381 lines
12 KiB
Plaintext
381 lines
12 KiB
Plaintext
(comment
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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.
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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.
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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.
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Do I really need to optimize this? I don't think so: we can do that later. I could store various information on stacks.
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Alternately, returning data structures may well complicate things: KISS!
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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 `*`)
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)
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(defn pprint [x] (printf "%M" x))
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(os/cd "janet") ### XXX: to remove, repl only
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(import ./scanner :prefix "")
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(defn new-parser
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``
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Creates a new parser from a list of tokens. A parser has three fields in addition to `:tokens`:
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:i the index, in the list of tokens, of the current token
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:errors an array of errors, treated like a stack
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:captured an array of captures (tokens or arrays of tokens), treated like a stack.
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``
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[{:tokens tokens}]
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@{:tokens tokens :i 0 :errors @[] :captured @[]})
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(defn pop-to
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"Pops items from a stack until it contains `len` items. Returns the stack."
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[stack len]
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(assert (>= len 0))
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(while (< len (length stack)) (array/pop stack))
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stack)
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(defn popn
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"Pops n items from a stack. Returns the stack."
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[stack n]
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(loop [_ :range [0 n]] (array/pop stack))
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stack)
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(defn current "Returns the current token." [{:tokens tokens :i i}] (get tokens i))
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(defn previous "Returns the token before the current token." [{:tokens tokens :i i}] (get tokens (dec i)))
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(defn next "Returns the token after the current token." [{:tokens tokens :i i}] (get tokens (inc i)))
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(def add +) ### I `def` `+` later; stash this
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(defn advance
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"Advances the parser by `count`, or 1 if count is not supplied."
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[parser] (update parser :i inc))
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(defn stash
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"Stashes a parser state: captures the current index, error, and capture stacks."
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[{:i i :errors errs :captured cap}]
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{:i i :err-len (length errs) :cap-len (length cap)})
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(defn restore
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"Restores the parser to a stashed state: resets :i, pops any new errors and captures off their stacks."
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[parser state]
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(def {:i i :err-len err-len :cap-len cap-len} state)
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(def {:errors errors :captured captured} parser)
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(put parser :i i)
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(pop-to errors err-len)
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(pop-to captured cap-len)
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parser)
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(defn at "Returns the token at index i." [parser i] (get (get parser :tokens) i))
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(defn capture "Captures the last token." [parser] (update parser :captured array/push (previous parser)))
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(defn apply-keyword
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"Applies a keyword-based rule. Consumes the passing token."
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[kw parser]
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(def curr (current parser))
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(def type (get curr :type))
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(if (= kw type)
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(do
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(advance parser)
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true)
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nil))
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(defn apply-table
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"Applies a table-based rule."
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[rule parser]
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(def curr (current parser))
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(def rule-fn (get rule :rule))
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(rule-fn parser))
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(defn apply-rule
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"Applies a rule: if the rule passes, consume all passing tokens and return true. If the rule fails, do nothing, returning `nil`."
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[rule parser]
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(case (type rule)
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:keyword (apply-keyword rule parser)
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:table (apply-table rule parser)
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(error (string "unknown parser type: " (type rule)))))
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(defn name
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"Returns the name of a rule. Use this instead of (get rule :name), since bare keywords are also valid rules."
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[rule]
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(case (type rule)
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:keyword rule
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:table (rule :name)))
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(defn rename
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"Renames a rule. By convention, rule names are keywords."
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[rule name] (put rule :name name))
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(defn test
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"Tests a rule: returns whether a rule passes but does not consume any tokens."
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[rule parser]
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(def origin (stash parser))
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(def result (apply-rule rule parser))
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(restore parser origin)
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result)
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(defn !
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"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."
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[rule]
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@{:name (keyword (string "!" (name rule)))
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:rule (fn !* [parser]
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(def result (test rule parser))
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(if-not result
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(do (advance parser) true)
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nil))})
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(defn <-
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"Capture: if the rule matches, consumes the token and pushes it to the capture stack. If the rule does not match, does nothing."
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[rule]
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@{:name (keyword (string "<-" (name rule)))
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:rule (fn <-* [parser]
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(def origin (stash parser))
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(def result (apply-rule rule parser))
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(if result (capture parser))
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result)})
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(defn +
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"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."
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[& rules]
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@{:name (keyword (string/join (map name rules) "+"))
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:rule (fn +* [parser]
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(var passing nil)
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(def origin (stash parser))
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(loop [rule :in rules :while (not passing)]
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(restore parser origin)
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(set passing (apply-rule rule parser)))
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(if-not passing (restore parser origin))
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passing)})
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(defn unreachable [&] (error "reached the unreachable"))
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(defmacro declare [& names]
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(def bindings @[])
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(loop [name :in names]
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(def binding ~(var ,name @{:name ,(keyword name) :rule unreachable}))
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(array/push bindings binding))
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~(upscope ,;bindings))
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(defmacro defp [name rule]
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(if (dyn name)
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~(set ,name (put ,name :rule (,rule :rule)))
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~(var ,name (rename ,rule ,(keyword name)))))
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# If we wanted to be robust, we wouldn't hard-code this
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(defp stop (+ :newline :semicolon :break))
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(defn panic
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[rule &opt msg]
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@{:name (keyword (string "panic-" (name rule)))
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:rule (fn panic* [parser]
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(print "panicking!")
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(def origin (current parser))
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(var passing false)
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(def skipped @[])
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(while (not passing)
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(array/push skipped (current parser))
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(advance parser)
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(set passing (apply-rule rule parser)))
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(print "looped")
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(def the-error @{:type :error :token origin :msg msg :skipped skipped})
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(array/push (parser :errors) the-error)
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(array/push (parser :captured) the-error)
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true
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)})
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(defn panic
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"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."
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[parser expected]
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(print "panic! in the parser")
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(def origin (current parser))
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(var passing false)
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(def skipped @[])
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(while (not passing)
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(array/push skipped (current parser))
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(advance parser)
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(set passing (apply-rule rule parser)) ### compile error: unknown symbol rule
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(print "phew; I'm done panicking")
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(pprint (current parser))
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(def the-error {:type :error :expected expected :token origin :skipped skipped})
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(array/push (parser :errors) the-error)
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(array/push (parser :captured) the-error)
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(error parser)))
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(defn *
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"Sequences rules: matches if all rules are matched, in sequence."
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[& rules]
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@{:name (keyword (string/join (map name rules) "*"))
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:rule (fn ** [parser]
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(print "applying sequence")
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(var passing true)
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(def origin (stash parser))
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(pprint origin)
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(set failing nil) ### compile error: unknonw symbol failing
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(loop [rule :in rules :while passing]
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(def pass? (apply-rule rule parser))
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(when (not pass?)
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(set failing rule)
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(set passing false)))
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# this isn't the right thing to do: don't back out, panic!
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# (when (not passing) (restore parser origin))
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(if passing
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passing
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(panic parser (string "expected " (name failing)))))})
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## next problem: where do we back out to, and how?
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## 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`
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## maybe terms in a tuple, list, dict
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## 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
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## they're not all either any or some (empty data structures, but lines in blocks and scripts)
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## also: there's a finite number of possibilities for any of them:
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## another well-formed term, or the end of the item
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## consider:
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(comment
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(defp tuple-term (nonbinding (some separator)))
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(defp tuple-expr (order-1 (<- :lparen) (any separator) (any! tuple-term separator) (:rparen)))
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)
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## the tuple-term can be the anchor point
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## also, in this case, we panic until a *separator*, not a *terminator*
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## that suggests we need a panic-until parameter, rather than the hardcoded stop
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## is this right?
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(defn order-1 [& rules]
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@{:name (keyword (string/join (map name rules) "*"))
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:rule (fn order-1 [parser]
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(def result (test (first rules) parser))
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(if result
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(apply-rule (order-0 ;rules)) ### compile error: unknown symbol order-0
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nil))})
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(defn capture-group
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"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."
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[parser origin]
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(def from (get origin :cap-len))
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(def captured (get parser :captured))
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(def grouped (array/slice captured from -1))
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(pop-to captured from)
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(array/push captured grouped)
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captured)
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(defn &
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"Groups rules: pops all captured patterns and pushes them on the captured stack as a single array."
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[rule]
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@{:name (keyword (string "&" (name rule)))
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:rule (fn &* [parser]
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(def origin (stash parser))
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(def result (apply-rule rule parser))
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(if result
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(do
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(capture-group parser origin)
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true)
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(do
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(restore parser origin)
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nil)))})
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(defn fn-name
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"Returns the name of a function."
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[f]
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(def rep (string f))
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(string/slice rep 10 -2))
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(defn /
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"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."
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[rule f]
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@{:name (keyword (string (name rule) "/" (fn-name f)))
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:rule (fn /* [parser]
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(def origin (stash parser))
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(def captured (get parser :captured))
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(def result (apply-rule (& rule) parser))
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(if result
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(do
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(def grouped (array/pop captured))
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(def applied (f ;grouped))
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(array/push captured applied)
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true)
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(do
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(restore parser origin)
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nil)))})
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(defn any
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"Matches zero or more instances of a rule."
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[rule]
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@{:name (keyword (string "any-" (name rule)))
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:rule (fn any* [parser]
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(var result true)
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(while result
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(set result (apply-rule rule parser)))
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true)})
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(defn some
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"Matches one or more instances of a rule."
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[rule]
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@{:name (keyword (string "some-" (name rule)))
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:rule (fn some* [parser]
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(def origin (stash parser))
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(def result (apply-rule rule parser))
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(if result
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(do
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(apply-rule (any rule) parser)
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true)
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(do
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(restore parser origin)
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nil)))})
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(defn parse [tokens rule]
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(def parser (new-parser tokens))
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(try
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(do (apply-rule rule parser) parser)
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([err] err)))
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(upscope #XXX for repl use
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(defn literal->ast [token] {:type (get token :type) :data (get token :literal) :token token})
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(defn word->ast [token] {:type (get token :type) :data (get token :lexeme) :token token})
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(defn tuple->ast [origin & tokens] {:type :tuple :data tokens :token origin})
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(defn if->ast [origin & tokens] {:type :if :data tokens :token origin})
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(declare expression simple nonbinding)
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(defp separator (+ :newline :comma :break))
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(defp separators? (any (+ :newline :comma :break)))
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(defp terminator (some (+ :newline :semicolon :break)))
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(defp terminators? (any (+ :newline :semicolon :break)))
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(defp nls? (any :newline))
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(defp atom (/ (<- (+ :nil :true :false :number :keyword :string)) literal->ast))
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(defp word (/ (<- :word) word->ast))
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(defp tuple-term (* nonbinding separator))
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(defp tuple-literal (/ (* (<- :lparen) separators? (any tuple-term) :rparen) tuple->ast))
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(defp if-expr (/ (* (<- :if) simple nls? :then nonbinding nls? :else nonbinding) if->ast))
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# (defp root (<- (+ :word :keyword)))
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# (defp follow (<- (+ :keyword :arg-tuple)))
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# (defp synthetic (& (* root (some follow))))
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(defp simple (+ atom word tuple-literal))
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(defp nonbinding (+ atom word tuple-literal))
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(defp expression (+ atom word tuple-literal))
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(defp line (* expression (some terminator)))
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# (defp toplevel)
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(defp script (some line))
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(def source
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``
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if (:)foo then :bar else :baz
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``
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)
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(-> (scan source) (parse if-expr) pprint)
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)
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