Replace delimited identifier syntax

Fixes #243.
Fixes #193.

lang/lib/array.bal

@@ -33,8 +33,8 @@ public function enumerate(Type[] arr) returns [int, Type][] = external;
 
 // Functional iteration
 
-// use delimited identifer for function name to avoid conflict with reserved name
-public function ^"map"(Type[] arr, function(Type val) returns Type1 func) returns Type1[] = external;
+// use quoted identifer for function name to avoid conflict with reserved name
+public function 'map(Type[] arr, function(Type val) returns Type1 func) returns Type1[] = external;
 # Applies `func` to each member of `arr`.
 public function forEach(Type[] arr, function(Type val) returns () func) returns () = external;
 public function filter(Type[] arr, function(Type val) returns boolean func) returns Type[] = external;

lang/lib/map.bal

@@ -36,8 +36,8 @@ public function entries(map<Type> m) returns map<[string, Type]> = external;
 
 // Functional iteration
 
-// use delimited identifer for function name to avoid conflict with reserved name
-public function ^"map"(map<Type> m, function(Type val) returns Type1 func) returns map<Type1> = external;
+// use quoted identifer for function name to avoid conflict with reserved name
+public function 'map(map<Type> m, function(Type val) returns Type1 func) returns map<Type1> = external;
 # Applies `func` to each member of `m`.
 public function forEach(map<Type> m, function(Type val) returns () func) returns () = external;
 public function filter(map<Type> m, function(Type val) returns boolean func) returns map<Type> = external;

lang/spec.html

@@ -283,12 +283,18 @@ <h2 id="lexical_structure">4. Lexical structure</h2>
 </p>
 
 <pre
-class="grammar">identifier := UndelimitedIdentifier | DelimitedIdentifier
-UndelimitedIdentifier :=
+class="grammar">identifier := UnquotedIdentifier | QuotedIdentifier
+UnquotedIdentifier :=
    IdentifierInitialChar IdentifierFollowingChar*
-DelimitedIdentifier := <code>^"</code> StringChar+ <code>"</code>
-IdentifierInitialChar := <code>A</code> .. <code>Z</code> | <code>a</code> .. <code>z</code> | <code>_</code> | UnicodeIdentifierChar
+QuotedIdentifier := <code>'</code> QuotedIdentifierChar+
+QuotedIdentifierChar :=
+  IdentifierFollowingChar
+  | QuotedIdentifierEscape
+  | StringNumericEscape
+IdentifierInitialChar :=  AsciiLetter | <code>_</code> | UnicodeIdentifierChar
 IdentifierFollowingChar := IdentifierInitialChar | Digit
+QuotedIdentifierEscape := <code>\</code> ^ ( AsciiLetter | 0x9 | 0xA | 0xD | UnicodePatternWhiteSpaceChar )
+AsciiLetter := <code>A</code> .. <code>Z</code> | <code>a</code> .. <code>z</code>
 UnicodeIdentifierChar := ^ ( AsciiChar | UnicodeNonIdentifierChar )
 AsciiChar := 0x0 .. 0x7F
 UnicodeNonIdentifierChar :=
@@ -309,6 +315,12 @@ <h2 id="lexical_structure">4. Lexical structure</h2>
 of Unicode TR31 for immutable identifiers; the set of characters is immutable in
 the sense that it does not change between Unicode versions.
 </p>
+<p>
+The QuotedIdentifier syntax allows an arbitrary non-empty string to be treated
+as an identifier. In particular, a reserved keyword <code><var>K</var></code>
+can be used as an identifier by preceding it with a single quote i.e.
+<code>'<var>K</var></code>.
+</p>
 
 <pre
 class="grammar">TokenWhiteSpace := (Comment | WhiteSpaceChar)*
@@ -6024,6 +6036,8 @@ <h3>Summary of changes from 2019R1 to 2019R2</h3>
 rather than <code>anydata|error</code>.</li>
 <li>Calls using <code>start</code> are treated as actions, and so are not
 allowed within expressions.</li>
+<li>There is a new syntax for allowing arbitrary strings as identifiers to
+replace the old delimited identifier syntax <code>^"<var>s</code>"</code>.</li>
 </ol>
 
 <h3>Summary of changes from 0.990 to 2019R1</h3>