awwx.ws

Creating a parser combinator library to parse JSON

Skipping whitespace

By happy happenstance, the JSON definition of whitespace is the same as Arc’s, so skipping whitespace is easy:

(def skipw (p)
  (mem nonwhite p))

arc> (show-parse json-true:skipw "   true")
returning: t remaining: 
nil

I’ll make that into a combinator. When passed a parser, it will return a parser that first skips whitespace, and then runs the passed parser:

(def skipwhite (parser)
  (fn (p)
    (parser (skipw p))))

arc> (show-parse (skipwhite json-true) "   true")
returning: t remaining: 
nil

Now I have a json-value parser that will skip whitespace before any JSON value:

(= json-value
  (skipwhite:alt json-true
                 json-false
                 json-null))

arc> (show-parse json-value "  false,1,2")
returning: nil remaining: ,1,2
nil

arc> (fromjson "  true")
t

Questions? Comments? Email me andrew.wilcox [at] gmail.com