get when expressions worked out

janet/recursive.janet

@@ -22,7 +22,9 @@
   ~(set ,name (defn ,name ,;forms)))
 
 ### Next: a data structure for a parser
-(defn- new-parser [tokens]
+(defn- new-parser 
+ "Creates a new parser data structure to pass around"
+ [tokens]
  @{
   :tokens (tokens :tokens)
   :ast @[]
@@ -31,42 +33,63 @@
  })
 
 ### and some helper functions for interfacing with that data structure
-(defn- current [parser] 
- (def curr (get (parser :tokens) (parser :current)))
- (if (not curr)
-  (error "no more tokens")
-  curr))
+(defn- current 
+ "Returns the current token of a parser. If the parser is at the last token, keeps returning the last token."
+ [parser] 
+ (def tokens (parser :tokens))
+ (get tokens (parser :current) (last tokens)))
 
-(defn- peek [parser] (get (parser :tokens) (inc (parser :current))))
+(defn- peek 
+ "Returns the next token of the parser. If the parser is at the last token, keeps returning the last token." 
+ [parser] 
+ (def tokens (parser :tokens))
+ (get tokens (inc (parser :current)) (last tokens)))
 
-(defn- advance [parser] (update parser :current inc))
+(defn- advance 
+ "Advances the parser by a token" 
+ [parser] 
+ (update parser :current inc))
 
-(defn- type [token] (get token :type))
+(defn- type 
+ "Returns the type of a token" 
+ [token] 
+ (get token :type))
 
-(defn- check [parser type]
+(defn- check 
+ "Returns true if the parser's current token is one of the passed types"
+ [parser type & types]
+ (def accepts [type ;types])
  (def current-type (-> parser current (get :type)))
- (= type current-type))
+ (has-value? accepts current-type))
 
 ### Parsing functions
 # forward declarations
 (declare simple nonbinding expr toplevel synthetic)
 
 # errors
+# terminators are what terminate expressions
 (def terminators [:break :newline :semicolon :eof])
 
-(defn- terminates? [parser]
+(defn- terminates? 
+ "Returns true if the current token in the parser is a terminator"
+ [parser]
  (def curr (current parser))
  (def ttype (type curr))
  (has-value? terminators ttype))
 
+# breakers are what terminate panics
 (def breaking [:break :newline :semicolon :comma :eof :then :else])
 
-(defn- breaks? [parser]
+(defn- breaks? 
+ "Returns true if the current token in the parser should break a panic"
+ [parser]
  (def curr (current parser))
  (def ttype (type curr))
  (has-value? breaking ttype))
 
-(defn- panic [parser message]
+(defn- panic 
+ "Panics the parser: starts skipping tokens until a breaking token is encountered. Adds the error to the parser's errors array, and also errors out."
+ [parser message]
  (print "Panic in the parser: " message)
  (def origin (current parser))
  (advance parser)
@@ -79,18 +102,38 @@
  (update parser :errors array/push err)
  (error err))
 
-(defn- expected [parser ttype]
- (panic parser (string "expected " ttype ", got " (-> parser current type))))
+(defn- expected 
+ "Panics the parser with a message: expected {type} got ..."
+ [parser ttype & ttypes]
+ (def expected (map string [ttype ;ttypes]))
+ (def type-msg (string/join expected " | "))
+ (panic parser (string "expected {" type-msg "}, got " (-> parser current type))))
 
-(defn- expect [parser type]
- (if-not (check parser type) (expected parser type)))
+(defn- expect 
+ "Panics if the parser's current token is not of type; otherwise does nothing & returns nil"
+ [parser type & types]
+ (if-not (check parser type ;types) (expected parser type ;types)))
 
-(defn- expect-ret [parser type]
+(defn- expect-ret 
+ "Same as expect, but captures the error, returning it as a value"
+ [parser type]
  (try (expect parser type) ([e] e)))
 
-(defn- capture [parse-fn parser]
+(defn- capture 
+ "Applies the parse function to the parser, returning the parsed AST. If there is a panic, captures the panic and returns it as a value."
+ [parse-fn parser]
  (try (parse-fn parser) ([e] e)))
 
+(defn- accept-one
+ "Accepts a single token of passed type, advancing the parser if a match, doing nothing if not."
+ [parser type]
+ (if (check parser type) (advance parser)))
+
+(defn- accept-many
+ "Accepts any number of tokens of a passed type, advancing the parser on match until there are no more matches. Does nothing on no match."
+ [parser type]
+ (while (check parser type) (advance parser)))
+
 # atoms
 (defn- bool [parser]
  (expect parser :bool)
@@ -268,19 +311,59 @@
  ast)
 
 ### conditional forms
+# if {simple} then {nonbinding} else {nonbinding}
 (defn- iff [parser]
  (def ast {:type :if :data @[] :token (current parser)})
  (advance parser) #consume the if
  (array/push (ast :data) (capture simple parser))
- (when-let [err (expect-ret parser :then)] (array/push (ast :data) err))
- (advance parser)
+ (accept-many parser :newline)
+ (if-let [err (expect-ret parser :then)] 
+  (array/push (ast :data) err) 
+  (advance parser))
  (array/push (ast :data) (capture nonbinding parser))
- (when-let [err (expect-ret parser :else)] (array/push (ast :data) err))
- (advance parser)
+ (accept-many parser :newline)
+ (if-let [err (expect-ret parser :else)] 
+  (array/push (ast :data) err)
+  (advance parser))
  (array/push (ast :data) (capture nonbinding parser))
  ast)
 
-(defn- condd [parser])
+
+(defn- terminator [parser]
+ (if-not (terminates? parser) (panic parser "expected terminator"))
+ (advance parser)
+ (while (terminates? parser) (advance parser)))
+
+# {simple} -> {nonbinding} {terminator}
+(defn- when-clause [parser]
+ (def clause @[])
+ (print "parsing lhs: " (-> parser current type))
+ (array/push clause (capture simple parser))
+ (print "parsing arrow")
+ (if-let [err (expect-ret parser :arrow)] 
+  (array/push clause err)
+  (advance parser))
+ (print "accepting newlines")
+ (accept-many parser :newline)
+ (print "parsing rhs")
+ (array/push clause (nonbinding parser))
+ (print "parsing terminator")
+ (try (terminator parser) ([e] (array/push clause e)))
+ clause)
+
+(defn- whenn [parser]
+ (def ast {:type :when :data @[] :origin (current parser)})
+ (advance parser) # consume cond
+ (if-let [err (expect-ret parser :lbrace)]
+  (do
+   (array/push (ast :data) err)
+   (break ast))
+  (advance parser))
+ (accept-many parser :newline)
+ (while (not (check parser :rbrace :eof))
+  (array/push (ast :data) (capture when-clause parser)))
+ (advance parser)
+ ast)
 
 (defn- match [parser])
 
@@ -348,7 +431,7 @@
 
   # conditional forms
   :if (iff parser)
-  :cond (unreachable)
+  :when (whenn parser)
   :match (unreachable)
   :with (unreachable)
 
@@ -368,9 +451,9 @@
 (defrec expr [parser]
  (def curr (current parser))
  (case (type curr)
-  :let nil
-  :fn nil
-  :ref nil
+  :let (unreachable)
+  :fn (unreachable)
+  :ref (unreachable)
   :nil (nill parser)
   :true (bool parser)
   :false (bool parser)
@@ -383,7 +466,7 @@
   :startset (sett parser)
   :word (word parser)
   :if (iff parser)
-  :cond (unreachable)
+  :when (whenn parser)
   :match (unreachable)
   :with (unreachable)
   :do (unreachable)
@@ -393,16 +476,16 @@
 )
 
 (defrec toplevel [parser]
- (def curr (current parser))
+ (def when (current parser))
  (case (type curr)
-  :pkg nil
-  :ns nil
-  :test nil
-  :import nil
-  :use nil
-  :let nil
-  :fn nil
-  :ref nil
+  :pkg (unreachable)
+  :ns (unreachable)
+  :test (unreachable)
+  :import (unreachable)
+  :use (unreachable)
+  :let (unreachable)
+  :fn (unreachable)
+  :ref (unreachable)
   :nil (nill parser)
   :true (bool parser)
   :false (bool parser)
@@ -415,7 +498,7 @@
   :startset (sett parser)
   :word (word parser)
   :if (iff parser)
-  :cond (unreachable)
+  :when (whenn parser)
   :match (unreachable)
   :with (unreachable)
   :do (unreachable)
@@ -424,14 +507,17 @@
  )
 )
 
-(os/cd "janet") # For repl to do relative imports
+(os/cd "janet") # when repl to do relative imports
 (import ./scanner :as s)
 (do
 #(comment
-(def source "if foo then else baz")
+(def source "when {
+foo -> bar
+}
+")
 (def scanned (s/scan source))
 (def a-parser (new-parser scanned))
-(def parsed (nonbinding a-parser))
+(def parsed (whenn a-parser))
 (-> parsed)
 )