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improve error for parsing from a nonexistent lhs #128

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improve error for parsing from a nonexistent lhs #128

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5 changes: 5 additions & 0 deletions src/instaparse/gll.clj
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Original file line number Diff line number Diff line change
Expand Up @@ -872,6 +872,11 @@
;; Parsing functions

(defn start-parser [tramp parser partial?]
(let [starting-prod (:keyword parser)
known-productions (into #{} (map first (:grammar tramp)))]
(when (not (known-productions starting-prod))
(throw (IllegalArgumentException.
(str "Nonexistent starting production: " starting-prod)))))
(if partial?
(push-listener tramp [0 parser] (TopListener tramp))
(push-full-listener tramp [0 parser] (TopListener tramp))))
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9 changes: 9 additions & 0 deletions test/instaparse/core_test.clj
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Expand Up @@ -684,6 +684,15 @@
15
))

(deftest error-nonexistent-starting-production
(let [parser (insta/parser "cat = 'mjau'")]
(is (thrown-with-msg?
IllegalArgumentException
#"Nonexistent starting production: :dog"
(insta/parse parser "mjau" :start :dog)))
(is (= [:cat "mjau"]
(insta/parse parser "mjau" :start :cat)))))

(defn round-trip [parser]
(insta/parser (prn-str parser)))

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