This chapter showcases Acorn's features using code examples and hyperlinks to the appropriate detailed documentation.
Comments
# Line comments start with a '#' and continue to end of line ### Block comments start and end with three '#' symbols in a row. They can span multiple lines. ###
Literal values: Each comment specifies the type of the values.
null # Null true, false # Bool 123, -3 # Integer 3.4, 0.3E-2 # Float 'sum' # Symbol "Χαίρετε" # Text # Text values are mutable, Text literals are not. # Text literals may use escape sequences and span multiple lines # (all control characters are stripped) "A line.\n\tIndented line\n \t\"Another line\u00BF\""
# Global variables start with a capital letter or $ Integer # Capital letter globals are used for types $, $window # $ globals hold environment values # Local and closure variables start with lower case letter, unicode value or _ balance, π, temp2, toReturn, _temp_, funny?
Assignment: Assignments may be placed within expressions.
a = 3.4 # a now holds the Integer 3.4 a,b = b,a # parallel assignment (this swaps their values) a = b = c # a and b now have the value found in c a = (b = c) + 1 # assignments may be embedded in expressions a += 1 # operator assignment, incrementing value of a
# Property names begin with a lowercase letter
child.lastname = parent.lastname # properties may be retrieved or assigned
# Method names begin with a uppercase letter or symbol
list.Sort # parameters may be omitted
list.Find('banana') # parameters may be provided
number.'+'(1) # single quotes when method name is not like a variable
(2).(op)(3) # Calculated method. Result is 6 when op='*'
frosty.Jump(10).Yell("Ow!").Grow(0.9) # Method chaining
# Shortcuts:
funccall(a) # Equivalent to self.funccall(a)
letters[5] # Index. Equivalent to letters.'[]'(5)
glyphs[4] = "π" # Uses the setter method for '[]': glyphs.'[]'("π", 4)
+List('a','b') # Creates a new list. Equivalent to: List.New('a', 'b')
+Regex"abc" # Equivalent to Regex.New("abc")
1 .. 4 # equivalent to: +Range(1,4)
# Arithmetic operators
a+b*c # equivalent to a.'+'(b.'*'(c))
Method Definition: Methods are always anonymous first-class values
# [] begins a method declaration and encloses parameter variables # undeclared parameter 'self' is always received # parameter b defines a default value: b=1 if b===null # '...' indicates variable number of additional parameters newfunc = [a, b=1, ...] # method's body is a statement block with tab-indented lines # each line's statement implicitly ends with ';' local c,d = 4,'abc' # declare and initialize local variables 'c' and 'd' a = sum(self, a, ...) # pass variable parameters on to sum method a*b, c+d.size # implicitly return two values (5).newfunc(3, 2, 5, 7) # returns 40, 7 (5 is treated as self's value) newfunc(3) # returns 10, 7 (if self is 7 when called)
Closure Definition: Closures bind their state by value
# Explicitly declared closure: +[ ] encloses closure variables # Note: explicit is only way to bind 'self' in closure (e.g., for event handling) next = +[count=0] [] count += 1 $ increment and return count next() # 1 next() # 2 # Implicitly defined closure - equivalent to above count = 0 next = [] # since 'count' is declared before method, this wraps method within a closure # 'count' is treated as a closure variable whose value is bound to 0 count += 1 # increment and return count
Get/set Closure: Useful for computed properties
# This get/set closure binds the 'count' closure variable to two methods
iter = +[count=0]
[] { count += 1; }
[v] { count = v; }
# Using the closure
iter() # 1 - uses the 'get' method
iter() # 2
iter() = 0 # reset counter to 0 - uses the 'set' method
iter() # 1 - count starts over
Yielder Definition: (methods that preserve execution state; co-routines)
fibo: *[start=1, inc=0] while true yield start start,inc = start+inc, start fiboi = fibo() # Create a new yielder iterator fiboi(), fiboi(), fiboi(), fiboi(), fiboi() # 1, 1, 2, 3, 5
Conditions and if:
# if block if needs_more? # fails when false or null, succeeds otherwise fill_it_up() elif shape==='square' # exact equivalence: same object shape = 'rectangle' elif height<5.4 # Uses '<=>' method: -1/less, 0/equal, 1/more, null/uncomparable grow() elif 5 ~~ 1 .. 7 # match operator. Equivalent to +Range(1,7).'~~'(5) "I knew that" elif a or b and not c # boolean operators "Illogical!" else default_action() # three ways to assign a default value to 'a' if it is null a = a ? a else 1 # ternary operator a = 1 if not a # if clause a = a or 1 # boolean expression
# match applies '~~' method to each 'with' value match ship.speed with 0.0 .. 1.5 ship.state = 'landing' with 1.5 .. 4.0 ship.state = 'crashing' else ship.state = 'flattened'
x = 0
while x<=10
x += 1
continue if x===3 # 'continue' goes back to start of loop
Vm.Log("DANGER, DANGER! Will Robinson")
break if x===5 # 'break' halts loop
# while clause
item = get_next() while item!='slurpy'
npcs[i] # establishes value of 'this' for following block
scene.Register(this)
.Jump(10.) # equivalent to: this.Jump(10.)
shape = .shape # equivalent to: shape = this.shape
.Grow(1.1)
# Use 'this' blocks to build multi-layered, typed content
smaug = +Dragon
name: "Smaug" # equivalent to: this::name="Smaug"
color: 'green'
loot: +List # 'this' = the new List for following block
<< 'gem' # appends 'gem' to the smaug.loot list
<< 'ring' # equivalent to: this.'<<'('ring')
# Calculate 30 using 'each' block sum = 0 each n in 1 .. 10 if n.Even? sum += n sum += n if n.Even? each n in 1 .. 10 # equivalent, using 'each' clause # 'each' iterates over collections yield item each item in list # uses list.Each to create closure iterator for list yield key,value each key:value in index vm.Log(msg) each msg in ... # iterate over variable parameters # Use 'each' with 'this' blocks to build procedural content # This creates a list of fibonacci integers from 1 to 89 (<100) fiblist = +List each n in fibo() # 'each' works with yielders/closures break if n>100 << n
Types: Prototypes, Mixins, Classes
# Create a new type derived from Character
WingedHorse = +Character
.Mixin FlyingMount # add mixin for multiple inheritance
sprite: winghorse_image # inherited property
Launch: [] # inherited method
velocity.Delta(0., 5.)
joy: +[_joy] # inherited computed property
[] {_joy}
[v] {_joy=v if v~~1 .. 5} # domain validation
# Create an instance of WingedHorse
pegasus = +WingedHorse
name: "Pegasus"
joy: 5
position: +Xy(200, 0) # Initialize starting position
.Launch # Use inherited method to launch him flying
Programs and Resources: Acorn programs are "snap-together" resources (files)
# This Acorn program's url is http://tinyurl.com/wingedhorse.acn
# A programs is a method that is run when loaded. Its return value is the value of the program.
# This program implicitly returns a new Character type (WingedHorse)
+Character
.Mixin @flyingmount # get mixin from flyingmount.acn
sprite: @images/winghorse.gif # get image from relative url
Launch: [] # inherited method
velocity.Delta(0., 5.)
joy: +[_joy] # inherited computed property
[] {_joy}
[v] {_joy=v if v~~1 .. 5} # domain validation
Another program uses the value from the above program:
# This Acorn program's url is http://tinyurl.com/pegasus.acn +@wingedhorse # use type defined in named program (above) name: "Pegasus" joy: 5 position: +Xy(200, 0) # Initialize starting position .Launch # Use inherited method to launch him flying
