BNF Using Scala Parser Combinators

def pNumericConst = regex(new Regex("[0-9]+"))
def pStringConst = regex(new Regex("\"([^\"]|(\\\"))*\""))
def pColorConst = regex(new Regex("0x[A-Fa-f0-9]{6}"))
def pId = regex(new Regex("[A-Za-z][A-Za-z0-9]*"))
def pBooleanConst = regex(new Regex("(true)|(false)"))
def pTextStyleConst = regex(new Regex("(bold)|(italic)|(regular)"))
def pHAlignConst = regex(new Regex("(top)|(middle)|(bottom)"))
def pVAlignConst = regex(new Regex("(left)|(center)|(right)"))

def pNumericExpr = pNumericConst;
def pStringExpr =  pStringConst;
def pColorExpr = pColorConst;
def pBooleanExpr = pBooleanConst;
def pTextStyleExpr = pTextStyleConst
def pHAlignExpr = pHAlignConst
def pVAlignExpr = pVAlignConst

def Program      = WidgetSpec *
def WidgetSpec   = pId ~ "<-" ~ Widget

def Widget       = (AtomicWidget
                    | (AtomicWidget ~   "|"   ~ AtomicWidget)
                    | (AtomicWidget ~  "---"  ~ AtomicWidget)
                    | (AtomicWidget ~  "*|*"  ~ RangeSpec)
                    | (AtomicWidget ~ "*---*" ~ RangeSpec)
                    | ("(" ~ AtomicWidget ~ ")"))

def RangeSpec = pId ~ "=" ~ pNumericExpr ~ ":" ~ pNumericExpr
def AtomicWidget = (("(" ~ WidgetDef ~ ")")
                    | ("(" ~ WidgetDef ~ ")" ~ "[" ~ (WidgetProp *)  ~ "]"))

def WidgetName = ("label" | "textbox" | "button" | "checkbox" | "radio" |
                    "image" | "combobox" | "slider")

def WidgetDef    = (WidgetName
                    | (WidgetName ~ ":" ~ WidgetDim ~ "x" ~ WidgetDim))

def WidgetDim    = (("(" ~ pNumericExpr ~ ")") | "?" | pNumericExpr)

def WidgetProp = (("text" ~ "=" ~ pStringExpr)
                 | ("image" ~ "=" ~ pStringExpr)
                 | ("checked" ~ "=" ~ pBooleanExpr)
                 | ("value" ~ "=" ~ pNumericExpr)
                 | ("enabled" ~ "=" ~ pBooleanExpr)
                 | ("fgcolor" ~ "=" ~ pColorConst)
                 | ("bgcolor" ~ "=" ~ pColorConst)
                 | ("font" ~ "=" ~ "(" ~ pStringExpr ~ "," ~ pNumericExpr ~ "," ~ pTextStyleExpr ~ ")")
                 | ("halign" ~ "=" ~ pHAlignExpr)
                 | ("valign" ~ "=" ~ pVAlignExpr)
                 | ("minval" ~ "=" ~ pNumericExpr)
                 | ("maxval" ~ "=" ~ pNumericExpr))