128 lines
3.7 KiB
Clojure
128 lines
3.7 KiB
Clojure
(ns ^{:doc "A parser for SQL: simplify/normalise a parse tree."
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:author "Simon Brooke"}
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squirrel-parse.simplify
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(:require [clojure.string :refer [join split trim triml upper-case]]))
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;;;
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;;;; squirrel-parse.simplify: simplify/normalise a parse tree.
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;;;;
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;;;; This program is free software; you can redistribute it and/or
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;;;; modify it under the terms of the GNU General Public License
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;;;; as published by the Free Software Foundation; either version 2
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;;;; of the License, or (at your option) any later version.
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;;;;
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;;;; This program is distributed in the hope that it will be useful,
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;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;;; GNU General Public License for more details.
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;;;;
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;;;; You should have received a copy of the GNU General Public License
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;;;; along with this program; if not, write to the Free Software
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;;;; Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
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;;;; USA.
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;;;;
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;;;; Copyright (C) 2018 Simon Brooke
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;;;;
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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(declare in-simplify)
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(defn ignorable?
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"True if `x` is something which just clutters up the parse tree."
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[x]
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(and
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(coll? x)(contains? #{:COMMENT
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:LPAR
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:OPT-KW-DATA
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:OPT-SPACE
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:QUOTE-MK
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:RPAR
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:SPACE
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:TERMINATOR} (first x))))
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(defn simplify-second-of-two
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"There are a number of possible simplifications such that if the `tree` has
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only two elements, the second is semantically sufficient."
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[tree]
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(if
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(and (= (count tree) 2) (coll? (nth tree 1)))
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(in-simplify (nth tree 1))
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tree))
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(defn simplify-second-if-not-empty
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"Like `simplify-second-of-two`, but returns nil if there is no second element
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of `tree`."
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[tree]
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(if
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(= (count tree) 1)
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nil
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(simplify-second-of-two tree)))
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(defn remove-recursive
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"Return a collection like this `collection` from which items which are matched
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by this `predicate` have been removed at all levels."
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[predicate collection]
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(map
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#(if
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(coll? %)
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(remove-recursive predicate %)
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%)
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(remove predicate collection)))
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(defn- in-simplify
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"Simplify/canonicalise this `tree`, presumed already to have had ignorables
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removed. Opportunistically replace complex fragments with
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semantically identical simpler fragments"
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[tree]
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(if
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(coll? tree)
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(case (first tree)
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(:STATEMENTS) (remove nil? (map in-simplify (rest tree)))
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(:EXISTENCE
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:PERMANENCE) (simplify-second-if-not-empty tree)
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(:ALTER-COL-SPEC
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:ALTER-SEQ-ELEMENT
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:ALTER-STMT
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:ALTER-TABLE-ELEMENT
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:CREATE-STMT
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:EXPRESSION
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:MATCH-TYPE
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:ONLY
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:OPT-KW-SCHEMA
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:PERMISSION
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:PERMISSIONS-STMT
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:REF-DIRECTIVE
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:RO-BYPASSRLS
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:RO-CREATEDB
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:RO-CREATEROLE
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:RO-INHERIT
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:RO-LOGIN
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:RO-REPLIC
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:RO-SUPERUSER
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:ROLE-OPTION
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:SEQ-SPEC-ELEMENT
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:STATEMENT
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:TABLE-SPEC-ELEMENT
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:TC-ELEMENT
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:VALUE) (simplify-second-of-two tree)
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(:PERMISSION-COMMA
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:TABLE-SPEC-ELT-COMMA) (in-simplify (nth tree 1))
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(:ROLE) (first tree)
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(remove nil? (map in-simplify tree)))
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tree))
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(defn simplify
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"Simplify/canonicalise this `tree`. Opportunistically replace complex fragments with
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semantically identical simpler fragments"
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[parse-tree]
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(in-simplify (remove-recursive ignorable? parse-tree)))
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