prefix and infix

operator
| (** exponent):
    2 ** exponent
| (base ** exponent):
    if exponent == 0
    | 1
    | base * (base ** (exponent-1))

3 ** 8
** 10 // = 2 ** 10

// ------------------------------------------------------------
"Lists, arrays, maps, sets, and repetitions"

def nums = [1, 2, 3]
def yes_nums :: List = nums
def yep_nums :: List.of(Int) = nums

// `[]` on a list accesses by a 0-based index
nums[1]

block:
  // `use_dynamic` because `also_nums` is not declared to be a list
  use_dynamic
  def also_nums = if #true | nums | #false
  also_nums[1]

def nums_a = Array(1, 2, 3)
def yes_nums_a :: Array: nums_a
// `now_of` checks immediately
def yep_nums_a :: Array.now_of(Int): nums_a

// unlike lists, arrays are mutable and support assignment with `:=`
nums_a[1]
nums_a[2] := 30
nums_a[2]

// `later_of` doesn't check immediately, but checks on read/write
def really_nums_a :: Array.later_of(Int): nums_a
really_nums_a[1]
really_nums_a[2] := 42
really_nums_a[2]
// writing non-`Int` would fail
//  really_nums_a[2] := "oops"

// the `Map` constructor expects `key: value` pairs in `{}`
def map = Map{17: "hello", 24: "goodbye"}
def yes_map :: Map = map
def yup_map :: Map.of(Int, String) = map

map

// `[]` on a map find the value for a key
map[17]

// `Map` is also bound as a constructor function, in which case
// it expects 2-argument lists for the keys and values
def also_map = Map([1, "one"], [2, "two"])
also_map[2]

// `Map` is the default constructor triggered by `{}`
def also_also_map = {1: "one", 2: "two"}
also_also_map[2]

// a symbol is something like a string, often used for efficient map access
def key_map = {#'a: "ay", #'b: "bee"}
key_map[#'a]

// a map can have different kinds of keys
def mixed_map = {#'a: 1, "b": 2}
mixed_map[#'a] + mixed_map["b"]

// a mutable map supports update via `:=`
def mut_map = MutableMap{1: "mone"}
mut_map[1]
mut_map[2] := "mtwo"
mut_map[2]

// using `{}` without `:` creates a set instead of a map
def a_set = {1, 3, 5, 7, 9}

// `[]` on a set checks whether something is in a set
if a_set[1] && !a_set[2]
| "ok"
| error("no way!")

// some patterns forms (like `[]`) support `...` to create a repetition
// binding, and some with constructors (like `[]`) support `...` to
// reference a repetition
def [x, y, ...] = nums
[y, ...]
[y, ..., 0, y, ...]

// when you have a list instead of a repetition, some constructors
// (like `[]`) recoginize `&` to splice elements of the list
[100, 1000, & nums]
[& nums, 0, & nums]

// in a map construction, `&` splices an existing map:
{& also_also_map, 100: "hundred"}
{100: "hundred", & also_also_map, & map }

// and so on for sets:
{& a_set, 0}

// function calls can also use `...`
block:
  fun f(a, _): a
  // this works because `y` happens to have two elements:
  f(y, ...)

// function definitions, too
fun
| slow_add(): 0
| slow_add(x, y, ...): x + slow_add(y, ...)

slow_add(1, 2, 3)

// or you can write it "rest"-argument style
fun
| also_slow_add(): 0
| also_slow_add(x, & y): x + slow_add(& y)

also_slow_add(1, 2, 3)

// it's more often useful to use `...` in function-argument list patterns:
fun
| sum([]): 0
| sum([x, y, ...]): x + sum([y, ...])

sum([1, 2, 3])

fun
| is_sorted([] || [_]): #true
| is_sorted([head, next, tail, ...]):
   head .<= next && is_sorted([next, tail, ...])

is_sorted([1, 2, 3, 4, 5])
is_sorted([1, 2, 30, 4, 5])

// ------------------------------------------------------------
"Classes as records"

class Posn(x, y)

// the class name is a constructor
Posn(1, 2)

// access a field using `.`
Posn(2, 3).x

// alternatively, `Posn.x` is an accessor function
Posn.x(Posn(2, 3))

fun md(p :: Posn):
  p.x + p.y
md(Posn(1, 4))

// here, we need `use_dynamic`, since `p` is not known to be a `Posn`;
// it can look up `x` and `y` dynamically, but `use_static` at the top
// of this module
fun md2(p):
  use_dynamic
  p.x + p.y

md2(Posn(5, 6))
block:
  // dynamic lookup means that we can pass in anything that has `x` and `y`:
  class Chromosomes(x, y, other)
  md2(Chromosomes(100, 200, 314))

// `:~` is similar to `::`, but it declares static information without a
// corresponding run-time check, so a failure may happen later if the claimed
// information is incorrect

fun md3(p :~ Posn):
  p.x + p.y
md3(Posn(7, 8))
// would trigger an error at `p.x` instead of the function call:
//  md3("oops")

// `is_a` is an expression operator that takes an annotation to check
Posn(1, 2) is_a Posn
5 is_a Posn

// `::` is an expression operator to form a run-time assertion
(Posn(1, 2) :: Posn).x
// static `.x` here would be allowed, but `::` would fail at run time:
//  (5 :: Posn).x

// function with multiple cases to match different kinds of calls
fun
| size(n :: Int):
    n
| size(p :: Posn):
    p.x + p.y
| size(a, b):
    a+b

size(Posn(8, 6))
size(1, 2)

// class names also work as binding patterns
def Posn(px, py) = Posn(1, 2)
[px, py]

// Nested class types with annotations
class IPosn(x :: Int, y :: Int)
class ILine(p1 :: IPosn, p2 :: IPosn)

IPosn(1, 2).x

// would be an error:
//  IPosn("x", "y")

def l1 = ILine(IPosn(1, 2), IPosn(3, 4))

// can statically access `x` from `p2` and similar
l1.p2.x
ILine.p1(l1).x
(l1.p1 :: IPosn).x
block:
  def ILine(p1, p2) = l1
  p1.x + p2.y

// ------------------------------------------------------------
"Classes and interfaces with methods"

interface Shape:
  method area() :: Real

class Circle(radius):
  implements Shape
  override area():
    π * radius * radius

class Rectangle(width, height):
  implements Shape
  nonfinal
  override area():
    width * height

class Square(color):
  extends Rectangle
  constructor(side):
    // curried `super` takes superclass arguments first
    super(side, side)("blue")

def s :: Shape:
  def pick = 2
  match pick
  | 0: Circle(2)
  | 1: Rectangle(3, 4)
  | 2: Square(5)

s.area()

// ------------------------------------------------------------
"Syntax objects and macros"

// single-quotes make a syntax object, not a string
'1 + 2'

// would be an error, since `1x` is not a valid identifier,
// because parentheses are not balanaced, or because a block
// would be empty
//  '1x'
//  '1)'
//  'x:'

// single quotes also work as a pattern form to match a syntax object,
// where `$` escapes to bind a match
match '1 + 2'
| '$x + $y': [x, y]

match '1 * 2'
| '$x + $y': [x, y]
| 'x * y': "matched literal x and y"
| '$x * $y': [x, y]

// `$` escapes work in quotes for creating an expression, too
match '1 + 2'
| '$x + $y': '$y + $x'

// `...` works with syntax patterns and macros
match '1 2 3'
| '$n ...': '([$n], ...)'

// when it's the only thing in a group or block, an escape variable
// can match the whole group or block:
match '([{1 + 2}])'
| '([{ $g }])': g

match '([{1 + 2, 3 + 4}])'
| '([{ $(g :: Multi) }])': g

// the `macro` form defines a simple pattern-based expression macro:
macro 'thunk: $body':
  'fun (): $body'

def delayed_area = thunk: s.area()
delayed_area()

// the `expr.macro` form defines a macro where the result is determined
// by arbitrary expand-time code
expr.macro 'find_matching_name $expr ...: $id ...':
  // convert identifiers to strings
  let [name, ...] = [to_string(id), ...]
  // build a result conditional
  'block:
     def val = $expr ...
     cond
     | val == $id: $name
     | ...'

block:
  def x = 1
  def y = 2
  def z = 3
  find_matching_name 1+1: x y z

// `defn.macro` defines a macro that can expand to definitions
defn.macro 'def_fives: $id ...':
  'def $id = 5
   ...'

def_fives: cinco wu lima
wu + lima + cinco

// would be an error, because `def_fives` is not an expression form
//  1 + def_fives

// ------------------------------------------------------------
"Potpourri"

// namespaces are like local modules

namespace Geometry:
  fun combined_areas(s1 :: Shape, s2 :: Shape):
    s1.area() + s2.area()
  export:
    combined_areas
    // can export things defined outside the namespace
    Shape Circle Square

Geometry.combined_areas(Geometry.Square(1), Geometry.Square(2))

// `let` is a definition that is only visible later

fun check_later():
  ok_later

let accum: 1
let accum: accum+1
let accum: accum+1
accum

def ok_later = "ok"
check_later()

// for

fun enumerate(l :: List):
  for (v: l,
       i: 0..):
    println(i +& ". " +& v)

enumerate(["a", "b", "c"])

fun grid(m, n):
  for List:
    each i: 0..m
    each j: 0..n
    [i, j]

grid(2, 3)

fun loop_sum(l :: List):
  for values(sum = 0) (i: l):
    sum+i

loop_sum([2, 3, 4])

// mutable variables

def mutable count = 0
count := count + 1
count