Carp borrows its looks from Clojure but the runtime semantics are much closer to those of ML or Rust.
Types are inferred but can be annotated for readability using the the keyword (see below).
Memory management is handled by static analysis, a value is owned by the function where it was created.
When a value is returned or passed to another function the initial function will give up ownership of it
and any subsequent use will lead to a compiler error. To temporarily lend a value to another function
(for example to print it) a reference must be created, using the ref special form (or the & reader macro).
To learn more about the details of memory management, check out Memory.md
;; Comments begin with a semicolon and continue until the end of the line.
100 ;; Int
1500l ;; Long
3.14f ;; Float
10.0 ;; Double
1b ;; Byte
true ;; Bool
"hello" ;; &String
#"hello" ;; &Pattern
\e ;; Char
[1 2 3] ;; (Array Int)
{1 1.0 2 2.0} ;; (Map Int Double)
t ;; Type variables begin with a lowercase letter
(f t) ;; Type constructor variables; matches `(Maybe Int)` but not `Int`
Int
Long
Float
Double
Byte
Bool
String
Pattern
Char
(Array t)
(Map <key-type> <value-type>)
(Fn [<arg-type1> <arg-type2> ...] <return-type>) ;; Function type
Right now the following data types are only available for manipulation in non-compiled code.
(1 2 3) ; list
foo ; symbol
(defn function-name [<arg1> <arg2> ...] <body>) ;; Define a function (will be compiled, can't be called at the REPL)
(definterface interface-name (Fn [<t1> <t2>] <return>)) ;; Define a generic function that can have multiple implementations
(def variable-name value) ;; Define a global variable (only handles primitive constants for the moment)
(defmacro <name> [<arg1> <arg2> ...] <macro-body>) ;; Define a macro, its argument will not be evaluated when called
(defdynamic <name> <value>) ;; A variable that can only be used at the REPL or during compilation
(defndynamic <name> [<arg1> <arg2> ...] <function-body>) ;; A function that can only be used at the REPL or during compilation
(defmodule <name> <definition1> <definition2> ...) ;; The main way to organize your program into smaller parts
condThe cond statement executes a block of code if a specified condition is true. If the condition is false, another block of code can be executed.
(doc cond "this is the documentation for cond")
Usage:
(cond
(<condition_1>) (<code_1>) ;; code_1 gets executed if condition_1 is true
(<condition_2>) (<code_2>) ;; code_2 gets executed if condition_2 is true
(<code_3>) ;; code_3 gets executed if condition_1 and condition_2 are false
Here’s an example about printing a statement depending on whether it is < or > 10:
(cond
(< 10 1) (println "Don't print!")
(> 10 1) (println msg)
(println "Don't print!"))
The following forms can be used in Carp source code and will be compiled to C after type checking and other static analysis. The first three of them are also available in dynamic functions.
(fn [<arg1> <arg2> ...] <body>) ;; Create a lambda function (a.k.a. closure)
(let [<var1> <expr1> <var2> <expr2> ...] <body>) ;; Create local bindings
(do <expr1> <expr2> ... <return-expression>) ;; Perform side-effecting functions, then return a value
(if <expression> <true-branch> <false-branch>) ;; Branching
(while <expression> <body>) ;; Loop until expression is false
(use <module>) ;; Brings all symbols inside <module> into the scope
(with <module> <expr1> <expr2> ...) ;; Locally scoped `use` statement where all expressions after it will look up symbols in the <module>
(match <expression> <case1> <expr1> <case2> <expr2> ...) ;; Pattern matches an <expression> against a set of sumtype constructors
(match-ref <expression> <case1> <expr1> <case2> <expr2> ...) ;; Pattern matches an <expression> of reference type, not taking ownership of its members
(ref <expression>) ;; Borrow an owned value
(set! <variable> <expression>) ;; Mutate a variable
(the <type> <expression>) ;; Explicitly declare the type of an expression
Here’s an example of how to use the the form to make an identity function that only accepts Integers:
(defn f [x]
(the Int x))
&x ;; same as (ref x)
@x ;; same as (copy x)
When using a statically typed language like Carp it can sometimes be hard to know what value should be used at a specific point in your program. In such cases the concept of ‘holes’ can be useful. Just add a hole in your source code and reload (“:r”) to let the Carp compiler figure out what type goes there.
(String.append ?w00t "!") ;; Will generate a type error telling you that the type of '?w00t' is &String
(quote <expression>) ;; Avoid further evaluation of the expression
(and) (or) (not) ;; Logical operators
These can only be used at the REPL and during macro evaluation. Here’s a subset with some of the most commonly used ones:
(car <collection>) ;; Return the first element of a list or array
(cdr <collection>) ;; Return all but the first element of a list or array
(cons <expr> <list>) ;; Add the value of <expr> as the first element the <list>
(cons-last <expr> <list>) ;; Add the value of <expr> as the last element the <list>
(list <expr1> <expr2> ...) ;; Create a list from a series of evaluated expressions
(array <expr1> <expr2> ...) ;; Create an array from a series of evaluated expressions
To see all functions available in the Dynamic module, enter (info Dynamic) at the REPL.
Any structure type defined in Carp has an init method that can be used to create a new instance. It must be called with all the arguments in the order they are defined.
(deftype Vector2 [x Int, y Int])
(let [my-pos (Vector2.init 10 20)]
...)
;; Additionally, a 'lens' is automatically generated for each member; signatures for reference:
;; Vector2.x (Fn [(Ref Vector2)] (Ref Int))
(Vector2.x &my-pos) ;; => 10
;; Vector2.set-x (Fn [Vector2 Int] Vector2)
(Vector2.set-x my-pos 30) ;; => (Vector2 30 20)
;; Vector2.set-x! (Fn [(Ref Vector2), Int] ())
(Vector2.set-x! &my-pos 30) ;; => Will update the vector my-pos in place and return ()
;; Note the inner reference to a function
;; Vector2.update-x (Fn [Vector2, (Ref (Fn [Int] Int))] Vector2)
(Vector2.update-x my-pos inc) ;; => (Vector2 11 20)
;; This can also be a lambda
(Vector2.update-x my-pos &(fn [n] (* n 3))) ;; => (Vector2 30 20)
There are two ways to define sumtypes:
Enumeration:
(deftype MyEnum
Kind1
Kind2
Kind3)
Data:
(deftype (Either a b)
(Left [a])
(Right [b]))
A Variant can be created with the same syntax as call expression:
(MyEnum.Kind1)
(Either.Left 10)
(Either.Right 11)
;; Or use `use` statement
(use Either)
(Left 10)
(Right 11)
(use MyEnum)
(Kind1)
(Kind2)
(Kind3)
You can use pattern matching to extract values in a safe way:
(defn get [either]
(match either
(Either.Left a) a
(Either.Right b) b))
(with MyEnum
;; You can give a generic "otherwise" statement as well
(match myenum
(Kind1) (logic1)
_ (logic-other)))
Note that match works with values (not references) takes ownership over the value being matched on. If you instead want to match on a reference, you can use match-ref:
(match-ref &might-be-a-string
(Just s) (IO.println s)
Nothing (IO.println "Got nothing"))
Note that this code would not take ownership over might-be-a-string. Also, the s in the first case is a reference, since it wouldn’t be safe to destructure the Maybe into values in this situation.
Note: A sumtype cannot have more than 128 inhabitants, also known as constructors. If that reads to you like a byte limitation, you’re on the right track. While this is a limitation, it has not proved to be a problem as of yet.
Functions and variables can be stored in modules which are named and can be nested. To use a symbol inside a module
you need to qualify it with the module name, like this: Float.cos.
Using a module makes it possible to access its members without qualifying them:
(use Float)
(defn f []
(cos 3.2f))
If there are several used modules that contain symbols with the same name, the type inferer will try to figure
out which one of the symbols you really mean (based on the types in your code). If it can’t, it will display an error.
For example, both the module String and Array contain a function named ‘length’. In the following code it’s
possible to see that it’s the array version that is needed, and that one will be called:
(use String)
(use Array)
(defn f []
(length [1 2 3 4 5]))
In the following example it’s not possible to figure out which type is intended:
(use String)
(use Array)
(defn f [x]
(length x))
Specifying the type solves this error:
(use String)
(use Array)
(defn f [x]
(String.length x))
When you use a module, its declarations are brought into the current scope. If you use a module in the global scope, all of its declarations are brought into global scope after the call to use. Similarly, if you use a module in another module’s scope, its declarations can be referred to without qualifiers within the scope of the module:
(use String)
;; Only the `String` module is used in the global scope,
;; so we can refer to `length` without a module qualifier.
(defn f [x]
(length x))
(defmodule Foo
(use Array)
;; Since the the `String` module is used in the global scope,
;; and the Foo module `use`s `Array`, we again need to qualify calls to `length`
;; to disambiguate which declaration we're referring to.
(defn g [xs]
(Array.length xs)))
Sometimes, it’s more convenient to bring a module’s declarations into scope only for a limited number of forms. You can do this using the with form:
(defmodule Foo
;; we need to use a module qualifier here,
;; since there's no call to `use` in the `Foo` module scope.
(defn f [x]
(String.length x))
;; Using the `with` form, we can reference the module's declarations
;; unqualified in all the forms contained in the `with`'s scope.
(with String
(defn g [x]
(length x))))
It can be useful to keep some bindings internal to a module, to achieve that
one can use private and hidden:
(defmodule Say
; Makes `hell` inaccessible outside of module `Say`
(private hell)
; Will prevent `hell` from being visible when listing bindings in `Say`
(hidden hell)
(defn hell [] @"hell")
; `private` & `hidden` work with `def` and `defn`
(private o)
(hidden o)
(def o @"o")
; Can access `hell` and `o` inside the module
(defn hello [] (String.concat &[(hell) @&o])))
; Valid call as `hello` is not private
(Say.hello)
; Will result in an compile time error as `hell` is private to the `Say` module
(Say.hell)
defn- and def- can be used as a shorthand for defining a binding and
marking it as private & hidden, the following example is equivalent to the
previous one:
(defmodule Say
(defn- hell [] @"hell")
(def- o @"o")
(defn hello [] (String.concat &[(hell) @&o])))
Interfaces specify a generic function signature that multiple concrete
functions may implement. You can define an interface using
definterface, passing a name and type signature of a function:
(definterface speak (Fn [a] String))
You can declare a function as an implementation of an interface using
implements. For example, the following snippet declares Dog.bark
and Cat.meow as an implementation of speak:
(definterface speak (Fn [a] String))
(defmodule Dog
(defn bark [aggressive?]
(if aggressive? @"WOOF!" @"woof!"))
(implements speak Dog.bark))
(defmodule Cat
(defn meow [times] (String.repeat times "meow!"))
(implements speak Cat.meow))
Only functions that satisfy an interface’s signature can implement
it. For exmaple, the following function isn’t a valid implementation
of speak because it has the wrong number of arguments and its return
type does not match the return type of speak:
(defmodule Number
;; who knew numbers could talk?
(defn holler [] "WOO!")
(implements speak Number.holler))
=> [INTERFACE ERROR] Number.holler : (Fn [] (Ref String a)) doesn't match the interface signature (Fn [a] String)
When you call an interface by name, Carp uses the current context and the type signature of each implementation to call an implementation that type checks:
(speak 2) ;; Int -> String, Cat.meow
=> "meow!meow!"
(speak false) ;; Bool -> String, Dog.bark
=> "woof!"
If more than one interface implementation satisfies Carp’s type checker in a given context, Carp will complain about the ambiguity:
(defmodule Pikachu
(defn pika [times] (String.repeat times "pika!"))
(implements speak Pikachu.pika))
(speak 2) ;; Int -> String, Cat.meow OR Pikachu.pika
=> There are several exact matches for the interface `speak` of type `(Fn [Int] String)` at line 1, column 2 in 'REPL'
Possibilities:
Cat.meow : (Fn [Int] String)
Pikachu.pika : (Fn [Int] String) at REPL:1:1.
In such cases, you’ll have to help the Carp compiler disambiguate the call by calling the implementing function you need directly. It usually isn’t useful to provide multiple implementations that have the same function signature.
(system-include "math.h") ;; compiles to #include <math.h>
(relative-include "math.h") ;; compiles to #include "$carp_file_dir/math.h" where carp_file_dir is the absolute path to the folder containing the invoking .carp file
(register blah (Fn [Int Int] String)) ;; Will register the function 'blah' that takes two Int:s and returns a String
(register pi Double) ;; Will register the global variable 'pi' of type Double
(register blah (Fn [Int Int] String) "exit") ;; Will register the function 'blah' but use the name 'exit' in the emitted C code.
(register-type Apple) ;; Register an opaque C type
(register-type Banana [price Double, size Int]) ;; Register an external C-struct, this will generate getters, setters and updaters.
Often type names in C are lowercase (e.g. size_t) and just registering them will be problematic since Carp thinks that such variables are generic types.
To be able to interop wich such types, register-type takes an optional string after the type name, like this:
(register-type SizeT "size_t")
This will make the name of the type in Carp code be SizeT, while the emitted C code will use size_t instead.
More information on C interop…
Patterns are similar to, but not the same as, Regular Expressions. They were derived from Lua, and are useful whenever you want to find something within or extract something from strings.
They are simpler than Regular Expressions, as they do not provide alternation. Nonetheless, they are often very useful and, because they are simpler, also faster and more predictable.
Here is a little overview of the API:
; you can initialize a pattern with a literal or create one from a string
#"[a-z]"
(Pattern.init "[a-z]")
; you can also get a string back from it
(str #"[a-z]")
(prn #"[a-z]")
; you can find things in strings by index
(Pattern.find #"[a-z]" "1234a") ; => 4
(Pattern.find #"[a-z]" "1234") ; => -1
; also multiple things at once!
(Pattern.find-all #"[a-z]" "1234a b") ; => [4 6]
; matches? checks whether a string matches a pattern
(Pattern.matches? #"(\d+) (\d+)" " 12 13") ; => true
; match-groups returns all match groups of the first match
(Pattern.match-groups #"(\d+) (\d+)" " 12 13") ; => ["12" "13"]
; match-str returns the whole string of the first match
(Pattern.match-str #"(\d+) (\d+)" " 12 13") ; => "12 13"
; global-match gets all match groups of all matches
(Pattern.global-match #"(\d+) (\d+)" " 12 13 14 15") ; => [["12" "13"] ["14" "15"]]
; substitute helps you replace patterns in a string n times
(Pattern.substitute #"sub-me" "sub-me sub-me sub-me" "replaced" 1) ; => "replaced sub-me sub-me"
; if you want to replace every occurrence, use -1
(Pattern.substitute #"sub-me" "sub-me sub-me sub-me" "replaced" -1) ; => "replaced replaced replaced"
As mentioned above, patterns are not as expressive as regular expressions. The fundamental difference is that patterns do not backtrack. This means that they cannot express alternation (because we can’t go back to where we branched) and we cannot reduce non-greedy matches on the left. The latter point might not be obvious, so let us look at an example:
(Pattern.match-all-groups #"1.-2" "1 1 2") ; => [[@"1 1 2"]]
A valid, less greedy match would have been "1 2", but since it would have
required us to go back to the left after we had started matching to reduce the
match size, this is not done. As such, while - is similar to *? in regular
expressions, it is not the same. Often, a more explicit variant of the pattern
can be found that is able to resolve the issues (in the case above, #"1\s-2"
might have been desirable, for instance).