Hi,
I'm trying to write a small parser using DCG, but when I use the code
below
-------------- parser.clj -----------------------
(ns compiler.parser
(:refer-clojure :exclude [==])
(:use [clojure.core.logic]
[clojure.core.logic.dcg] )
)
(def-->e token [tg x]
([_ ?tk] [?tk]
(!dcg
(project [?tk]
(== (= (?tk :tag) tg) true)))))
(declare expr1 term term term1 factor)
(def-->e expr [e]
([?e1] (fresh [t] (term t) (expr1 t ?e1))))
(def-->e expr1 [t e]
([t1 ?e1] (fresh [tk t2]
(token '+ tk) (term t2) (expr1 {:binop '+ t1 t2} ?e1)))
([_ t] []))
(def-->e term [t]
([?t1] (fresh [f] (factor f) (term1 f ?t1))))
(def-->e term1 [f t]
([f1 ?t1] (fresh [tk f2]
(token '* tk) (factor f2) (term1 {:binop '* f1 f2} ?t1)))
([_ f] []))
(def-->e factor [tree]
([?tk] (token 'id ?tk))
([?tk] (token 'int ?tk))
([?tk] (token 'real ?tk)))
(def tokens1 [{:tag 'int, :value 1, :start {:line 1, :col 1}}
{:tag '+, :start {:line 1, :col 2}}
{:tag 'int, :value 2, :start {:line 1, :col 3}} ])
(def tokens2 [{:tag 'int, :value 1, :start {:line 1, :col 1}}
{:tag '*, :start {:line 1, :col 2}}
{:tag 'int, :value 2, :start {:line 1, :col 3}} ])
(defn tests [num]
(let [tokens (case num
1 tokens1
2 tokens2)]
(run 1 [tree] (expr tree tokens []))))
--------------------------------------------------
I get these answers in Clojure:
compiler.parser=> (tests 1)
({:binop +, <lvar:t1_5036> {:start {:col 3, :line 1}, :value 2, :tag int}})
compiler.parser=> (tests 2)
({:binop *, <lvar:f1_5079> {:start {:col 3, :line 1}, :value 2, :tag int}})
The first argument is a logical variable not instanced and what I'm
expecting is:
compiler.parser=> (tests 1)
({:binop + {:tag 'int, :value 1, :start {:line 1, :col 1}}
{:start {:col 3, :line 1}, :value 2, :tag int}})
compiler.parser=> (tests 2)
({:binop * {:tag 'int, :value 1, :start {:line 1, :col 1}}
{:start {:col 3, :line 1}, :value 2, :tag int}})
What am I doing wrong?
Thanks in advance for any answer.
Regards,
Alex
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