

Strings


a)  The  keyword  %string  may  always   be   followed   by   a   length
    specification.

    Thus    %string(10)%array %name ....
     and    %string(255)%name ......

    are permitted.

    In   EMAS  2900  IMP80,  no  use  is  made  of  the  maximum  length
    specification for string name and string array name variables.


    [In other IMP80 implementations, however,  a  string  name  variable
    must  have a maximum length specification and can only refer to ("be
    pointed at") a string variable of  the  SAME  maximum  length.   The
    forms
            %string(*)%array %name .....
            %string(*)%name ...........

    are  also  provided,  however,  to  enable declarations of reference
    variables which can point at any string variable.]


b)  The string function FROMSTRING is renamed SUBSTRING.

c)  A string resolution of the form

            S -> (A).B

    succeeds in IMP9 only if string S starts with string  expression  A.
    In IMP80, however, the resolution is interpreted as being equivalent
    to  S  ->  JUNK.(A).B where JUNK is a "hidden" string(255) variable;
    that is, the resolution will succeed if A appears ANYWHERE within S.

    When converting an IMP9 program to IMP80, the following  translation
    is recommended:

            %if S -> (B).C %then ...                         in IMP9
    becomes
            %if S -> NS1.(B).NS2 %and NS1="" %then C=NS2 %and ...
                                                             in IMP80

        [NS1 and NS2 are new %string(255) variables]


    This translation is still valid when the IMP9 statement is
 
            %if S -> (B).S %then ...
 
    i.e. when C is S.
 
    Unconditional resolutions can normally remain unchanged; they  might
    succeed  in  IMP80  where  they  would fail in IMP9, but this is not
    significant unless you are expecting them to fail.