7.4 Virtual Strings

The module VirtualString contains procedures operating on virtual strings. Virtual strings are designed as a convenient way to combine strings, byte strings, atoms, integers and floats to compound strings without explicit concatenation and conversion.

IsVirtualString

{VirtualString.is +X ?B}

tests whether X is a virtual string. Virtual strings are defined recursively as the set of all integers, floats, atoms, strings, byte strings, and tuples with label '#' whose subtrees are virtual strings.

toString

{VirtualString.toString +V ?S}

converts a virtual string V to a string S.

The transformation is straightforward: Atoms (except nil and '#'), integers, floats and byte strings are transformed into strings using Atom.toString, Int.toString, Float.toString, and ByteString.toString respectively, where in numbers - is used instead of ~. A tuple with label '#' is transformed by concatenation of the transformed subtrees. Note that both nil and '#' denote the empty string.

The following relation holds for all virtual strings V1 and V2:

{VirtualString.toString V1#V2}
= {Append
   {VirtualString.toString V1}
   {VirtualString.toString V2}}

Thus, VirtualString.toString maps # homomorphically to Append.

toAtom

{VirtualString.toAtom +V ?A}

converts a virtual string V to an atom A.

This procedure can be defined as:

fun {VirtualString.toAtom V}
   {String.toAtom {VirtualString.toString V}}
end

toByteString

{VirtualString.toByteString +V ?ByteString}

converts a virtual string V to a byte string ByteString.

This procedure is a synonym of ByteString.make (which see).

length

{VirtualString.length +V ?I}

returns the length of a virtual string in characters. Can be defined as:

{Length {VirtualString.toString V} I}

changeSign

{VirtualString.changeSign +V1 X ?V2}

returns a virtual string derived from V1 where all occurrences of the unary minus sign for integers and floats are replaced by X.