Change default ARM compiler name - Nim - This repository contains the Nim compiler, Nim's stdlib, tools, and documentation. (mirror)

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author	Michał Zieliński <michal@zielinscy.org.pl>	2018-01-21 16:26:22 +0100
committer	GitHub <noreply@github.com>	2018-01-21 16:26:22 +0100
commit	1a0f8fd4e6cf0467d77969f0105f8625fd036208 (patch)
tree	0f0e121883adf52aa538e1ab68bb75aa10b6c8b5
parent	81195fc3622bf540e783054923168371193de107 (diff)
download	Nim-1a0f8fd4e6cf0467d77969f0105f8625fd036208.tar.gz

Change default ARM compiler name

In most distros (Ubuntu, Debian, Arch Linux) the only available Linux ARM toolchain uses arm-linux-gnueabihf- prefix. That's also the correct compiler for cross-compiling code for Raspberry Pi, which is what most people will probably want.

Diffstat

-rw-r--r--

config/nim.cfg

1 files changed, 8 insertions, 3 deletions

========================= Nimrod Tutorial (Part II) ========================= :Author: Andreas Rumpf :Version: |nimrodversion| .. contents:: Introduction ============ "Object-oriented programming is an exceptionally bad idea which could only have originated in California." --Edsger Dijkstra This document is a tutorial for the advanced constructs of the *Nimrod* programming language. **Note that this document is somewhat obsolete as the `manual <manual.html>`_ contains many more examples of the advanced language features.** Pragmas ======= Pragmas are Nimrod's method to give the compiler additional information/ commands without introducing a massive number of new keywords. Pragmas are enclosed in the special ``{.`` and ``.}`` curly dot brackets. This tutorial does not cover pragmas. See the `manual <manual.html>`_ or `user guide <nimrodc.html>`_ for a description of the available pragmas. Object Oriented Programming =========================== While Nimrod's support for object oriented programming (OOP) is minimalistic, powerful OOP technics can be used. OOP is seen as *one* way to design a program, not *the only* way. Often a procedural approach leads to simpler and more efficient code. In particular, prefering composition over inheritance is often the better design. Objects ------- Like tuples, objects are a means to pack different values together in a structured way. However, objects provide many features that tuples do not: They provide inheritance and information hiding. Because objects encapsulate data, the ``()`` tuple constructor cannot be used to construct objects. So the order of the object's fields is not as important as it is for tuples. The programmer should provide a proc to initialize the object (this is called a *constructor*). Objects have access to their type at runtime. There is an ``of`` operator that can be used to check the object's type: .. code-block:: nimrod type TPerson = object of TObject name*: string # the * means that `name` is accessible from other modules age: int # no * means that the field is hidden from other modules TStudent = object of TPerson # TStudent inherits from TPerson id: int # with an id field var student: TStudent person: TPerson assert(student of TStudent) # is true Object fields that should be visible from outside the defining module have to be marked by ``*``. In contrast to tuples, different object types are never *equivalent*. New object types can only be defined within a type section. Inheritance is done with the ``object of`` syntax. Multiple inheritance is currently not supported. If an object type has no suitable ancestor, ``TObject`` can be used as its ancestor, but this is only a convention. Objects that have no ancestor are implicitely ``final``. You can use the ``inheritable`` pragma to introduce new object roots apart from ``system.TObject``. (This is used in the GTK wrapper for instance.) **Note**: Composition (*has-a* relation) is often preferable to inheritance (*is-a* relation) for simple code reuse. Since objects are value types in Nimrod, composition is as efficient as inheritance. Mutually recursive types ------------------------ Objects, tuples and references can model quite complex data structures which depend on each other; they are *mutually recursive*. In Nimrod these types can only be declared within a single type section. (Anything else would require arbitrary symbol lookahead which slows down compilation.) Example: .. code-block:: nimrod type PNode = ref TNode # a traced reference to a TNode TNode = object le, ri: PNode # left and right subtrees sym: ref TSym # leaves contain a reference to a TSym TSym = object # a symbol name: string # the symbol's name line: int # the line the symbol was declared in code: PNode # the symbol's abstract syntax tree Type conversions ---------------- Nimrod distinguishes between `type casts`:idx: and `type conversions`:idx:. Casts are done with the ``cast`` operator and force the compiler to interpret a bit pattern to be of another type. Type conversions are a much more polite way to convert a type into another: They preserve the abstract *value*, not necessarily the *bit-pattern*. If a type conversion is not possible, the compiler complains or an exception is raised. The syntax for type conversions is ``destination_type(expression_to_convert)`` (like an ordinary call): .. code-block:: nimrod proc getID(x: TPerson): int = return TStudent(x).id The ``EInvalidObjectConversion`` exception is raised if ``x`` is not a ``TStudent``. Object variants --------------- Often an object hierarchy is overkill in certain situations where simple `variant`:idx: types are needed. An example: .. code-block:: nimrod # This is an example how an abstract syntax tree could be modeled in Nimrod type TNodeKind = enum # the different node types nkInt, # a leaf with an integer value nkFloat, # a leaf with a float value nkString, # a leaf with a string value nkAdd, # an addition nkSub, # a subtraction nkIf # an if statement PNode = ref TNode TNode = object case kind: TNodeKind # the ``kind`` field is the discriminator of nkInt: intVal: int of nkFloat: floatVal: float of nkString: strVal: string of nkAdd, nkSub: leftOp, rightOp: PNode of nkIf: condition, thenPart, elsePart: PNode var n: PNode new(n) # creates a new node n.kind = nkFloat n.floatVal = 0.0 # valid, because ``n.kind==nkFloat`` # the following statement raises an `EInvalidField` exception, because # n.kind's value does not fit: n.strVal = "" As can been seen from the example, an advantage to an object hierarchy is that no conversion between different object types is needed. Yet, access to invalid object fields raises an exception. Methods ------- In ordinary object oriented languages, procedures (also called *methods*) are bound to a class. This has disadvantages: * Adding a method to a class the programmer has no control over is impossible or needs ugly workarounds. * Often it is unclear where the method should belong to: is ``join`` a string method or an array method? Nimrod avoids these problems by not assigning methods to a class. All methods in Nimrod are `multi-methods`:idx:. As we will see later, multi-methods are distinguished from procs only for dynamic binding purposes. Method call syntax ------------------ There is a syntactic sugar for calling routines: The syntax ``obj.method(args)`` can be used instead of ``method(obj, args)``. If there are no remaining arguments, the parentheses can be omitted: ``obj.len`` (instead of ``len(obj)``). This `method call syntax`:idx: is not restricted to objects, it can be used for any type: .. code-block:: nimrod echo("abc".len) # is the same as echo(len("abc")) echo("abc".toUpper()) echo({'a', 'b', 'c'}.card) stdout.writeln("Hallo") # the same as writeln(stdout, "Hallo") (Another way to look at the method call syntax is that it provides the missing postfix notation.) So "pure object oriented" code is easy to write: .. code-block:: nimrod import strutils stdout.writeln("Give a list of numbers (separated by spaces): ") stdout.write(stdin.readLine.split.map(parseInt).max.`$`) stdout.writeln(" is the maximum!") Properties ---------- As the above example shows, Nimrod has no need for *get-properties*: Ordinary get-procedures that are called with the *method call syntax* achieve the same. But setting a value is different; for this a special setter syntax is needed: .. code-block:: nimrod type TSocket* = object of TObject FHost: int # cannot be accessed from the outside of the module # the `F` prefix is a convention to avoid clashes since # the accessors are named `host` proc `host=`*(s: var TSocket, value: int) {.inline.} = ## setter of hostAddr s.FHost = value proc host*(s: TSocket): int {.inline.} = ## getter of hostAddr return s.FHost var s: TSocket s.host = 34 # same as `host=`(s, 34) (The example also shows ``inline`` procedures.) The ``[]`` array access operator can be overloaded to provide `array properties`:idx:\ : .. code-block:: nimrod type TVector* = object x, y, z: float proc `[]=`* (v: var TVector, i: int, value: float) = # setter case i of 0: v.x = value of 1: v.y = value of 2: v.z = value else: assert(false) proc `[]`* (v: TVector, i: int): float = # getter case i of 0: result = v.x of 1: result = v.y of 2: result = v.z else: assert(false) The example is silly, since a vector is better modelled by a tuple which already provides ``v[]`` access. Dynamic dispatch ---------------- Procedures always use static dispatch. For dynamic dispatch replace the ``proc`` keyword by ``method``: .. code-block:: nimrod type TExpr = object of TObject ## abstract base class for an expression TLiteral = object of TExpr x: int TPlusExpr = object of TExpr a, b: ref TExpr method eval(e: ref TExpr): int = # override this base method quit "to override!" method eval(e: ref TLiteral): int = return e.x method eval(e: ref TPlusExpr): int = # watch out: relies on dynamic binding return eval(e.a) + eval(e.b) proc newLit(x: int): ref TLiteral = new(result) result.x = x proc newPlus(a, b: ref TExpr): ref TPlusExpr = new(result) result.a = a result.b = b echo eval(newPlus(newPlus(newLit(1), newLit(2)), newLit(4))) Note that in the example the constructors ``newLit`` and ``newPlus`` are procs because they should use static binding, but ``eval`` is a method because it requires dynamic binding. In a multi-method all parameters that have an object type are used for the dispatching: .. code-block:: nimrod type TThing = object of TObject TUnit = object of TThing x: int method collide(a, b: TThing) {.inline.} = quit "to override!" method collide(a: TThing, b: TUnit) {.inline.} = echo "1" method collide(a: TUnit, b: TThing) {.inline.} = echo "2" var a, b: TUnit collide(a, b) # output: 2 As the example demonstrates, invocation of a multi-method cannot be ambiguous: Collide 2 is preferred over collide 1 because the resolution works from left to right. Thus ``TUnit, TThing`` is preferred over ``TThing, TUnit``. **Perfomance note**: Nimrod does not produce a virtual method table, but generates dispatch trees. This avoids the expensive indirect branch for method calls and enables inlining. However, other optimizations like compile time evaluation or dead code elimination do not work with methods. Exceptions ========== In Nimrod `exceptions`:idx: are objects. By convention, exception types are prefixed with an 'E', not 'T'. The `system <system.html>`_ module defines an exception hierarchy that you might want to stick to. Exceptions derive from E_Base, which provides the common interface. Exceptions have to be allocated on the heap because their lifetime is unknown. The compiler will prevent you from raising an exception created on the stack. All raised exceptions should at least specify the reason for being raised in the ``msg`` field. A convention is that exceptions should be raised in *exceptional* cases: For example, if a file cannot be opened, this should not raise an exception since this is quite common (the file may not exist). Raise statement --------------- Raising an exception is done with the ``raise`` statement: .. code-block:: nimrod var e: ref EOS new(e) e.msg = "the request to the OS failed" raise e If the ``raise`` keyword is not followed by an expression, the last exception is *re-raised*. For the purpose of avoiding repeating this common code pattern, the template ``newException`` in the ``system`` module can be used: .. code-block:: nimrod raise newException(EOS, "the request to the OS failed") Try statement ------------- The `try`:idx: statement handles exceptions: .. code-block:: nimrod # read the first two lines of a text file that should contain numbers # and tries to add them var f: TFile if open(f, "numbers.txt"): try: let a = readLine(f) let b = readLine(f) echo "sum: ", parseInt(a) + parseInt(b) except EOverflow: echo "overflow!" except EInvalidValue: echo "could not convert string to integer" except EIO: echo "IO error!" except: echo "Unknown exception!" # reraise the unknown exception: raise finally: close(f) The statements after the ``try`` are executed unless an exception is raised. Then the appropriate ``except`` part is executed. The empty ``except`` part is executed if there is an exception that is not explicitly listed. It is similar to an ``else`` part in ``if`` statements. If there is a ``finally`` part, it is always executed after the exception handlers. The exception is *consumed* in an ``except`` part. If an exception is not handled, it is propagated through the call stack. This means that often the rest of the procedure - that is not within a ``finally`` clause - is not executed (if an exception occurs). If you need to *access* the actual exception object or message inside an ``except`` branch you can use the getCurrentException() and getCurrentExceptionMsg() procs from the `system <system.html>`_ module. Example: .. code-block:: nimrod try: doSomethingHere() except: let e = getCurrentException() msg = getCurrentExceptionMsg() echo "Got exception ", repr(e), " with message ", msg Exception hierarchy ------------------- If you want to create your own exceptions you can inherit from E_Base, but you can also inherit from one of the existing exceptions if they fit your purpose. The exception tree is:: * E_Base * EAsynch * EControlC * ESynch * ESystem * EIO * EOS * EInvalidLibrary * EResourceExhausted * EOutOfMemory * EStackOverflow * EArithmetic * EDivByZero * EOverflow * EAccessViolation * EAssertionFailed * EInvalidValue * EInvalidKey * EInvalidIndex * EInvalidField * EOutOfRange * ENoExceptionToReraise * EInvalidObjectAssignment * EInvalidObjectConversion * EFloatingPoint * EFloatInvalidOp * EFloatDivByZero * EFloatOverflow * EFloatUnderflow * EFloatInexact * EDeadThread See the `system <system.html>`_ module for a description of each exception. Annotating procs with raised exceptions --------------------------------------- Through the use of the optional ``{.raises.}`` pragma you can specify that a proc is meant to raise a specific set of exceptions, or none at all. If the ``{.raises.}`` pragma is used, the compiler will verify that this is true. For instance, if you specify that a proc raises ``EIO``, and at some point it (or one of the procs it calls) starts raising a new exception the compiler will prevent that proc from compiling. Usage example: .. code-block:: nimrod proc complexProc() {.raises: [EIO, EArithmetic].} = ... proc simpleProc() {.raises: [].} = ... Once you have code like this in place, if the list of raised exception changes the compiler will stop with an error specifying the line of the proc which stopped validating the pragma and the raised exception not being caught, along with the file and line where the uncaught exception is being raised, which may help you locate the offending code which has changed. If you want to add the ``{.raises.}`` pragma to existing code, the compiler can also help you. You can add the ``{.effect.}`` pragma statement to your proc and the compiler will output all inferred effects up to that point (exception tracking is part of Nimrod's effect system). Another more roundabout way to find out the list of exceptions raised by a proc is to use the Nimrod ``doc2`` command which generates documentation for a whole module and decorates all procs with the list of raised exceptions. You can read more about Nimrod's `effect system and related pragmas in the manual <manual.html#effect-system>`_. Generics ======== `Generics`:idx: are Nimrod's means to parametrize procs, iterators or types with `type parameters`:idx:. They are most useful for efficient type safe containers: .. code-block:: nimrod type TBinaryTree[T] = object # TBinaryTree is a generic type with # with generic param ``T`` le, ri: ref TBinaryTree[T] # left and right subtrees; may be nil data: T # the data stored in a node PBinaryTree*[T] = ref TBinaryTree[T] # type that is exported proc newNode*[T](data: T): PBinaryTree[T] = # constructor for a node new(result) result.dat = data proc add*[T](root: var PBinaryTree[T], n: PBinaryTree[T]) = # insert a node into the tree if root == nil: root = n else: var it = root while it != nil: # compare the data items; uses the generic ``cmp`` proc # that works for any type that has a ``==`` and ``<`` operator var c = cmp(it.data, n.data) if c < 0: if it.le == nil: it.le = n return it = it.le else: if it.ri == nil: it.ri = n return it = it.ri proc add*[T](root: var PBinaryTree[T], data: T) = # convenience proc: add(root, newNode(data)) iterator preorder*[T](root: PBinaryTree[T]): T = # Preorder traversal of a binary tree. # Since recursive iterators are not yet implemented, # this uses an explicit stack (which is more efficient anyway): var stack: seq[PBinaryTree[T]] = @[root] while stack.len > 0: var n = stack.pop() while n != nil: yield n.data add(stack, n.ri) # push right subtree onto the stack n = n.le # and follow the left pointer var root: PBinaryTree[string] # instantiate a PBinaryTree with ``string`` add(root, newNode("hallo")) # instantiates ``newNode`` and ``add`` add(root, "world") # instantiates the second ``add`` proc for str in preorder(root): stdout.writeln(str) The example shows a generic binary tree. Depending on context, the brackets are used either to introduce type parameters or to instantiate a generic proc, iterator or type. As the example shows, generics work with overloading: the best match of ``add`` is used. The built-in ``add`` procedure for sequences is not hidden and is used in the ``preorder`` iterator. Templates ========= Templates are a simple substitution mechanism that operates on Nimrod's abstract syntax trees. Templates are processed in the semantic pass of the compiler. They integrate well with the rest of the language and share none of C's preprocessor macros flaws. To *invoke* a template, call it like a procedure. Example: .. code-block:: nimrod template `!=` (a, b: expr): expr = # this definition exists in the System module not (a == b) assert(5 != 6) # the compiler rewrites that to: assert(not (5 == 6)) The ``!=``, ``>``, ``>=``, ``in``, ``notin``, ``isnot`` operators are in fact templates: this has the benefit that if you overload the ``==`` operator, the ``!=`` operator is available automatically and does the right thing. (Except for IEEE floating point numbers - NaN breaks basic boolean logic.) ``a > b`` is transformed into ``b < a``. ``a in b`` is transformed into ``contains(b, a)``. ``notin`` and ``isnot`` have the obvious meanings. Templates are especially useful for lazy evaluation purposes. Consider a simple proc for logging: .. code-block:: nimrod const debug = True proc log(msg: string) {.inline.} = if debug: stdout.writeln(msg) var x = 4 log("x has the value: " & $x) This code has a shortcoming: if ``debug`` is set to false someday, the quite expensive ``$`` and ``&`` operations are still performed! (The argument evaluation for procedures is *eager*). Turning the ``log`` proc into a template solves this problem: .. code-block:: nimrod const debug = True template log(msg: string) = if debug: stdout.writeln(msg) var x = 4 log("x has the value: " & $x) The parameters' types can be ordinary types or the meta types ``expr`` (stands for *expression*), ``stmt`` (stands for *statement*) or ``typedesc`` (stands for *type description*). If the template has no explicit return type, ``stmt`` is used for consistency with procs and methods. The template body does not open a new scope. To open a new scope use a ``block`` statement: .. code-block:: nimrod template declareInScope(x: expr, t: typeDesc): stmt {.immediate.} = var x: t template declareInNewScope(x: expr, t: typeDesc): stmt {.immediate.} = # open a new scope: block: var x: t declareInScope(a, int) a = 42 # works, `a` is known here declareInNewScope(b, int) b = 42 # does not work, `b` is unknown (The manual explains why the ``immediate`` pragma is needed for these templates.) If there is a ``stmt`` parameter it should be the last in the template declaration. The reason is that statements can be passed to a template via a special ``:`` syntax: .. code-block:: nimrod template withFile(f: expr, filename: string, mode: TFileMode, body: stmt): stmt {.immediate.} = block: let fn = filename var f: TFile if open(f, fn, mode): try: body finally: close(f) else: quit("cannot open: " & fn) withFile(txt, "ttempl3.txt", fmWrite): txt.writeln("line 1") txt.writeln("line 2") In the example the two ``writeln`` statements are bound to the ``body`` parameter. The ``withFile`` template contains boilerplate code and helps to avoid a common bug: to forget to close the file. Note how the ``let fn = filename`` statement ensures that ``filename`` is evaluated only once. Macros ====== Macros enable advanced compile-time code transformations, but they cannot change Nimrod's syntax. However, this is no real restriction because Nimrod's syntax is flexible enough anyway. To write a macro, one needs to know how the Nimrod concrete syntax is converted to an abstract syntax tree (AST). The AST is documented in the `macros <macros.html>`_ module. There are two ways to invoke a macro: (1) invoking a macro like a procedure call (`expression macros`:idx:) (2) invoking a macro with the special ``macrostmt`` syntax (`statement macros`:idx:) Expression Macros ----------------- The following example implements a powerful ``debug`` command that accepts a variable number of arguments: .. code-block:: nimrod # to work with Nimrod syntax trees, we need an API that is defined in the # ``macros`` module: import macros macro debug(n: varargs[expr]): stmt = # `n` is a Nimrod AST that contains a list of expressions; # this macro returns a list of statements: result = newNimNode(nnkStmtList, n) # iterate over any argument that is passed to this macro: for i in 0..n.len-1: # add a call to the statement list that writes the expression; # `toStrLit` converts an AST to its string representation: result.add(newCall("write", newIdentNode("stdout"), toStrLit(n[i]))) # add a call to the statement list that writes ": " result.add(newCall("write", newIdentNode("stdout"), newStrLitNode(": "))) # add a call to the statement list that writes the expressions value: result.add(newCall("writeln", newIdentNode("stdout"), n[i])) var a: array[0..10, int] x = "some string" a[0] = 42 a[1] = 45 debug(a[0], a[1], x) The macro call expands to: .. code-block:: nimrod write(stdout, "a[0]") write(stdout, ": ") writeln(stdout, a[0]) write(stdout, "a[1]") write(stdout, ": ") writeln(stdout, a[1]) write(stdout, "x") write(stdout, ": ") writeln(stdout, x) Statement Macros ---------------- Statement macros are defined just as expression macros. However, they are invoked by an expression following a colon. The following example outlines a macro that generates a lexical analyzer from regular expressions: .. code-block:: nimrod macro case_token(n: stmt): stmt = # creates a lexical analyzer from regular expressions # ... (implementation is an exercise for the reader :-) nil case_token: # this colon tells the parser it is a macro statement of r"[A-Za-z_]+[A-Za-z_0-9]*": return tkIdentifier of r"0-9+": return tkInteger of r"[\+\-\*\?]+": return tkOperator else: return tkUnknown Term rewriting macros --------------------- Term rewriting macros can be used to enhance the compilation process with user defined optimizations; see this `document <trmacros.html>`_ for further information.


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