STRING documentation.

doc/wiki/eberon-strings.md

@@ -0,0 +1,28 @@
+A new basic type STRING is introduced because oberon has nothing to deal with strings of arbitrary length. Any possible library solution will have a lot of syntax noise and have no chance to optimize trivial string operations. Oberon is not C++ with all these complex things (like operator overloading etc.) which make library solution viable so it is simplier to just support a new basic type on compiler level.
+
+### Semantics
+STRING is a basic type. It represents a sequence of characters of any length (including zero - empty string).
+STRING is very similar to ARRAY OF CHAR:
+* STRING can be indexed [] as CHAR
+* predefined procedure LEN returns the length of STRING
+* STRING can be compared
+* STRING can be assigned from string literal
+* STRING can be passed as open non-VAR ARRAY OF CHAR
+
+But also there are differences:
+* STRING content is read-only, it never modified
+* ARRAY OF CHAR cannot be assigned to STRING or passed as STRING
+* STRING can be returned as a result of procedure
+
+STRING supports concatenation through '+' operator. Also '+' is supported for string literals:
+
+Example:
+
+    CONST constString = 22X + "abc" + 22X;
+    VAR s: STRING;
+    ...
+    s := s + constString + s;
+
+STRING [default value](/vladfolts/oberonjs/wiki/Original-report-refinements#2-variables-default-values) is empty string - "". STRING cannot be NIL.
+
+All special cases described in original Wirth report regarding to ARRAY OF CHAR (comparing to other array types) seem not actual after introducing a separate type STRING to support strings but they are left as is in [Eberon](/vladfolts/oberonjs/wiki/eberon) to maintain compatibility with original oberon.

doc/wiki/eberon.md

@@ -4,4 +4,5 @@ Eberon extends original Oberon so any valid oberon program is also a valid ebero
 
 ### Extensions
 * [Methods](/vladfolts/oberonjs/wiki/eberon-methods)
+* [Strings](/vladfolts/oberonjs/wiki/eberon-strings)
 * Non-scalar variables (arrays and records) can be exported (forbidden in oberon for some unknown reason).

doc/wiki/refinements.md

@@ -61,7 +61,7 @@ Full example:
 
 2. Variables default values
 ---------------------------
-All variables have zero as a default value (before first assignment). For pointer/procedure types it is NIL. For sets - empty set.
+All variables have zero as a default value (before first assignment). For pointer/procedure types it is NIL. For sets - empty set. For STRING - empty string.
 
     MODULE m;
     VAR r: RECORD field: INTEGER END;