Merge pull request #329 from FeepingCreature/master

[neat/en] Document Neat language

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+---
+
+language: neat
+contributors:
+    - ["Feep", "https://github.com/FeepingCreature"]
+filename: LearnNeat.nt
+
+---
+
+Neat is basically a smaller version of D1 with some experimental syntax and a focus on terseness without losing the basic C-like syntax.
+
+[Read more here.](https://github.com/FeepingCreature/fcc/wiki)
+
+```D
+// single line comments start with //
+/*
+  multiline comments look like this
+*/
+/+
+  or this
+  /+ these can be nested too, same as D +/
++/
+
+// Module name. This has to match the filename/directory.
+module LearnNeat;
+
+// Make names from another module visible in this one.
+import std.file;
+// You can import multiple things at once.
+import std.math, std.util;
+// You can even group up imports!
+import std.(process, socket);
+
+// Global functions!
+void foo() { }
+
+// Main function, same as in C.
+// string[] == "array of strings".
+// "string" is just an alias for char[],
+void main(string[] args) {
+  // Call functions with "function expression".
+  writeln "Hello World";
+  // You can do it like in C too... if you really want.
+  writeln ("Hello World");
+  // Declare a variable with "type identifier"
+  string arg = ("Hello World");
+  writeln arg;
+  // (expression, expression) forms a tuple.
+  // There are no one-value tuples though.
+  // So you can always use () in the mathematical sense.
+  // (string) arg; <- is an error
+  
+  /*
+    byte: 8 bit signed integer
+      char: 8 bit UTF-8 byte component.
+    short: 16 bit signed integer
+    int: 32 bit signed integer
+    long: 64 bit signed integer
+    
+    float: 32 bit floating point
+    double: 64 bit floating point
+    real: biggest native size floating point (80 bit on x86).
+    
+    bool: true or false
+  */
+  int a = 5;
+  bool b = true;
+  // as in C, && and || are short-circuit evaluating.
+  b = b && false;
+  assert(b == false);
+  // "" are "format strings". So $variable will be substituted at runtime
+  // with a formatted version of the variable.
+  writeln "$a";
+  // This will just print $a.
+  writeln `$a`;
+  // you can format expressions with $()
+  writeln "$(2+2)";
+  // Note: there is no special syntax for characters.
+  char c = "a";
+  // Cast values by using type: expression.
+  // There are three kinds of casts:
+  // casts that just specify conversions that would be happening automatically
+  // (implicit casts)
+  float f = float:5;
+  float f2 = 5; // would also work
+  // casts that require throwing away information or complicated computation -
+  // those must always be done explicitly
+  // (conversion casts)
+  int i = int:f;
+  // int i = f; // would not work!
+  // and, as a last attempt, casts that just reinterpret the raw data.
+  // Those only work if the types have the same size.
+  string s = "Hello World";
+  // Arrays are (length, pointer) pairs.
+  // This is a tuple type. Tuple types are (type, type, type).
+  // The type of a tuple expression is a tuple type. (duh)
+  (int, char*) array = (int, char*): s;
+  // You can index arrays and tuples using the expression[index] syntax.
+  writeln "pointer is $(array[1]) and length is $(array[0])";
+  // You can slice them using the expression[from .. to] syntax.
+  // Slicing an array makes another array.
+  writeln "$(s[0..5]) World";
+  // Alias name = expression gives the expression a name.
+  // As opposed to a variable, aliases do not have an address
+  // and can not be assigned to. (Unless the expression is assignable)
+  alias range = 0 .. 5;
+  writeln "$(s[range]) World";
+  // You can iterate over ranges.
+  for int i <- range {
+    write "$(s[i])";
+  }
+  writeln " World";
+  // Note that if "range" had been a variable, it would be 'empty' now!
+  // Range variables can only be iterated once.
+  // The syntax for iteration is "expression <- iterable".
+  // Lots of things are iterable.
+  for char c <- "Hello" { write "$c"; }
+  writeln " World";
+  // For loops are "for test statement";
+  alias test = char d <- "Hello";
+  for test write "$d";
+  writeln " World\t\x05"; // note: escapes work
+  // Pointers: function the same as in C, btw. The usual.
+  // Do note: the pointer star sticks with the TYPE, not the VARIABLE!
+  string* p;
+  assert(p == null); // default initializer
+  p = &s;
+  writeln "$(*p)";
+  // Math operators are (almost) standard.
+  int x = 2 + 3 * 4 << 5;
+  // Note: XOR is "xor". ^ is reserved for exponentiation (once I implement that).
+  int y = 3 xor 5;
+  int z = 5;
+  assert(z++ == 5);
+  assert(++z == 7);
+  writeln "x $x y $y z $z";
+  // As in D, ~ concatenates.
+  string hewo = "Hello " ~ "World";
+  // == tests for equality, "is" tests for identity.
+  assert  (hewo == s);
+  assert !(hewo is s);
+  // same as
+  assert  (hewo !is s);
+  
+  // Allocate arrays using "new array length"
+  int[] integers = new int[] 10;
+  assert(integers.length == 10);
+  assert(integers[0] == 0); // zero is default initializer
+  integers = integers ~ 5; // This allocates a new array!
+  assert(integers.length == 11);
+  
+  // This is an appender array.
+  // Instead of (length, pointer), it tracks (capacity, length, pointer).
+  // When you append to it, it will use the free capacity if it can.
+  // If it runs out of space, it reallocates - but it will free the old array automatically.
+  // This makes it convenient for building arrays.
+  int[auto~] appender;
+  appender ~= 2;
+  appender ~= 3;
+  appender.free(); // same as {mem.free(appender.ptr); appender = null;}
+  
+  // Scope variables are automatically freed at the end of the current scope.
+  scope int[auto~] someOtherAppender;
+  // This is the same as:
+  int[auto~] someOtherAppender2;
+  onExit { someOtherAppender2.free; }
+  
+  // You can do a C for loop too
+  // - but why would you want to?
+  for (int i = 0; i < 5; ++i) { }
+  // Otherwise, for and while are the same.
+  while int i <- 0..4 {
+    assert(i == 0);
+    break; // continue works too
+  } then assert(false); // if we hadn't break'd, this would run at the end
+  // This is the height of loopdom - the produce-test-consume loop.
+  do {
+    int i = 5;
+  } while (i == 5) {
+    assert(i == 5);
+    break; // otherwise we'd go back up to do {
+  }
+  
+  // This is a nested function.
+  // Nested functions can access the surrounding function.
+  string returnS() { return s; }
+  writeln returnS();
+  
+  // Take the address of a function using &
+  // The type of a global function is ReturnType function(ParameterTypeTuple).
+  void function() foop = &foo;
+  
+  // Similarly, the type of a nested function is ReturnType delegate(ParameterTypeTuple).
+  string delegate() returnSp = &returnS;
+  writeln returnSp();
+  // Class member functions and struct member functions also fit into delegate variables.
+  // In general, delegates are functions that carry an additional context pointer.
+  // ("fat pointers" in C)
+  
+  // Allocate a "snapshot" with "new delegate".
+  // Snapshots are not closures! I used to call them closures too,
+  // but then my Haskell-using friends yelled at me so I had to stop.
+  // The difference is that snapshots "capture" their surrounding context
+  // when "new" is used.
+  // This allows things like this
+  int delegate(int) add(int a) {
+    int add_a(int b) { return a + b; }
+    // This does not work - the context of add_a becomes invalid
+    // when add returns.
+    // return &add_a;
+    // Instead:
+    return new &add_a;
+  }
+  int delegate(int) dg = add 2;
+  assert (dg(3) == 5);
+  // or
+  assert (((add 2) 3) == 5);
+  // or
+  assert (add 2 3 == 5);
+  // add can also be written as
+  int delegate(int) add2(int a) {
+    // this is an implicit, nameless nested function.
+    return new λ(int b) { return a + b; }
+  }
+  // or even
+  auto add3(int a) { return new λ(int b) -> a + b; }
+  // hahahaaa
+  auto add4 = λ(int a) -> new λ(int b) -> a + b;
+  assert(add4 2 3 == 5);
+  // If your keyboard doesn't have a λ (you poor sod)
+  // you can use \ too.
+  auto add5 = \(int a) -> new \(int b) -> a + b;
+  // Note!
+  auto nestfun = λ() { } // There is NO semicolon needed here!
+  // "}" can always substitute for "};".
+  // This provides syntactic consistency with built-in statements.
+  
+  
+  // This is a class.
+  // Note: almost all elements of Neat can be used on the module level
+  //       or just as well inside a function.
+  class C {
+    int a;
+    void writeA() { writeln "$a"; }
+    // It's a nested class - it exists in the context of main().
+    // so if you leave main(), any instances of C become invalid.
+    void writeS() { writeln "$s"; }
+  }
+  C cc = new C;
+  // cc is a *reference* to C. Classes are always references.
+  cc.a = 5; // Always used for property access.
+  auto ccp = &cc;
+  (*ccp).a = 6;
+  // or just
+  ccp.a = 7;
+  cc.writeA();
+  cc.writeS(); // to prove I'm not making things up
+  // Interfaces work same as in D, basically. Or Java.
+  interface E { void doE(); }
+  // Inheritance works same as in D, basically. Or Java.
+  class D : C, E {
+    override void writeA() { writeln "hahahahaha no"; }
+    override void doE() { writeln "eeeee"; }
+    // all classes inherit from Object. (toString is defined in Object)
+    override string toString() { return "I am a D"; }
+  }
+  C cd = new D;
+  // all methods are always virtual.
+  cd.writeA();
+  E e = E:cd; // dynamic class cast!
+  e.doE();
+  writeln "$e"; // all interfaces convert to Object implicitly.
+  
+  // Templates!
+  // Templates are parameterized namespaces, taking a type as a parameter.
+  template Templ(T) {
+    alias hi = 5, hii = 8;
+    // Templates always have to include something with the same name as the template
+    // - this will become the template's _value_.
+    // Static ifs are evaluated statically, at compile-time.
+    // Because of this, the test has to be a constant expression,
+    // or something that can be optimized to a constant.
+    static if (types-equal (T, int)) {
+      alias Templ = hi;
+    } else {
+      alias Templ = hii;
+    }
+  }
+  assert(Templ!int == 5);
+  assert(Templ!float == 8);
+}
+```
+
+## Topics Not Covered
+
+ * Extended iterator types and expressions
+ * Standard library
+ * Conditions (error handling)
+ * Macros