Add a power operator

src/grammar.coffee

@@ -526,6 +526,7 @@ grammar =
     o 'Expression -  Expression',               -> new Op '-' , $1, $3
 
     o 'Expression MATH     Expression',         -> new Op $2, $1, $3
+    o 'Expression **       Expression',         -> new Op $2, $1, $3
     o 'Expression SHIFT    Expression',         -> new Op $2, $1, $3
     o 'Expression COMPARE  Expression',         -> new Op $2, $1, $3
     o 'Expression LOGIC    Expression',         -> new Op $2, $1, $3
@@ -560,6 +561,7 @@ operators = [
   ['nonassoc',  '++', '--']
   ['left',      '?']
   ['right',     'UNARY']
+  ['right',     '**']
   ['left',      'MATH']
   ['left',      '+', '-']
   ['left',      'SHIFT']

src/lexer.coffee

@@ -599,6 +599,7 @@ OPERATOR   = /// ^ (
    | ([&|<>])\2=?      # logic / shift
    | \?\.              # soak access
    | \.{2,3}           # range or splat
+   | \*\*              # power
 ) ///
 
 WHITESPACE = /^[^\n\S]+/

src/nodes.coffee

@@ -1406,6 +1406,7 @@ exports.Op = class Op extends Base
     return @compileUnary     o if @isUnary()
     return @compileChain     o if isChain
     return @compileExistence o if @operator is '?'
+    return @compilePower     o if @operator is '**'
     code = @first.compile(o, LEVEL_OP) + ' ' + @operator + ' ' +
            @second.compile(o, LEVEL_OP)
     if o.level <= LEVEL_OP then code else "(#{code})"
@@ -1441,6 +1442,11 @@ exports.Op = class Op extends Base
     parts.push @first.compile o, LEVEL_OP
     parts.reverse() if @flip
     parts.join ''
+
+  compilePower: (o) ->
+    left = @first.compile o, LEVEL_OP
+    right = @second.compile o, LEVEL_OP
+    "Math.pow(#{left}, #{right})"
 
   toString: (idt) ->
     super idt, @constructor.name + ' ' + @operator

test/operators.coffee

@@ -269,3 +269,12 @@ test "Regression with implicit calls against an indented assignment", ->
     1
 
   eq a, 1
+
+test "power operator", ->
+  eq 27, 3 ** 3
+
+test "power operator has higher precedence than other maths operators", ->
+  eq 55, 1 + 3 ** 3 * 2
+
+test "power operator is right associative", ->
+  eq 2, 2 ** 1 ** 3