Update for sexpr parser with object API

Moving to parse s-expressions to objects is necessary for eventually
enabling returning also source-location information along with the
parsed nodes, for more informative errors (#9) and source maps (#18).

package.json

@@ -47,7 +47,7 @@
     "esvalid": "1.1.0",
     "nopt": "^3.0.3",
     "prelude-ls": "^1.1.1",
-    "sexpr-plus": "^5.0.1",
+    "sexpr-plus": "^6.0.0",
     "uuid": "^2.0.1"
   }
 }

src/parse.ls

@@ -1,25 +1,14 @@
-# Turns an input S-expression string into a simple tree format based on JS
-# objects.
+# Serves as an adapter from the S-expression parser's format to the internal
+# AST objects.
 
 parse-sexpr = require \sexpr-plus .parse
 { list, atom, string } = require \./ast
 
-# This serves as an adapter from the s-expression module's way of returning
-# things to eslisp AST objects.
-make-explicit = (tree) ->
-  sexpr-type = (thing) ->
-    switch typeof! thing
-    | \String =>
-      switch typeof thing
-      | \object => \string
-      | \string => \atom
-    | \Array => \list
-    | otherwise => null
-
-  switch sexpr-type tree
-  | \list   => list   tree.map make-explicit
-  | \atom   => atom   tree.to-string!
-  | \string => string tree.to-string!
+convert = (tree) ->
+  switch tree.type
+  | \list   => list   tree.content.map convert
+  | \atom   => atom   tree.content
+  | \string => string tree.content
   | null    => throw Error "Unexpected type `#that` (of `#tree`)"
 
-module.exports = parse-sexpr >> make-explicit
+module.exports = parse-sexpr >> convert