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|Why has the representation of double quoted text changed?
Prolog defines two forms of quoted text. Traditionally, single quoted text is mapped to atoms while double quoted text is mapped to a list of character codes (integers) or characters (atoms of length 1). Representing text using atoms is often considered inadequate for several reasons:
Representing text as lists, be it of character codes or characters, also comes at a price:
could be used to indicate that we are dealing with a string.
Lacking runtime information, debuggers and the toplevel can only use heuristics to decide whether to print a list of integers as such or as a string (see portray_text/1).
While experienced Prolog programmers have learned to cope with this, we still consider this an unfortunate situation.