Language Primer =============== If you know Python, you already know 99% of Codon. The following primer assumes some familiarity with Python or at least one "modern" programming language (QBASIC doesn't count). Printing -------- .. code:: python print('hello world') from sys import stderr print('hello world', end='', file=stderr) Comments -------- .. code:: python # Codon comments start with "# 'and go until the end of the line """ There are no multi-line comments. You can (ab)use the docstring operator (''') if you really need them. """ Literals -------- Codon is a strongly typed language like C++, Java, or C#. That means each expression must have a type that can be inferred at the compile-time. .. code:: python # Booleans True # type: bool False # Numbers a = 1 # type: int. It's 64-bit signed integer. b = 1.12 # type: float. Codon's float is identical to C's double. c = 5u # type: int, but unsigned d = Int[8](12) # 8-bit signed integer; you can go all the way to Int[2048] e = UInt[8](200) # 8-bit unsigned integer f = byte(3) # a byte is C's char; equivalent to Int[8] h = 0x12AF # hexadecimal integers are also welcome h = 0XAF12 g = 3.11e+9 # scientific notation is also supported g = .223 # and this is also float g = .11E-1 # and this as well # Strings s = 'hello! "^_^" ' # type: str. t = "hello there! \t \\ '^_^' " # \t is a tab character; \\ stands for \ raw = r"hello\n" # raw strings do not escape slashes; this would print "hello\n" fstr = f"a is {a + 1}" # an F-string; prints "a is 2" fstr = f"hi! {a+1=}" # an F-string; prints "hi! a+1=2" t = """ hello! multiline string """ # The following escape sequences are supported: # \\, \', \", \a, \b, \f, \n, \r, \t, \v, # \xHHH (HHH is hex code), \OOO (OOO is octal code) Tuples ~~~~~~ .. code:: python # Tuples t = (1, 2.3, 'hi') # type: Tuple[int, float, str]. t[1] # type: float u = (1, ) # type: Tuple[int] As all types must be known at compile time, tuple indexing works only if a tuple is homogenous (all types are the same) or if the value of the index is known at compile-time. You can, however, iterate over heterogenous tuples in Codon. This is achieved by unrolling the loop to accommodate the different types. .. code:: python t = (1, 2.3, 'hi') t[1] # works because 1 is a constant int x = int(argv[1]) t[x] # compile error: x is not known at compile time # This is a homogenous tuple (all member types are the same) u = (1, 2, 3) # type: Tuple[int, int, int]. u[x] # works because tuple members share the same type regardless of x for i in u: # works print(i) # Also works v = (42, 'x', 3.14) for i in v: print(i) .. note:: Tuples are **immutable**. ``a = (1, 2); a[1] = 1`` will not compile. Containers ~~~~~~~~~~ .. code:: python l = [1, 2, 3] # type: List[int]; a list of integers s = {1.1, 3.3, 2.2, 3.3} # type: Set[float]; a set of floats d = {1: 'hi', 2: 'ola', 3: 'zdravo'} # type: Dict[int, str]; a simple dictionary ln = [] # an empty list whose type is inferred based on usage ln = List[int]() # an empty list with explicit element types dn = {} # an empty dict whose type is inferred based on usage dn = Dict[int, float]() # an empty dictionary with explicit element types Because Codon is strongly typed, these won't compile: .. code:: python l = [1, 's'] # is it a List[int] or List[str]? you cannot mix-and-match types d = {1: 'hi'} d[2] = 3 # d is a Dict[int, str]; the assigned value must be a str t = (1, 2.2) # Tuple[int, float] lt = list(t) # compile error: t is not homogenous lp = [1, 2.1, 3, 5] # compile error: Codon will not automatically cast a float to an int This will work, though: .. code:: python u = (1, 2, 3) lu = list(u) # works: u is homogenous .. note:: Dictionaries and sets are unordered and are based on `klib `__. .. _operators: Assignments and operators ------------------------- .. code:: python a = 1 + 2 # this is 3 a = (1).__add__(2) # you can use a function call instead of an operator; this is also 3 a = int.__add__(1, 2) # this is equivalent to the previous line b = 5 / 2.0 # this is 2.5 c = 5 // 2 # this is 2; // is an integer division a *= 2 # a is now 6 This is the list of binary operators and their magic methods: ======== ================ ================================================== Operator Magic method Description ======== ================ ================================================== ``+`` ``__add__`` addition ``-`` ``__sub__`` subtraction ``*`` ``__mul__`` multiplication ``/`` ``__truediv__`` float (true) division ``//`` ``__floordiv__`` integer (floor) division ``**`` ``__pow__`` exponentiation ``%`` ``__mod__`` modulo ``@`` ``__matmul__`` matrix multiplication; ``&`` ``__and__`` bitwise and ``|`` ``__or__`` bitwise or ``^`` ``__xor__`` bitwise xor ``<<`` ``__lshift__`` left bit shift ``>>`` ``__rshift__`` right bit shift ``<`` ``__lt__`` less than ``<=`` ``__le__`` less or equal than ``>`` ``__gt__`` greater than ``>=`` ``__ge__`` greater or equal than ``==`` ``__eq__`` equal to ``!=`` ``__ne__`` not equal to ``in`` ``__contains__`` belongs to ``and`` none boolean and (short-circuits) ``or`` none boolean or (short-circuits) ======== ================ ================================================== Codon also has the following unary operators: ======== ================ ============================= Operator Magic method Description ======== ================ ============================= ``~`` ``__invert__`` bitwise inversion; reverse complement; ``Optional[T]`` unpacking ``+`` ``__pos__`` unary positive ``-`` ``__neg__`` unary negation ``not`` none boolean negation ======== ================ ============================= Tuple unpacking ~~~~~~~~~~~~~~~ Codon supports most of Python's tuple unpacking syntax: .. code:: python x, y = 1, 2 # x is 1, y is 2 (x, (y, z)) = 1, (2, 3) # x is 1, y is 2, z is 3 [x, (y, z)] = (1, [2, 3]) # x is 1, y is 2, z is 3 l = range(1, 8) # l is [1, 2, 3, 4, 5, 6, 7] a, b, *mid, c = l # a is 1, b is 2, mid is [3, 4, 5, 6], c is 7 a, *end = l # a is 1, end is [2, 3, 4, 5, 6, 7] *beg, c = l # c is 7, beg is [1, 2, 3, 4, 5, 6] (*x, ) = range(3) # x is [0, 1, 2] *x = range(3) # error: this does not work *sth, a, b = (1, 2, 3, 4) # sth is (1, 2), a is 3, b is 4 *sth, a, b = (1.1, 2, 3.3, 4) # error: this only works on homogenous tuples for now (x, y), *pff, z = [1, 2], 'this' print(x, y, pff, z) # x is 1, y is 2, pff is an empty tuple --- () ---, and z is "this" s, *q = 'XYZ' # works on strings as well; s is "X" and q is "YZ" Control flow ------------ Conditionals ~~~~~~~~~~~~ Codon supports the standard Python conditional syntax: .. code:: python if a or b or some_cond(): print(1) elif whatever() or 1 < a <= b < c < 4: # chained comparisons are supported print('meh...') else: print('lo and behold!') if x: y() a = b if sth() else c # ternary conditional operator Codon extends the Python conditional syntax with a ``match`` statement, which is inspired by Rust's: .. code:: python match a + some_heavy_expr(): # assuming that the type of this expression is int case 1: # is it 1? print('hi') case 2 ... 10: # is it 2, 3, 4, 5, 6, 7, 8, 9 or 10? print('wow!') case _: # "default" case print('meh...') match bool_expr(): # now it's a bool expression case True: ... case False: ... match str_expr(): # now it's a str expression case 'abc': print("it's ABC time!") case 'def' | 'ghi': # you can chain multiple rules with the "|" operator print("it's not ABC time!") case s if len(s) > 10: print("so looong!") # conditional match expression case _: assert False match some_tuple: # assuming type of some_tuple is Tuple[int, int] case (1, 2): ... case (a, _) if a == 42: # you can do away with useless terms with an underscore print('hitchhiker!') case (a, 50 ... 100) | (10 ... 20, b): # you can nest match expressions print('complex!') match list_foo(): case []: # [] matches an empty list ... case [1, 2, 3]: # make sure that list_foo() returns List[int] though! ... case [1, 2, ..., 5]: # matches any list that starts with 1 and 2 and ends with 5 ... case [..., 6] | [6, ...]: # matches a list that starts or ends with 6 ... case [..., w] if w < 0: # matches a list that ends with a negative integer ... case [...]: # any other list ... You can mix, match and chain match rules as long as the match type matches the expression type. Loops ~~~~~ Standard fare: .. code:: python a = 10 while a > 0: # prints even numbers from 9 to 1 a -= 1 if a % 2 == 1: continue print(a) for i in range(10): # prints numbers from 0 to 7, inclusive print(i) if i > 6: break ``for`` construct can iterate over any generator, which means any object that implements the ``__iter__`` magic method. In practice, generators, lists, sets, dictionaries, homogenous tuples, ranges, and many more types implement this method, so you don't need to worry. If you need to implement one yourself, just keep in mind that ``__iter__`` is a generator and not a function. Comprehensions ~~~~~~~~~~~~~~ Technically, comprehensions are not statements (they are expressions). Comprehensions are a nifty, Pythonic way to create collections: .. code:: python l = [i for i in range(5)] # type: List[int]; l is [0, 1, 2, 3, 4] l = [i for i in range(15) if i % 2 == 1 if i > 10] # type: List[int]; l is [11, 13] l = [i * j for i in range(5) for j in range(5) if i == j] # l is [0, 1, 4, 9, 16] s = {abs(i - j) for i in range(5) for j in range(5)} # s is {0, 1, 2, 3, 4} d = {i: f'item {i+1}' for i in range(3)} # d is {0: "item 1", 1: "item 2", 2: "item 3"} You can also use collections to create generators (more about them later on): .. code:: python g = (i for i in range(10)) print(list(g)) # prints number from 0 to 9, inclusive Exception handling ~~~~~~~~~~~~~~~~~~ Again, if you know how to do this in Python, you know how to do it in Codon: .. code:: python def throwable(): raise ValueError("doom and gloom") try: throwable() except ValueError as e: print("we caught the exception") except: print("ouch, we're in deep trouble") finally: print("whatever, it's done") .. note:: Right now, Codon cannot catch multiple exceptions in one statement. Thus ``catch (Exc1, Exc2, Exc3) as var`` will not compile. If you have an object that implements ``__enter__`` and ``__exit__`` methods to manage its lifetime (say, a ``File``), you can use a ``with`` statement to make your life easy: .. code:: python with open('foo.txt') as f, open('foo_copy.txt', 'w') as fo: for l in f: fo.write(l) Variables and scoping --------------------- You have probably noticed by now that blocks in Codon are defined by their indentation level (as in Python). We recommend using 2 or 4 spaces to indent blocks. Do not mix indentation levels, and do not mix tabs and spaces; stick to any *consistent* way of indenting your code. One of the major differences between Codon and Python lies in variable scoping rules. Codon variables cannot *leak* to outer blocks. Every variable is accessible only within its own block (after the variable is defined, of course), and within any block that is nested within the variable's own block. That means that the following Pythonic pattern won't compile: .. code:: python if cond(): x = 1 else: x = 2 print(x) # x is defined separately in if/else blocks; it is not accessible here! for i in range(10): ... print(i) # error: i is only accessible within the for loop block In Codon, you can rewrite that as: .. code:: python x = 2 if cond(): x = 1 # or even better x = 1 if cond() else 2 print(x) Another important difference between Codon and Python is that, in Codon, variables cannot change types. So this won't compile: .. code:: python a = 's' a = 1 # error: expected string, but got int A note about function scoping: functions cannot modify variables that are not defined within the function block. You need to use ``global`` to modify such variables: .. code:: python g = 5 def foo(): print(g) foo() # works, prints 5 def foo2(): g += 2 # error: cannot access g print(g) def foo3(): global g g += 2 print(g) foo3() # works, prints 7 foo3() # works, prints 9 As a rule, use ``global`` whenever you need to access variables that are not defined within the function. Imports ------- You can import functions and classes from another Codon module by doing: .. code:: python # Create foo.codon with a bunch of useful methods import foo foo.useful1() p = foo.FooType() # Create bar.codon with a bunch of useful methods from bar import x, y x(y) from bar import z as bar_z bar_z() ``import foo`` looks for ``foo.codon`` or ``foo/__init__.codon`` in the current directory. Functions --------- Functions are defined as follows: .. code:: python def foo(a, b, c): return a + b + c print(foo(1, 2, 3)) # prints 6 How about procedures? Well, don't return anything meaningful: .. code:: python def proc(a, b): print(a, 'followed by', b) proc(1, 's') def proc2(a, b): if a == 5: return print(a, 'followed by', b) proc2(1, 's') proc2(5, 's') # this prints nothing Codon is a strongly-typed language, so you can restrict argument and return types: .. code:: python def fn(a: int, b: float): return a + b # this works because int implements __add__(float) fn(1, 2.2) # 3.2 fn(1.1, 2) # error: 1.1. is not an int def fn2(a: int, b): return a - b fn2(1, 2) # -1 fn2(1, 1.1) # -0.1; works because int implements __sub__(float) fn2(1, 's') # error: there is no int.__sub__(str)! def fn3(a, b) -> int: return a + b fn3(1, 2) # works, as 1 + 2 is integer fn3('s', 'u') # error: 's'+'u' returns 'su' which is str, # but the signature indicates that it must return int Default arguments? Named arguments? You bet: .. code:: python def foo(a, b: int, c: float = 1.0, d: str = 'hi'): print(a, b, c, d) foo(1, 2) # prints "1 2 1 hi" foo(1, d='foo', b=1) # prints "1 1 1 foo" How about optional arguments? We support that too: .. code:: python # type of b promoted to Optional[int] def foo(a, b: int = None): print(a, b + 1) foo(1, 2) # prints "1 3" foo(1) # raises ValueError, since b is None Generics ~~~~~~~~ As we've said several times: Codon is a strongly typed language. As such, it is not as flexible as Python when it comes to types (e.g. you can't have lists with elements of different types). However, Codon tries to mimic Python's *"I don't care about types until I do"* attitude as much as possible by utilizing a technique known as *monomorphization*. If there is a function that has an argument without a type definition, Codon will consider it a *generic* function, and will generate different functions for each invocation of that generic function: .. code:: python def foo(x): print(x) # print relies on typeof(x).__str__(x) method to print the representation of x foo(1) # Codon automatically generates foo(x: int) and calls int.__str__ when needed foo('s') # Codon automatically generates foo(x: str) and calls str.__str__ when needed foo([1, 2]) # Codon automatically generates foo(x: List[int]) and calls List[int].__str__ when needed But what if you need to mix type definitions and generic types? Say, your function can take a list of *anything*? Well, you can use generic specifiers: .. code:: python def foo(x: List[T], T: type): print(x) foo([1, 2]) # prints [1, 2] foo(['s', 'u']) # prints [s, u] foo(5) # error: 5 is not a list! foo(['s', 'u'], int) # fails: T is int, so foo expects List[int] but it got List[str] def foo(x, R: type) -> R: print(x) return 1 foo(4, int) # prints 4, returns 1 foo(4, str) # error: return type is str, but foo returns int! .. note:: Coming from C++? ``foo(x: List[T], T: type): ...`` is roughly the same as ``template U foo(T x) { ... }``. Generators ~~~~~~~~~~ Codon supports generators, and they are fast! Really, really fast! .. code:: python def gen(i): while i < 10: yield i i += 1 print(list(gen(0))) # prints [0, 1, ..., 9] print(list(gen(10))) # prints [] You can also use ``yield`` to implement coroutines: ``yield`` suspends the function, while ``(yield)`` (yes, parentheses are required) receives a value, as in Python. .. code:: python def mysum[T](start: T): m = start while True: a = (yield) # receives the input of coroutine.send() call if a == -1: break # exits the coroutine m += a yield m iadder = mysum(0) # assign a coroutine next(iadder) # activate it for i in range(10): iadder.send(i) # send a value to coroutine print(iadder.send(-1)) # prints 45 .. _interop: Foreign function interface (FFI) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Codon can easily call functions from C and Python. Let's import some C functions: .. code:: python from C import pow(float, float) -> float pow(2.0, 2.0) # 4.0 # Import and rename function from C import puts(cobj) -> void as print_line # type cobj is C's pointer (void*, char*, etc.) print_line("hi!".c_str()) # prints "hi!". # Note .c_str() at the end of string--- needed to cast Codon's string to char*. ``from C import`` only works if the symbol is available to the program. If you are running your programs via ``codon``, you can link dynamic libraries by running ``codon run -l path/to/dynamic/library.so ...``. Hate linking? You can also use dyld library loading as follows: .. code:: python LIBRARY = "mycoollib.so" from C import LIBRARY.mymethod(int, float) -> cobj from C import LIBRARY.myothermethod(int, float) -> cobj as my2 foo = mymethod(1, 2.2) foo2 = my2(4, 3.2) .. note:: When importing external non-Codon functions, you must explicitly specify argument and return types. How about Python? If you have set the ``CODON_PYTHON`` environment variable as described in the first section, you can do: .. code:: python from python import mymodule.myfunction(str) -> int as foo print(foo("bar")) Often you want to execute more complex Python code within Codon. To that end, you can use Codon's ``@python`` annotation: .. code:: python @python def scipy_here_i_come(i: List[List[float]]) -> List[float]: # Code within this block is executed by the Python interpreter, # and as such it must be valid Python code import scipy.linalg import numpy as np data = np.array(i) eigenvalues, _ = scipy.linalg.eig(data) return list(eigenvalues) print(scipy_here_i_come([[1.0, 2.0], [3.0, 4.0]])) # [-0.372281, 5.37228] with some warnings... Codon will automatically bridge any object that implements the ``__to_py__`` and ``__from_py__`` magic methods. All standard Codon types already implement these methods. Classes and types ----------------- Of course, Codon supports classes! However, you must declare class members and their types in the preamble of each class (like you would do with Python's dataclasses). .. code:: python class Foo: x: int y: int def __init__(self, x: int, y: int): # constructor self.x, self.y = x, y def method(self): print(self.x, self.y) f = Foo(1, 2) f.method() # prints "1 2" .. note:: Codon does not (yet!) support inheritance and polymorphism. Unlike Python, Codon supports method overloading: .. code:: python class Foo: x: int y: int def __init__(self, x: int, y: int): # constructor self.x, self.y = 0, 0 def __init__(self, x: int, y: int): # another constructor self.x, self.y = x, y def __init__(self, x: int, y: float): # another constructor self.x, self.y = x, int(y) def __init__(self): self.x, self.y = 0, 0 def method(self: Foo): print(self.x, self.y) Foo().method() # prints "0 0" Foo(1, 2).method() # prints "1 2" Foo(1, 2.3).method() # prints "1 2" Foo(1.1, 2.3).method() # error: there is no Foo.__init__(float, float) Classes can also be generic: .. code:: python class Container[T]: l: List[T] def __init__(self, l: List[T]): self.l = l ... Classes create objects that are passed by reference: .. code:: python class Point: x: int y: int ... p = Point(1, 2) q = p # this is a reference! p.x = 2 print((p.x, p.y), (q.x, q.y)) # (2, 2), (2, 2) If you need to copy an object's contents, implement the ``__copy__`` magic method and use ``q = copy(p)`` instead. Codon also supports pass-by-value types via the ``@tuple`` annotation: .. code:: python @tuple class Point: x: int y: int p = Point(1, 2) q = p # this is a copy! print((p.x, p.y), (q.x, q.y)) # (1, 2), (1, 2) However, **by-value objects are immutable!**. The following code will not compile: .. code:: python p = Point(1, 2) p.x = 2 # error! immutable type Under the hood, types are basically named tuples (equivalent to Python's ``collections.namedtuple``). You can also add methods to types: .. code:: python @tuple class Point: x: int y: int def __new__(): # types are constructed via __new__, not __init__ return Point(0, 1) # and __new__ returns a tuple representation of type's members def some_method(self): return self.x + self.y p = Point() # p is (0, 1) print(p.some_method()) # 1 Type extensions ~~~~~~~~~~~~~~~ Suppose you have a class that lacks a method or an operator that might be really useful. Codon provides an ``@extend`` annotation that allows programmers to add and modify methods of various types at compile time, including built-in types like ``int`` or ``str``. This actually allows much of the functionality of built-in types to be implemented in Codon as type extensions in the standard library. .. code:: python class Foo: ... f = Foo(...) # We need foo.cool() but it does not exist... not a problem for Codon @extend class Foo: def cool(self: Foo): ... f.cool() # works! # How about we add support for adding integers and strings: @extend class int: def __add__(self: int, other: str): return self + int(other) print(5 + '4') # 9 Note that all type extensions are performed strictly at compile time and incur no runtime overhead. Magic methods ~~~~~~~~~~~~~ Here is a list of useful magic methods that you might want to add and overload: ================ ============================================= Magic method Description ================ ============================================= operators overload unary and binary operators (see :ref:`operators`) ``__copy__`` copy-constructor for ``copy`` method ``__len__`` for ``len`` method ``__bool__`` for ``bool`` method and condition checking ``__getitem__`` overload ``obj[key]`` ``__setitem__`` overload ``obj[key] = value`` ``__delitem__`` overload ``del obj[key]`` ``__iter__`` support iterating over the object ``__str__`` support printing and ``str`` method ================ ============================================= Other types ~~~~~~~~~~~ Codon provides arbitrary-width signed and unsigned integers, e.g. ``Int[32]`` is a signed 32-bit integer while ``UInt[128]`` is an unsigned 128-bit integer, respectively (note that ``int`` is an ``Int[64]``). Typedefs for common bit widths are provided in the standard library, such as ``i8``, ``i16``, ``u32``, ``u64`` etc. The ``Ptr[T]`` type in Codon also corresponds to a raw C pointer (e.g. ``Ptr[byte]`` is equivalent to ``char*`` in C). The ``Array[T]`` type represents a fixed-length array (essentially a pointer with a length). Codon also provides ``__ptr__`` for obtaining a pointer to a variable (as in ``__ptr__(myvar)``) and ``__array__`` for declaring stack-allocated arrays (as in ``__array__[int](10)``). LLVM functions ~~~~~~~~~~~~~~ In certain cases, you might want to use LLVM features that are not directly accessible with Codon. This can be done with the ``@llvm`` attribute: .. code:: python @llvm def llvm_add[T](a: T, b: T) -> T: %res = add {=T} %a, %b ret {=T} %res print(llvm_add(3, 4)) # 7 print(llvm_add(i8(5), i8(6))) # 11 -------------- Issues, feedback, or comments regarding this tutorial? Let us know `on GitHub `__.