Changes between Version 99 and Version 100 of IR2

Timestamp:

05/14/21 10:41:03 (5 years ago)

Author:

siegel

Comment:

--

IR2

@@ -17 +17 @@
 
 1. **Do variables have default initial values?**
-  * No.  Every variable must be explicitly initialized.  However, `$undef` can be used as the initializer, indicating that the variable is undefined.  Even in this case, the variable has some unspecified value of its type.   Details are below.
+  * No.  Every variable (other than a variable designating a system or abstract function) must must be explicitly initialized.  However, `$undef` can be used as the initializer, indicating that the variable is undefined.  Even in this case, the variable has some unspecified value of its type.   Details are below.
 1. **How do you initialize a variable?**
-  * In the declaration.   For example `n=$new($int);` will assign `n` an arbitrary integer, while `n=0;` will assign the integer `0` to `n`.
+  * In the declaration.   For example `$int n=$new($int);` will assign `n` an arbitrary integer, while `$int n=0;` will assign the integer `0` to `n`.
 1. **How is an array allocated?**
-  * An array variable `a` is declared with a decl such as `T a[] = $new_array(n, T);` which assigns to `a` a new array value for an array of length `n` of elements of type `T` in which all entries are undefined.   (Alternatively, `T a[] = $new(T[n])` will create an array of arbitrary defined values.)  For heap-allocation, `T * p = $undef;` followed by the statement `p = $alloc(&heap, n, T);` will add a new object to the heap and return a pointer to the first element.  An `$alloc`-ed object can be deallocated with `$free(p);`.
+  * An array variable `a` is declared with a decl such as `T a[] = $new_array(n, T);` which assigns to `a` a new array value for an array of length `n` of elements of type `T` in which all entries are undefined.   (Alternatively, `T a[] = $new(T[n])` will create an array of arbitrary defined values.)  For heap-allocation, `T * p = $undef;` followed by the statement `p = $alloc<T>(&heap, n);` will add a new object to the heap and return a pointer to the first element.  An `$alloc`-ed object can be deallocated with `$free(p);`.
 1. **Is there an "array-pointer pun", as in C?**
   * No, if you want a pointer to element 0 of an array, you have to explicitly write something like `&a[0]`.
@@ -155 +155 @@
 * Arrays are similar to sequences.   The main differences are as follows:
   * An object (i.e., a variable or component of an object) of array type is initialized once, then will never be assigned to again.   Hence there cannot be a statement of the form `a=...` where `a` has array type.
-  * After initialization, an object or array type can appear only as the first (left) argument to the subscript operator `[]` or as the argument to the `$length` operator.
+  * After initialization, an object of array type can appear only as the first (left) argument to the subscript operator `[]` or as the argument to the `$length` operator.
   * Arrays are mutable.   As in C, the left hand size of an assignment may have the form `a[i]`, where `a` is an object of array type.  Sequences are immutable.
   * Elements of an array are addressable, i.e., one can form a pointer such as `&a[i]`.  This is not possible with sequences, sets, maps, or relations---there is no way to have a pointer to any component of such a type.