11.3.4 Expressions

An expression is either a string expression or a string list expression.

A string expression is either a simple string expression or a compound string expression.

A simple string expression is one of the following:

• A literal string; e.g. "comm/my_proj.gpr"
• A string-valued variable reference (see Variables)
• A string-valued attribute reference (see Attributes)
• An external reference (see External References in Project Files)

A compound string expression is a concatenation of string expressions, using the operator "&"

            Path & "/" & File_Name & ".ads"

A string list expression is either a simple string list expression or a compound string list expression.

A simple string list expression is one of the following:

• A parenthesized list of zero or more string expressions, separated by commas

               File_Names := (File_Name, "gnat.adc", File_Name & ".orig");
               Empty_List := ();
       

• A string list-valued variable reference
• A string list-valued attribute reference

A compound string list expression is the concatenation (using "&") of a simple string list expression and an expression. Note that each term in a compound string list expression, except the first, may be either a string expression or a string list expression.

        File_Name_List := () & File_Name; --  One string in this list
        Extended_File_Name_List := File_Name_List & (File_Name & ".orig");
        --  Two strings
        Big_List := File_Name_List & Extended_File_Name_List;
        --  Concatenation of two string lists: three strings
        Illegal_List := "gnat.adc" & Extended_File_Name_List;
        --  Illegal: must start with a string list