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@ -1,6 +1,6 @@
target: reference/index
template: reference
title: MoonScript v0.2.1 - Language Guide
title: MoonScript v0.2.2 - Language Guide
short_name: lang
--
MoonScript is a programming language that compiles to
@ -20,20 +20,27 @@ homepage are located at <http://moonscript.org>.
## Assignment
Unlike Lua, there is no `local` keyword. All assignments to names that are not
already defined will be declared as local to the scope of that declaration. If
you wish to create a global variable it must be done using the `export`
keyword.
Assigning to an undeclared name will cause it to be declared as a new local
variable. The language is dynamically typed so you can assign any value to any
variable. You can assign multiple names and values at once just like Lua:
```moon
hello = "world"
a,b,c = 1, 2, 3
hello = 123 -- uses the existing variable
```
If you wish to create a global variable it must be done using the
[`export`](#export) keyword.
The `local` keyword can be used to forward declare a variable, or shadow an
existing one.
## Update Assignment
`+=`, `-=`, `/=`, `*=`, `%=`, `..=` operators have been added for updating a value by
a certain amount. They are aliases for their expanded equivalents.
`+=`, `-=`, `/=`, `*=`, `%=`, `..=`, `or=`, `and=` operators have been added
for updating and assigning at the same time. They are aliases for their
expanded equivalents.
```moon
x = 0
@ -41,6 +48,9 @@ a certain amount. They are aliases for their expanded equivalents.
s = "hello "
s ..= "world"
b = false
b and= true or false
```
## Comments
@ -70,7 +80,6 @@ denoted using the arrow: `->`
my_function() -- call the empty function
```
The body of the function can either be one statement placed directly after the
arrow, or it can be a series of statements indented on the following lines:
@ -98,9 +107,9 @@ argument names in parentheses:
sum = (x, y) -> print "sum", x + y
```
Functions can be called by listing the values of the arguments after the name
of the variable where the function is stored. When chaining together function
calls, the arguments are applied to the closest function to the left.
Functions can be called by listing the arguments after the name of an expresion
that evaluates to a function. When chaining together function calls, the
arguments are applied to the closest function to the left.
```moon
sum 10, 20
@ -117,6 +126,8 @@ right arguments get sent to the right functions.
print "x:", sum(10, 20), "y:", sum(30, 40)
```
There must not be any space between the opening parenthesis and the function.
Functions will coerce the last statement in their body into a return statement,
this is called implicit return:
@ -146,7 +157,7 @@ calling a method, a special syntax is provided for creating functions which
automatically includes a `self` argument.
```moon
func = (num) => self.value + num
func = (num) => @value + num
```
### Argument Defaults
@ -188,8 +199,9 @@ the `-`. Consider the examples below.
```
The precedence of the first argument of a function call can also be controlled
using whitespace if the argument is a literal string.In Lua, it is common to
leave off parentheses when calling a function with a single string literal.
using whitespace if the argument is a literal string. In Lua, it is common to
leave off parentheses when calling a function with a single string or table
literal.
When there is no space between a variable and a string literal, the
function call takes precedence over any following expressions. No other
@ -249,7 +261,7 @@ instead of being part of the table.
```
Although uncommon, notice how we can give a deeper indentation for function
arguments if we know we will be using a lower indentation futher on.
arguments if we know we will be using a lower indentation further on.
```moon
y = { my_func 1,2,3,
@ -348,7 +360,7 @@ same as the variable names, then the `:` prefix operator can be used:
If you want the key of a field in the table to to be result of an expression,
then you can wrap it in `[` `]`, just like in Lua. You can also use a string
literal directly as a key, leaving out the square brackets. This is useful if
your key has any special chacters.
your key has any special characters.
```moon
t = {
@ -360,12 +372,12 @@ your key has any special chacters.
## Comprehensions
Compiling provide a convenient syntax for constructing a new table by iterating
over some existing object and applying an expression to its values. There are
two kinds of comprehensions: list comprehensions and table comprehensions. They
both produce Lua tables; _list comprehensions_ accumulate values into an
array-like table, and _table comprehensions_ let you set both the key and the
value on each iteration.
Comprehensions provide a convenient syntax for constructing a new table by
iterating over some existing object and applying an expression to its values.
There are two kinds of comprehensions: list comprehensions and table
comprehensions. They both produce Lua tables; _list comprehensions_ accumulate
values into an array-like table, and _table comprehensions_ let you set both
the key and the value on each iteration.
### List Comprehensions
@ -405,10 +417,10 @@ Using multiple `for` clauses is the same as using nested loops:
### Table Comprehensions
The syntax for table comprehensions is very similar, differing by using `{` and
The syntax for table comprehensions is very similar, only differing by using `{` and
`}` and taking two values from each iteration.
This example copies the key-value table `thing`:
This example makes a copy of the table`thing`:
```moon
thing = {
@ -477,6 +489,15 @@ size and leave the other bounds blank. This takes all odd indexed items: (1, 3,
slice = [item for item in *items[,,2]]
```
## String Interpolation
You can mix expressions into string literals using `#{}` syntax.
```moon
print "I am #{math.random! * 100}% sure."
```
String interpolation is only available in double quoted strings.
## For Loop
There are two for loop forms, just like in Lua. A numeric one and a generic one:
@ -510,7 +531,7 @@ single line:
A for loop can also be used an expression. The last statement in the body of
the for loop is coerced into an expression and appended to an accumulating
table if the value of that expression is not nil.
table if the value of that expression is not `nil`.
Doubling every even number:
@ -531,7 +552,7 @@ Filtering out odd numbers:
```
For loops at the end of a function body are not accumulated into a table for a
return value (Instead the function will return `nil`). Either an explicit
return value (Instead the function will return `nil`). Either an explicit
`return` statement can be used, or the loop can be converted into a list
comprehension.
@ -563,6 +584,27 @@ Like for loops, the while loop can also be used an expression. Additionally,
for a function to return the accumulated value of a while loop, the statement
must be explicitly returned.
## Continue
A `continue` statement can be used to skip the current iteration in a loop.
```moon
i = 0
while i < 10
continue if i % 2 ==0
print i
```
`continue` can also be used with loop expressions to prevent that iteration
from accumulating into the result. This examples filters the array table into
just even numbers:
```moon
my_numbers = {1,2,3,4,5,6}
odds = for x in *my_numbers
continue if x % 2 == 1
x
```
## Conditionals
```moon
@ -611,7 +653,7 @@ assigned variable is only in scope for the body of the conditional, meaning it
is never available if the value is not truthy.
```moon
if user = database\find_user "moon"
if user = database.find_user "moon"
print user.name
```
@ -727,7 +769,7 @@ functions, but for other types of objects, undesired results may occur.
Consider the example below, the `clothes` property is shared amongst all
instances, so modifications to it in one instance will show up in another:
```moon
```moononly
class Person
clothes: {}
give_item: (name) =>
@ -746,7 +788,7 @@ instances, so modifications to it in one instance will show up in another:
The proper way to avoid this problem is to create the mutable state of the
object in the constructor:
```moon
```moononly
class Person
new: =>
@clothes = {}
@ -767,19 +809,23 @@ properties and methods from another class.
Here we extend our Inventory class, and limit the amount of items it can carry.
In this example, we don't define a constructor on the subclass, so the parent
class' constructor is called when we make a new instance. If we did define a
constructor then we can use the [`super`](#super) method to call the parent
constructor.
Whenever a class inherits from another, it sends a message to the parent class
by calling the method `__inherited` on the parent class if it exists. The
function recieves two arguments, the class that is being inherited and the
by calling the method `__inherited` on the parent class if it exists. The
function receives two arguments, the class that is being inherited and the
child class.
```moon
```moononly
class Shelf
@__inherited: (child) =>
print @__name, "was inherited by", child.__name
-- will print: Shelf was inherited by Cupboard
class Cupboard extends Shelf
nil
```
### Super
@ -874,7 +920,7 @@ If the class extends from anything, the parent class object is stored in
We can create variables directly in the class object instead of in the *base*
by using `@` in the front of the property name in a class declaration.
```moon
```moononly
class Things
@some_func: => print "Hello from", @__name
@ -888,7 +934,7 @@ by using `@` in the front of the property name in a class declaration.
In expressions, we can use `@@` to access a value that is stored in the
`__class` of `self`. Thus, `@@hello` is shorthand for `self.__class.hello`.
```moon
```moononly
class Counter
@count: 0
@ -924,6 +970,20 @@ described above:
These expressions are executed after all the properties have been added to the
*base*.
All variables declared in the body of the class are local to the classes
properties. This is convenient for placing private values or helper functions
that only the class methods can access:
```moononly
class MoreThings
secret = 123
log = (msg) -> print "LOG:", msg
some_method: =>
log "hello world: " .. secret
```
### `@` and `@@` Values
@ -933,17 +993,54 @@ that name accessed in `self` and `self.__class`.
If they are used all by themselves, they are aliases for `self` and
`self.__class`.
```moon
assert @ == self
assert @@ == self.__class
```
For example, a quick way to create a new instance of the same class from an
instance method using `@@`:
```moon
some_instance_method = (...) => @@ ...
```
### Class Expressions
The `class` syntax can also be used as an expression which can be assigned to a
variable or explicitly returned.
```moononly
x = class Bucket
drops: 0
add_drop: => @drops += 1
```
### Anonymous classes
The name can be left out when declaring a class. The `__name` attribute will be
`nil`, unless the class expression is in an assignment. The name on the left
hand side of the assignment is used instead of `nil`.
```moononly
BigBucket = class extends Bucket
add_drop: => @drops += 10
assert Bucket.__name == "BigBucket"
```
You can even leave off the body, meaning you can write a blank anonymous class
like this:
```moononly
x = class
```
## Export Statement
Because, by default, all assignments to variables that are not lexically visible will
Because all assignments to variables that are not lexically visible will
be declared as local, special syntax is required to declare a variable globally.
The export keyword makes it so any following assignments to the specified names
@ -954,7 +1051,6 @@ will not be assigned locally.
var_name, var_name3 = "hello", "world"
```
This is especially useful when declaring what will be externally visible in a
module:
@ -986,6 +1082,9 @@ variables directly:
Additionally, a class declaration can be prefixed with the export keyword in
order to export it.
Export will have no effect if there is already a local variable of the same
name in scope.
### Export All & Export Proper
The `export` statement can also take special symbols `*` and `^`.
@ -1067,6 +1166,51 @@ Or...
me = create_person "Leaf", {dad, mother, sister}
```
In this usage, `with` can be seen as a special form of the K combinator.
The expression in the `with` statement can also be an assignment, if you want
to give a name to the expression.
```moon
with str = "Hello"
print "original:", str
print "upper:", \upper!
```
## Do
When used as a statement, `do` works just like it does in Lua.
```moon
do
var = "hello"
print var
print var -- nil here
```
MoonScript's `do` can also be used an expression . Allowing you to combine
multiple lines into one. The result of the `do` expression is the last
statement in its body.
```moon
counter = do
i = 0
->
i += 1
i
print counter!
print counter!
```
```moon
tbl = {
key: do
print "assigning key!"
1234
}
```
## Function Stubs
@ -1162,6 +1306,33 @@ accessed, they just cant be modified:
print i,k -- these have been updated
```
## Misc.
### Implicit Returns on Files
By default, a file will also implicitly return like a function. This is useful
for writing modules, where you can put your module's table as the last
statement in the file so it is returned when loaded with `require`.
### Writing Modules
Lua 5.2 has removed the `module` function for creating modules. It is
recommended to return a table instead when defining a module.
The `with` statement along with implicit return on a file provides a convenient
way to do this:
```moonret
-- my_library.moon
with _M = {}
.SOME_CONSTANT = 100
.some_function = -> print .SOME_CONSTANT
```
# MoonScript API
## `moonscript` Module
@ -1192,30 +1363,67 @@ The `moonloader`, when finding a valid path to a `.moon` file, will parse and
compile the file in memory. The code is then turned into a function using the
built in `load` function, which is run as the module.
### Load Functions
MoonScript provides `moonscript.load`, `moonscript.loadfile`,
`mooonscript.loadstring`, which are analogous to Lua's `load`, `loadfile`, and
`loadstring`.
The MoonScript functions work the same as their counterparts, except they deal
with MoonScript code instead of Lua Code.
```moononly
require "moonscript"
fn = moonscript.loadstring 'print "hi!"'
fn!
```
All of these functions can take an optional last argument, a table of options.
The only option right now is `implicitly_return_root`. Setting this to `false`
makes it so the file does not implicitly return its last statement.
```moononly
require "moonscript"
fn = moonscript.loadstring "10"
print fn! -- prints "10"
fn = moonscript.loadstring "10", implicitly_return_root: false
print fn! -- prints nothing
```
## Error Rewriting
Runtime errors are given special attention when using the `moonloader`.
Because we start off as MoonScript, but run code as Lua, errors that happen
during runtime report their line numbers as they are in the compiled file. This
can make debugging particularly difficult.
Runtime errors are given special attention when running code using the `moon`
binary. Because we start off as MoonScript, but run code as Lua, errors that
happen during runtime report their line numbers as they are in the compiled
file. This can make debugging particularly difficult.
Consider the following file with a bug:
Consider the following file with a bug (note the invalid `z` variable):
```moon
add_numbers = (x,y) -> x + z
print add_numbers 10,0
add_numbers = (x,y) -> x + z -- 1
print add_numbers 10,0 -- 2
```
The following error is generated:
moon:err.moon:1: attempt to perform arithmetic on global 'z' (a nil value)
moon: scrap.moon:1(3): attempt to perform arithmetic on global 'z' (a nil value)
stack traceback:
err.moon:1: in function 'add_numbers'
err.moon:2: in main chunk
scrap.moon:1(3): in function 'add_numbers'
scrap.moon:2(5): in main chunk
Instead of the error being reported on line number 3, where it appears in the
Lua file, it is reported on line 1, where the faulty line originated. The
entire stack trace is rewritten in addition to the error.
Notice how next to the file name there are two numbers. The first number is the
rewritten line number. The number in the parentheses is the original Lua line
number.
The error in this example is being reported on line 1 of the `moon` file, which
corresponds to line 3 of the generated Lua code. The entire stack trace is rewritten in
addition to the error message.
## Programmatically Compiling
@ -1228,7 +1436,7 @@ Lua code from MoonScript code.
Here is a quick example of how you would compile a MoonScript string to a Lua
String:
```moon
```moononly
require "moonscript.parse"
require "moonscript.compile"
@ -1294,9 +1502,9 @@ for all MoonScript files and compile them.
`moonc` can write to standard out by passing the `-p` flag.
Combined with `linotify` on linux, the `-w` flag can be used to watch all files
that match the given search path for changes, and then compile them only when
required.
The `-w` flag can be used to enable watch mode. `moonc` will stay running, and
watch for changes to the input files. If any of them change then they will be
compiled automatically.
A full list of flags can be seen by passing the `-h` or `--help` flag.

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docs/standard_lib.md
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@ -1,6 +1,6 @@
target: reference/standard_lib
template: reference
title: MoonScript v0.2.1 - Standard Library
title: MoonScript v0.2.2 - Standard Library
short_name: stdlib
--