start work on a recursive descent parser

janet/myparser.janet

@@ -387,6 +387,7 @@ if (:)foo then :bar else :baz
 (comment
 
 Okay, so I'm trying to figure out how to manage panics in this declarative (not recursive-descent) parser.
-The question is how to 
-
+The question is how to do the thing where we pop out of the stack up to the most relevant rule.
+Given that we may have deeply nested rules, we either want:
+	- A stack of rules in the parser, which
 )

janet/recursive.janet

@@ -0,0 +1,109 @@
+### A recursive descent parser for Ludus
+
+
+### First, some mutual recursion helpers
+(defn unreachable 
+ "A function that errors out if called."
+ [&] (error "cannot call recursive function before definition"))
+
+(defmacro declare
+ "Forward-declares a function name, so that it can be called in a mutually recursive manner."
+ [& names]
+  (def bindings @[])
+  (loop [name :in names]
+   (def binding ~(var ,name unreachable))
+   (array/push bindings binding))
+  ~(upscope ,;bindings))
+
+(defmacro defrec 
+ "Defines a function depended on by another function, that has been forward `declare`d."
+ [name & forms]
+  (if-not (dyn name) (error "recursive functions must be declared before they are defined"))
+  ~(set ,name (defn ,name ,;forms)))
+
+### Next: a data structure for a parser
+(defn- new-parser [tokens]
+ @{
+  :tokens (tokens :tokens)
+  :ast @[]
+  :current 0
+  :errors @[]
+ })
+
+### and some helper functions for interfacing with that data structure
+(defn- current [parser] (get (parser :tokens) (parser :current)))
+
+(defn- peek [parser] (get (parser :tokens) (inc (parser :current))))
+
+(defn- advance [parser] (update parser :current inc))
+
+(defn- type [token] (get token :type))
+
+(defn- expect [parser type]
+ (def current-type (-> parser current (get :type)))
+ (= type current-type))
+
+### Parsing functions
+(declare expr)
+
+# atoms
+(defn- bool [parser] 
+ (def curr (-> parser current))
+ (def ttype (type curr))
+ (def value (if (= ttype :true) true false))
+ (def ast {:type :bool :value value :token curr})
+ (update parser :ast array/push ast)
+ (advance parser))
+
+(defn- num [parser]
+ (def curr (-> parser current))
+ (def ast {:type :number :value (curr :literal) :token curr})
+ (update parser :ast array/push ast)
+ (advance parser))
+
+(defn- kw [parser]
+ (def curr (-> parser current))
+ (def ast {:type :keyword :value (curr :literal) :token curr})
+ (update parser :ast array/push ast)
+ (advance parser))
+
+(defn- nill [parser]
+ (def ast {:type :nil :token (current parser)})
+ (update parser :ast array/push ast)
+ (advance parser))
+
+(defn- str [parser]
+ (def curr (-> parser current))
+ (def ast {:type :string :value (curr :literal) :token curr})
+ (update parser :ast array/push ast)
+ (advance parser))
+
+(defrec expr [parser]
+ (def curr (current parser))
+ (case (type curr)
+  # atoms
+  :nil (nill parser)
+  :true (bool parser)
+  :false (bool parser)
+  :number (num parser)
+  :keyword (kw parser)
+
+  # strings
+  :string (str parser)
+  ### TODO: interpolated strings
+
+ )
+)
+
+(do
+#(comment
+(os/cd "janet") # For repl to do relative imports
+(import ./scanner :as s)
+
+(def scanned (s/scan "\"foo bar baz\""))
+(def a-parser (new-parser scanned))
+(def parsed (expr a-parser))
+(-> parsed (get :ast) (get 0) (get :value))
+)
+
+

janet/scanner.janet

@@ -192,12 +192,13 @@
   [scanner]
   (print "Adding string")
   (defn recur [scanner buff interpolate?]
-    (print "\n printing a thing from add-stirng" buff)
     (let [char (current-char scanner)]
       (case char
         "{" (recur (advance scanner) (buffer/push buff char) true)
         # allow multiline strings
         "\n" (recur (update (advance scanner) :line inc) (buffer/push buff char) interpolate?)
+        ### TODO: add interpolated strings
+        ### :string -> (if (interpolate? :interpolated :string))
         "\"" (add-token (advance scanner) :string (string buff))
         "\\" (let [next (next-char scanner)
                  scanner (if (= next "\n")
@@ -314,7 +315,7 @@
   (put scanner :start (get scanner :current)))
 
 (defn scan [source &opt input]
-  (default input "")
+  (default input :input)
   (defn recur [scanner]
     (if (at-end? scanner)
       (let [scanner (add-token (add-token scanner :break) :eof)]