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## 1. Data Types

## 1.1 Assoc_Type

Synopsis

  An associative array or hash type

Description

  An `Assoc_Type` object is like an array except that it is indexed using strings and not integers. Unlike an `Array_Type` object, the size of an associative array is not fixed, but grows as objects are added to the array. Another difference is that ordinary arrays represent ordered object; however, the ordering of the elements of an `Assoc_Type` object is unspecified.

  An `Assoc_Type` object whose elements are of some data-type `d` may be created using using

  > `

  >         A = Assoc_Type[d];

  > `

  For example,

  > `

  >         A = Assoc_Type[Int_Type];

  > `

  will create an associative array of integers. To create an associative array capable of storing an arbitrary type, use the form

  > `

  >         A = Assoc_Type[];

  > `

  An optional parameter may be used to specify a default value for array elements. For example,

  > `

  >        A = Assoc_Type[Int_Type, -1];

  > `

  creates an integer-valued associative array with a default element value of -1. Then `A["foo"]` will return -1 if the key `"foo"` does not exist in the array. Default values are available only if the type was specified when the associative array was created.

  The following functions may be used with associative arrays:

  > `

  >         assoc_get_keys
  >         assoc_get_values
  >         assoc_key_exists
  >         assoc_delete_key

  > `

  The `length` function may be used to obtain the number of elements in the array.

  The `foreach` construct may be used with associative arrays via on of the following forms:

  > `

  >           foreach k,v (A) {...}
  >           foreach k (A) using ("keys") { ... }
  >           foreach v (A) using ("values") { ... }
  >           foreach k,v (A) using ("keys", "values") { ... }

  > `

  In all the above forms, the loop is over all elements of the array such that `v=A[k]`.
See Also

  `List_Type, Array_Type, Struct_Type`

## 1.2 List_Type

Synopsis

  A list object

Description

  An object of type `List_Type` represents a list, which is defined as an ordered heterogeneous collection of objects. A list may be created using, e.g.,

  > `

  >         empty_list = {};
  >         list_with_4_items = {[1:10], "three", 9, {1,2,3}};

  > `

  Note that the last item of the list in the last example is also a list. A List_Type object may be manipulated by the following functions:

  > `

  >         list_new
  >         list_insert
  >         list_append
  >         list_delete
  >         list_reverse
  >         list_pop

  > `

  A `List_Type` object may be indexed using an array syntax with the first item on the list given by an index of 0. The `length` function may be used to obtain the number of elements in the list.

  A copy of the list may be created using the @ operator, e.g., `copy = @list`.

  The `foreach` statement may be used with a `List_Type` objects to loop over its elements:

  > `

  >         foreach elem (list) {....}

  > `

See Also

  `Array_Type, Assoc_Type, Struct_Type`

## 1.3 Struct_Type

Synopsis

  A structure datatype

Description

  A `Struct_Type` object with fields `f1`, `f2`,..., `fN` may be created using

  > `

  >         s = struct { f1, f2, ..., fN };

  > `

  The fields may be accessed via the "dot" operator, e.g.,

  > `

  >          s.f1 = 3;
  >          if (s12.f1 == 4) s.f1++;

  > `

  By default, all fields will be initialized to `NULL`.

  A structure may also be created using the dereference operator (@):

  > `

  >         s = @Struct_Type ("f1", "f2", ..., "fN");
  >         s = @Struct_Type ( ["f1", "f2", ..., "fN"] );

  > `

  Functions for manipulating structure fields include:

  > `

  >          _push_struct_field_values
  >          get_struct_field
  >          get_struct_field_names
  >          set_struct_field
  >          set_struct_fields

  > `

  The `foreach` loop may be used to loop over elements of a linked list. Suppose that first structure in the list is called `root`, and that the `child` field is used to form the chain. Then one may walk the list using:

  > `

  >          foreach s (root) using ("child")
  >           {
  >              % s will take on successive values in the list
  >               .
  >               .
  >           }

  > `

  The loop will terminate when the last elements `child` field is NULL. If no ``linking'' field is specified, the field name will default to `next`.

  User-defined data types are similar to the `Struct_Type`. A type, e.g., `Vector_Type` may be created using:

  > `

  >         typedef struct { x, y, z } Vector_Type;

  > `

  Objects of this type may be created via the @ operator, e.g.,

  > `

  >         v = @Vector_Type;

  > `

  It is recommended that this be used in a function for creating such types, e.g.,

  > `

  >         define vector (x, y, z)
  >         {
  >            variable v = @Vector_Type;
  >            v.x = x;
  >            v.y = y;
  >            v.z = z;
  >            return v;
  >         }

  > `

  The action of the binary and unary operators may be defined for such types. Consider the "+" operator. First define a function for adding two `Vector_Type` objects:

  > `

  >         static define vector_add (v1, v2)
  >         {
  >            return vector (v1.x+v2.x, v1.y+v2.y, v1.z, v2.z);
  >         }

  > `

  Then use

  > `

  >         __add_binary ("+", Vector_Type, &vector_add, Vector_Type, Vector_Type);

  > `

  to indicate that the function is to be called whenever the "+" binary operation between two `Vector_Type` objects takes place, e.g.,

  > `

  >         V1 = vector (1, 2, 3);
  >         V2 = vector (8, 9, 1);
  >         V3 = V1 + V2;

  > `

  will assigned the vector (9, 11, 4) to `V3`. Similarly, the `"*"` operator between scalars and vectors may be defined using:

  > `

  >         static define vector_scalar_mul (v, a)
  >         {
  >            return vector (a*v.x, a*v.y, a*v.z);
  >         }
  >         static define scalar_vector_mul (a, v)
  >         {
  >            return vector_scalar_mul (v, a);
  >         }
  >         __add_binary ("*", Vector_Type, &scalar_vector_mul, Any_Type, Vector_Type);
  >         __add_binary ("*", Vector_Type, &vector_scalar_mul, Vector_Type, Any_Type);

  > `

  Related functions include:

  > `

  >         __add_unary
  >         __add_string
  >         __add_destroy

  > `

See Also

  `List_Type, Assoc_Type`

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