Upgrading from Mosel 5 to Mosel 6

Topics covered in this section:

The new language features introduced by Mosel 6 are largely incremental to the existing functionality and language syntax. However, a few quite specific points relating to the use of undeclared list or set structures may require updates to existing Mosel source code.

Types of undeclared lists

Mosel 6 allows the user to define lists that contain elements of different types, any such mixed type list now results in a list of any. With previous versions of Mosel a combination of the numerical types real and integer was permitted, resulting in the type list of real.

1. Constant lists combining types real and integer: In order to obtain the same type list of real with Mosel 6, all integer values need to be cast explicitly to real when defining constant lists of numerical values (LR) or be specified as real numbers (LR2):

   declarations
     LC=[1,2.5]                ! Mosel 5: list of real; Mosel 6: list of any
     LR=[real(1),2.5]          ! Mosel 5+6: list of real
     LR2=[1.0,2.5]             ! Mosel 5+6: list of real
   end-declarations

   As a consequence of the change of type for list LC in the code snippet above, Mosel 5 code accessing elements of this list, such as

   declarations
     myval: real
   end-declarations
   myval:= LC(2)

   will result in an error message "Incompatible types in assignment" with Mosel 6.
2. Non-constant lists combining types real and integer: For non-constant lists that were previously undeclared and hence relied on the automatic type deduction it will be sufficient to add a suitable declaration:

   declarations
     LD: list of real
   end-declarations
   LA:=[1,2.5]                 ! Mosel 5: list of real; Mosel 6: list of any
   LD:=[1,2.5]                 ! Mosel 5+6: list of real

Unnamed array index sets

Mosel 6 makes it possible to work with unnamed index sets in places where this was previously not possible, including in the definition of arrays that are used as fields in record structures. As a consequence of the revised set handling, a few cases where unnamed sets were already accepted in previous releases now behave in a more systematic way that is different from previous behaviour: unless two arrays specifically are declared to take the same (named) index, their sets are now always treated as being different, including for single line declarations of multiple arrays. As a result, code such as the following that works with previous versions of Mosel:

public declarations
  A,B: array(set of string) of integer
  data=`
data:[('a') [1 2] ('b') [3 4]]
`
end-declarations

initialisations from 'mmsystem.text:data'
  [A,B] as 'data'
end-initialisations

will fail with the error message "Incompatible types for 'initialisations'". The correction consists in adding a name for the set in the array declaration in order to make sure that both arrays have indeed the same index set:

public declarations
  A,B: array(S: set of string) of integer
end-declarations