From efffbafdba1dde0a954127b58936799d977d38ad Mon Sep 17 00:00:00 2001
From: Scott Richmond <kredati@users.noreply.github.com>
Date: Mon, 25 Mar 2024 16:04:54 -0400
Subject: [PATCH] Save some work.

---
 janet/myparser.janet   | 380 +++++++++++++++++++++++++++++++++++++++++
 janet/parser.janet     |   4 +-
 janet/peg-parser.janet | 104 +++++++++++
 janet/test.janet       |   7 +
 4 files changed, 494 insertions(+), 1 deletion(-)
 create mode 100644 janet/myparser.janet
 create mode 100644 janet/peg-parser.janet
 create mode 100644 janet/test.janet

diff --git a/janet/myparser.janet b/janet/myparser.janet
new file mode 100644
index 0000000..7ae9342
--- /dev/null
+++ b/janet/myparser.janet
@@ -0,0 +1,380 @@
+(comment
+So the thing here is that this is a much, much simpler version of the rather unweildy Clojure parser framework I wrote. This leans pretty hard on the Janet PEG framework, but is also bespoke for my purposes here.
+
+This lets me parse not raw text, but scanned tokens, which makes parsing a much easier lift. Also, it lets me do things like insert :break tokens, which really helps manage collection types and blocks.
+
+At current, I do need to shift to returning a data structure rather than `nil`s and `true`s. That way, I can advance the parser by a certain amount, however much a passing test-rule would consume.
+
+Do I really need to optimize this? I don't think so: we can do that later. I could store various information on stacks.
+
+Alternately, returning data structures may well complicate things: KISS!
+
+The idea, however, is that Jesus: we must not have test-rule and apply-rule: combinators without a fixed advance amount can't work that way. So we have only `apply-rule`, which `advance`s the parser by however much should be consumed. BUT! We can always, and ought wherever we might, stash the origin index and roll back any changes (i.e. in `!` and `*`)
+
+)
+
+(defn pprint [x] (printf "%M" x))
+
+(os/cd "janet") ### XXX: to remove, repl only
+(import ./scanner :prefix "")
+
+(defn new-parser 
+	``
+	Creates a new parser from a list of tokens. A parser has three fields in addition to `:tokens`:
+	:i the index, in the list of tokens, of the current token
+	:errors an array of errors, treated like a stack
+	:captured an array of captures (tokens or arrays of tokens), treated like a stack.
+	``
+	[{:tokens tokens}]
+		@{:tokens tokens :i 0 :errors @[] :captured @[]})
+
+(defn pop-to 
+	"Pops items from a stack until it contains `len` items. Returns the stack."
+	[stack len]
+		(assert (>= len 0))
+		(while (< len (length stack)) (array/pop stack))
+		stack)
+
+(defn popn 
+	"Pops n items from a stack. Returns the stack."
+	[stack n]
+		(loop [_ :range [0 n]] (array/pop stack))
+		stack)
+
+(defn current "Returns the current token." [{:tokens tokens :i i}] (get tokens i))
+
+(defn previous "Returns the token before the current token." [{:tokens tokens :i i}] (get tokens (dec i)))
+
+(defn next "Returns the token after the current token." [{:tokens tokens :i i}] (get tokens (inc i)))
+
+(def add +) ### I `def` `+` later; stash this
+
+(defn advance 
+	"Advances the parser by `count`, or 1 if count is not supplied."
+	[parser] (update parser :i inc))
+
+(defn stash 
+	"Stashes a parser state: captures the current index, error, and capture stacks."
+	[{:i i :errors errs :captured cap}]
+		{:i i :err-len (length errs) :cap-len (length cap)})
+
+(defn restore 
+	"Restores the parser to a stashed state: resets :i, pops any new errors and captures off their stacks."
+	[parser state]
+		(def {:i i :err-len err-len :cap-len cap-len} state)
+		(def {:errors errors :captured captured} parser)
+		(put parser :i i)
+		(pop-to errors err-len)
+		(pop-to captured cap-len)
+		parser)
+
+(defn at "Returns the token at index i." [parser i] (get (get parser :tokens) i))
+
+(defn capture "Captures the last token." [parser] (update parser :captured array/push (previous parser)))
+
+(defn apply-keyword 
+	"Applies a keyword-based rule. Consumes the passing token."
+	[kw parser]
+	(def curr (current parser))
+	(def type (get curr :type))
+	(if (= kw type)
+		(do
+			(advance parser)
+			true)
+		nil))
+
+(defn apply-table 
+	"Applies a struct-based rule."
+	[rule parser]
+	(def curr (current parser))
+	(def rule-fn (get rule :rule))
+	(rule-fn parser))
+
+(defn apply-rule 
+	"Applies a rule: if the rule passes, consume all passing tokens and return true. If the rule fails, do nothing, returning `nil`."
+	[rule parser]
+	(case (type rule)
+		:keyword (apply-keyword rule parser)
+		:table (apply-table rule parser)
+		(error (string "unknown parser type: " (type rule)))))
+
+(defn name 
+	"Returns the name of a rule. Use this instead of (get rule :name), since bare keywords are also valid rules."
+	[rule]
+	(case (type rule)
+		:keyword rule
+		:table (rule :name)))
+
+(defn rename 
+	"Renames a rule. By convention, rule names are keywords."
+	[rule name] (put rule :name name))
+
+(defn test 
+	"Tests a rule: returns whether a rule passes but does not consume any tokens."
+	[rule parser]
+	(def origin (stash parser))
+	(def result (apply-rule rule parser))
+	(restore parser origin)
+	result)
+
+(defn ! 
+	"Not: negates a rule. If the rule passes, does nothing, returns `nil`. If the rule fails, advances the parser a single token, returns true. Works well only for single token rules."
+	[rule]
+	@{:name (keyword (string "!" (name rule)))
+		:rule (fn !* [parser]
+			(def result (test rule parser))
+			(if-not result
+				(do (advance parser) true)
+				nil))})
+
+(defn <- 
+	"Capture: if the rule matches, consumes the token and pushes it to the capture stack. If the rule does not match, does nothing."
+	[rule]
+	@{:name (keyword (string "<-" (name rule)))
+		:rule (fn <-* [parser]
+			(def origin (stash parser))
+			(def result (apply-rule rule parser))
+			(if result (capture parser))
+			result)})
+
+(defn + 
+	"Choose a rule: matches if any one of the rules is matched. Order matters: rules are evaluated in order. It's useful to put any errors last."
+	[& rules]
+	@{:name (keyword (string/join (map name rules) "+"))
+		:rule (fn +* [parser]
+			(var passing nil)
+			(def origin (stash parser))
+			(loop [rule :in rules :while (not passing)]
+				(restore parser origin)
+				(set passing (apply-rule rule parser)))
+			(if-not passing (restore parser origin))
+			passing)})
+
+(defn unreachable [&] (error "reached the unreachable"))
+
+(defmacro declare [& names]
+	(def bindings @[])
+	(loop [name :in names]
+		(def binding ~(var ,name @{:name ,(keyword name) :rule unreachable}))
+		(array/push bindings binding))
+	~(upscope ,;bindings))
+
+(defmacro defp [name rule]
+	(if (dyn name)
+		~(set ,name (put ,name :rule (,rule :rule)))
+		~(var ,name (rename ,rule ,(keyword name)))))
+
+# If we wanted to be robust, we wouldn't hard-code this
+(defp stop (+ :newline :semicolon :break))
+
+(defn panic
+	[rule &opt msg]
+	@{:name (keyword (string "panic-" (name rule)))
+		:rule (fn panic* [parser]
+			(print "panicking!")
+			(def origin (current parser))
+			(var passing false)
+			(def skipped @[])
+			(while (not passing)
+				(array/push skipped (current parser))
+				(advance parser)
+				(set passing (apply-rule rule parser)))
+			(print "looped")
+			(def the-error @{:type :error :token origin :msg msg :skipped skipped})
+			(array/push (parser :errors) the-error)
+			(array/push (parser :captured) the-error)
+			true
+		)})
+
+(defn panic 
+	"Panics the parser, consuming all tokens until the rule matches (including the match). It also adds an error node to both the capture and the error stacks."
+	[parser expected]
+		(print "panic! in the parser")
+		(def origin (current parser))
+		(var passing false)
+		(def skipped @[])
+		(while (not passing)
+			(array/push skipped (current parser))
+			(advance parser)
+			(set passing (apply-rule rule parser))
+		(print "phew; I'm done panicking")
+		(pprint (current parser))
+		(def the-error {:type :error :expected expected :token origin :skipped skipped})
+		(array/push (parser :errors) the-error)
+		(array/push (parser :captured) the-error)
+		(error parser)))
+
+(defn * 
+	"Sequences rules: matches if all rules are matched, in sequence."
+	[& rules]
+	@{:name (keyword (string/join (map name rules) "*"))
+		:rule (fn ** [parser]
+			(print "applying sequence")
+			(var passing true)
+			(def origin (stash parser))
+			(pprint origin)
+			(set failing nil)
+			(loop [rule :in rules :while passing]
+				(def pass? (apply-rule rule parser))
+				(when (not pass?) 
+					(set failing rule)
+					(set passing false)))
+			# this isn't the right thing to do: don't back out, panic!
+			# (when (not passing) (restore parser origin))
+			(if passing
+				passing
+				(panic parser (string "expected " (name failing)))))})
+## next problem: where do we back out to, and how?
+## the answer: an "anchor" point, where we `(try) something, and if it panics, start up with another line; in a block it will be line; in a script it will be toplevel`
+## maybe terms in a tuple, list, dict
+## it seems noteworthy that the things we want to return to are all either "any" or "some", and all either end with a newline or a break
+## they're not all either any or some (empty data structures, but lines in blocks and scripts)
+## also: there's a finite number of possibilities for any of them:
+## another well-formed term, or the end of the item
+## consider:
+(comment
+(defp tuple-term (nonbinding (some separator)))
+(defp tuple-expr (order-1 (<- :lparen) (any separator) (any! tuple-term separator) (:rparen)))
+)
+## the tuple-term can be the anchor point
+## also, in this case, we panic until a *separator*, not a *terminator*
+## that suggests we need a panic-until parameter, rather than the hardcoded stop
+## is this right?
+
+
+(defn order-1 [& rules]
+	@{:name (keyword (string/join (map name rules) "*"))
+		:rule (fn order-1 [parser]
+			(def result (test (first rules) parser))
+			(if result
+				(apply-rule (order-0 ;rules))
+				nil))})
+
+(defn capture-group
+	"Takes a parser and an origin state: takes everything captured since the origin, gathers it up in a single array, pops it all off the capture stack, and pushes the gathered captures back on the stack."
+	[parser origin]
+		(def from (get origin :cap-len))
+		(def captured (get parser :captured))
+		(def grouped (array/slice captured from -1))
+		(pop-to captured from)
+		(array/push captured grouped)
+		captured)
+
+(defn & 
+	"Groups rules: pops all captured patterns and pushes them on the captured stack as a single array."
+	[rule]
+	@{:name (keyword (string "&" (name rule)))
+		:rule (fn &* [parser]
+			(def origin (stash parser))
+			(def result (apply-rule rule parser))
+			(if result
+				(do
+					(capture-group parser origin)
+					true)
+				(do
+					(restore parser origin)
+					nil)))})
+
+(defn fn-name 
+	"Returns the name of a function."
+	[f]
+		(def rep (string f))
+		(string/slice rep 10 -2))
+
+(defn / 
+	"Substitution: takes a rule and a function, and applies the function to any captures arising from the rule; the captures are individual parameters to the function."
+	[rule f]
+	@{:name (keyword (string (name rule) "/" (fn-name f)))
+		:rule (fn /* [parser]
+			(def origin (stash parser))
+			(def captured (get parser :captured))
+			(def result (apply-rule (& rule) parser))
+			(if result
+				(do
+					(def grouped (array/pop captured))
+					(def applied (f ;grouped))
+					(array/push captured applied)
+					true)
+				(do
+					(restore parser origin)
+					nil)))})
+
+(defn any 
+	"Matches zero or more instances of a rule."
+	[rule] 
+	@{:name (keyword (string "any-" (name rule)))
+		:rule (fn any* [parser]
+			(var result true)
+			(while result
+				(set result (apply-rule rule parser)))
+			true)})
+
+(defn some 
+	"Matches one or more instances of a rule."
+	[rule]
+	@{:name (keyword (string "some-" (name rule)))
+		:rule (fn some* [parser]
+			(def origin (stash parser))
+			(def result (apply-rule rule parser))
+			(if result
+				(do
+					(apply-rule (any rule) parser)
+					true)
+				(do
+					(restore parser origin)
+					nil)))})
+
+(defn parse [tokens rule]
+	(def parser (new-parser tokens))
+	(try 
+		(do (apply-rule rule parser) parser)
+		([err] err))
+
+(upscope
+
+(defn literal->ast [token] {:type (get token :type) :data (get token :literal) :token token})
+
+(defn word->ast [token] {:type (get token :type) :data (get token :lexeme) :token token})
+
+(defn tuple->ast [origin & tokens] {:type :tuple :data tokens :token origin})
+
+(defn if->ast [origin & tokens] {:type :if :data tokens :token origin})
+
+(declare expression simple nonbinding)
+
+(defp separator (+ :newline :comma :break))
+(defp separators? (any (+ :newline :comma :break)))
+(defp terminator (some (+ :newline :semicolon :break)))
+(defp terminators? (any (+ :newline :semicolon :break)))
+(defp nls? (any :newline))
+
+(defp atom (/ (<- (+ :nil :true :false :number :keyword :string)) literal->ast))
+(defp word (/ (<- :word) word->ast))
+
+(defp tuple-term (* nonbinding separator))
+(defp tuple-literal (/ (* (<- :lparen) separators? (any tuple-term) :rparen) tuple->ast))
+
+(defp if-expr (/ (* (<- :if) simple nls? :then nonbinding nls? :else nonbinding) if->ast))
+
+# (defp root (<- (+ :word :keyword)))
+# (defp follow (<- (+ :keyword :arg-tuple)))
+# (defp synthetic (& (* root (some follow))))
+
+(defp simple (+ atom word tuple-literal))
+(defp nonbinding (+ atom word tuple-literal))
+(defp expression (+ atom word tuple-literal))
+(defp line (* expression (some terminator)))
+# (defp toplevel)
+(defp script (some line))
+
+(def source
+``
+if (:)foo then :bar else :baz
+
+``
+)
+
+(-> (scan source) (parse if-expr) pprint)
+)
+
+
diff --git a/janet/parser.janet b/janet/parser.janet
index 4f35553..32c428c 100644
--- a/janet/parser.janet
+++ b/janet/parser.janet
@@ -1,4 +1,6 @@
-### in repl, make sure to (os/cwd) into the janet dir
+### in repl, make sure to (os/cd) into the janet dir
+# (os/cd "janet")
+
 (import ./clj-loop :prefix "")
 
 (defn ? [val default] (if (nil? val) default val))
diff --git a/janet/peg-parser.janet b/janet/peg-parser.janet
new file mode 100644
index 0000000..7241178
--- /dev/null
+++ b/janet/peg-parser.janet
@@ -0,0 +1,104 @@
+(defn ->kw [kw-str]
+	(keyword (slice kw-str 1)))
+
+(defn word [str] [:word str])
+
+(defn num [num] [:number (scan-number num)])
+
+(defn kw [_ kw] [:keyword (->kw kw)])
+
+(defn str [str] [:string str])
+
+(defn bool [bool] (if (= bool "true") [:boolean true] [:boolean false]))
+
+(defn nill [_] [:nil nil])
+
+(defn not-empty? [x] (not (empty? x)))
+
+(defn ifl [args] [:if ;args])
+
+(defn letl [args] [:let ;args])
+
+(defn block [args] [:block args])
+
+(def errors @[])
+
+(defn ? [x default] (if (nil? x) default x))
+
+(defn panic [& args]
+	(def info (filter |(not= "" $) args))
+	(def [msg line col source] info)
+	(def error {:msg msg :line line :col col :source (? source "")})	
+	(array/push errors error)
+	[:error error]
+)
+
+(do
+(def ludus-grammar
+	~{:nil (cmt (<- "nil") ,nill)
+		:true (cmt (<- "true") ,bool)
+		:false (cmt (<- "false") ,bool)
+		:comment (* "&" (any (if-not (+ "\n" -1) 1)))
+		:wordchars (+ :w (set "_-/*?!"))
+		:reserved (+ "if" "then" "else" "let")
+		:word (cmt (<- (if-not :reserved (* (range "az") (any :wordchars)))) ,word)
+		:keyword (cmt (<- (* ":" :word)) ,kw)
+		:hex (range "09" "af" "AF")
+		:escape (* "\\" (+ (set `"'0?\abefnrtvz`)
+                       (* "x" :hex :hex)
+                       (* "u" [4 :hex])
+                       (* "U" [6 :hex])
+                       (error (constant "bad escape"))))
+		:string (cmt (* "\"" (<- (any (+ :escape (if-not "\"" 1)))) "\"") ,str)
+		:int (* (? "-") (range "19") (any (+ "_" (range "09"))))
+		:float (* (? "-") (+ :int "0") "." (any (+ "_" (range "09"))))
+		:zero "0"
+		:number (cmt (<- (+ :float :int :zero)) ,num)
+		:comment (* "&" (any (if-not (+ "\n" -1) 1)))
+		:atom (+ :nil :true :false :keyword :number :word)
+		:newline "\n"
+		:terminator (* (any :ws) (some (+ :newline ";")))
+		:separator (* (any :ws) (some (+ :newline ",")))
+		:ws (any (+ :comment (set " \t")))
+		:simple (+ :atom :string :word (* (constant "expected simple" :err-msg) :panic))
+		:then (+ (* (+ (some :ws) (any :newline)) (any :ws) "then" (some :ws)) (* (constant "expected then" :err-msg) :panic))
+		:else (+ (* (+ (some :ws) (any :newline)) (any :ws) "else" (some :ws)) (* (constant "expected else" :err-msg) :panic))
+		:panic (cmt (* (<- (-> :err-msg)) (<- (line)) (<- (column)) (<- (* (any (if-not (+ "\n" -1) 1))))) ,panic)
+		:non-binding (+ :atom :word :string :if :block 
+			(* (constant "expected non-binding" :err-msg) :panic))
+		:tuple-term (* :number (some :separator))
+		:tuple (* "(" (any :separator) (any :tuple-term) ")")
+		:block (cmt (group (* "{" (some :line) (? :expression) "}")) ,block)
+		:if (cmt (group (* "if" (some :ws) :simple :then :non-binding :else :non-binding)) ,ifl)
+		:pattern (+ :atom :string (* (constant "expected pattern") :panic))
+		:equals (* (any :ws) "=" (any :ws))
+		:let (cmt (group (* "let" (some :ws) :pattern :equals :non-binding)) ,letl)
+		:expression (+ :atom :string :block :if :let
+			(* (constant "expected expression" :err-msg) :panic))
+		:empty (* :ws :terminator)
+		:line (* :ws :expression :ws :terminator)
+		:main :tuple})
+		
+(def simple-tuple ~{
+	:value (<- (range "az"))
+	:separator (+ "," "\n")
+	:ws (any (set " \t"))
+	:term (* :ws :value :ws :separator)
+	:tuple (group (* "(" (any :term) (? :value) :ws ")"))
+	:main :tuple
+})
+
+
+# :empty/:line/:block are still giving me grief
+# also, somehow line & column numbers ar
+(def source
+``
+(   a, b  ,c,d   )
+``
+)
+
+
+(peg/match simple-tuple source)
+)
+
+
diff --git a/janet/test.janet b/janet/test.janet
new file mode 100644
index 0000000..4057c58
--- /dev/null
+++ b/janet/test.janet
@@ -0,0 +1,7 @@
+(def myodd? nil)
+
+(defn myeven? [x] (if (= 0 x) true (myodd? (dec x))))
+
+(defn myodd? [x] (if (= 0 x) false (myeven? (dec x))))
+
+(myeven? 2)