284 lines
15 KiB
Fennel
284 lines
15 KiB
Fennel
; sqlog, a datalog-like system built on sqlite
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; may not actually have the full power of datalog OR the full power of sqlite
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; datalog has a database of facts, and rules. facts are represented in sqlite directly as tables.
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; rules are used by the sqlog engine when generating queries; typically they take the form
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; of subqueries used in the WITH RECURSIVE clause.
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; It would be possible to store them as views, but the view would need to be regenerated from
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; its base rules anytime there is a change, so sqlog needs to know about them no matter what.
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; Making sqlog manage them in-memory also allows us to use it to query arbitrary sqlite databases.
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; Ideally we would persist rules as JSON in a special table; maybe sqlog_rules?
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(local Compiler {})
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; Generating SQL from Datalog should not be too complex, but it pays to start with the simplest
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; case and build up from there.
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; simple queries:
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; [p x y] -> SELECT p.c1 AS x, p.c2 AS y FROM p
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; [p 1 y] -> SELECT p.c2 AS y FROM p WHERE p.c1 = 1
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; [q x] [p x 1] -> SELECT q.c1 AS x FROM q JOIN p WHERE p.c1 = q.c1 AND p.c2 = 1
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; [p 1 2] -> SELECT true FROM p WHERE p.c1 = 1 AND p.c2 = 2
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; [p 1 x] [p x 2] -> SELECT t1.c2 AS x FROM p AS t1 JOIN p AS t2 WHERE t1.c1 = 1 AND t1.c2 = t2.c1 AND t2.c2 = 2
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; queries using rules:
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; ([ancestor x y] [parent x y]) -> SELECT p.c1 AS x, p.c2 AS y FROM parent AS p
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; ([ancestor x y] [parent x z] [ancestor z y]) -> SELECT p.c1 AS x, a.y AS y FROM parent AS p JOIN ancestor AS a WHERE p.c1 = a.x AND p.c2 = a.y
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; [ancestor x :john] -> WITH RECURSIVE ancestor(x, y) AS (SELECT ... UNION SELECT ...) SELECT a.c1 AS x FROM ancestor AS a WHERE a.y = 'john'
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; ([ancestor :bob x] [ancestor x :john]) -> SELECT 'bob' AS c1, a.c1 AS c2 FROM ancestor AS a WHERE a.c2 = 'john'
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; queries with arithmetic operations (function calls?)
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; [p x y] [q (+ x 1)] -> SELECT p.c1 AS x, p.c2 AS y FROM p JOIN q WHERE q.c1 = p.c1 + 1
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; [p (+ x 1) y] [q x] -> SELECT q.c1 AS x, p.c2 AS y FROM p JOIN q WHERE p.c1 = q.c1 + 1
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; [p (+ x 1) x] -> SELECT p.c2 AS x FROM p WHERE p.c1 = p.c2 + 1
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; queries with comparisons
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; [p x y] (< x 5) -> SELECT p.c1 AS x, p.c2 AS y FROM p WHERE p.c1 < 5
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; [p x y] (= x y) -> unnecessary but supported, can be written (p x x)
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; [p x y] (= x (+ y 1)) -> unnecessary but supported, can be written (p (+ x 1) x)?
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; confusing expressions we probably won't support:
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; [p (+ x 1) (* x 2)] -> SELECT p.c1 - 1 AS x FROM p WHERE p.c1 + 1 = p.c2 * 2??
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; no, that's not right - this says x+1 = c1 AND x*2 = c2
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; [p (+ x 1) (* x 2)] -> SELECT p.c1 - 1 AS x FROM p WHERE p.c2 = (p.c1 - 1) * 2
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; [p (+ x 1) y] -> meaningless? or...
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; -> SELECT p.c1 - 1 AS x, p.c2 AS y FROM p
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; is there a way to trick sql into generating x = p.c1 - 1 from p.c1 = x + 1?
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; [p z y] (= z (+ x 1))
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; unsupported: inline comparisons
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; [p (< x 5) y] -> SELECT p.c1 AS x, p.c2 AS y FROM p WHERE p.c1 < 5 -- does this make sense? seems hard to read, hard to parse
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; insert:
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; [p 1 2] -> INSERT INTO p (c1, c2) VALUES (1, 2)
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; [p 1 (+ 2 3)] -> INSERT INTO p (c1, c2) VALUES (1, 2 + 3)
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; (!+ [p (+ x 1) 3] [q x]) -> INSERT INTO p (c1, c2) SELECT q.c1 + 1 AS c1, 3 AS c2 FROM q
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; delete:
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; (!- [p _ _]) -> DELETE FROM p
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; (!- [p 1 _]) -> DELETE FROM p WHERE p.c1 = 1
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; augh sqlite doesn't support joins on delete! The most generic solution:
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; (!- [p 1 x] [q x]) -> DELETE FROM p WHERE p._rowid_ IN (SELECT p._rowid_ FROM p JOIN q WHERE p.c1 = 1 AND p.c2 = q.c1)
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; update:
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; (!= [q (+ x 1)] [q x]) -> UPDATE q SET c1 = q.c1 + 1
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; (!= [p (+ x 1) _] [p x 3]) -> UPDATE p SET c1 = p.c1 + 1 WHERE p.c2 = 3
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; invalid update:
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; (!= [p (+ x 1) _] [q x]) -> UPDATE p SET c1 = q.c1 + 1 FROM q -- this is valid sql, but it's madness - enforce the first query clause matches table
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(fn cat [list sep ?f]
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"Join all the elements in list with the string sep. If ?f is supplied, it is called to transform each value in the list into a new value first."
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(table.concat (icollect [i v (ipairs list)] ((or ?f #$1) v i)) sep))
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(fn any [list pred]
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"Returns true if the supplied predicate function returns true for any values in list."
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(var found false)
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(each [_ v (ipairs list) :until found] (set found (pred v)))
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found)
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(fn append-if-missing [list value]
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"Adds value to the end of list if it is not currently included."
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(when (not (any list #(= $1 value)))
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(table.insert list value)))
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(fn countiter [max]
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"An iterator that counts from 1 to max, inclusive."
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(fn [_ iprev]
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(let [i (if iprev (+ iprev 1) 1)]
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(when (<= i max) i))))
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(fn quoteid [name] (.. "\"" (name:gsub "\"" "\"\"") "\""))
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(fn Compiler.new [self]
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(set self.tables {})
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(set self.rules {}))
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(fn Compiler.deftable [self name ...]
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"Defines the column names of a table and their expected ordering"
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(when (. name self.rules) (error "tables and rules must not overlap"))
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(tset self.tables name [...])
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{:query (.. "CREATE TABLE " name "(" (cat [...] ", ") ")") :constants [] :selection []})
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(fn Compiler.defrule [self head ...]
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"Defines a new rule or expands the definition of an existing rule."
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(match head
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[:literal name] (let [rulelist (or (. self.rules name) [])]
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(table.insert rulelist [head ...])
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(tset self.rules name rulelist))
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_ (error "Expected literal for head, got " (fv head))))
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(fn new-analysis [?parent]
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"Creates a new empty analysis object. If ?parent is supplied, share the list of constants and referenced rules, as these are shared
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with the full SQL expression."
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{:variables [] ; list of all variable names referenced; used to determine which values to return from a query
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:variable-mapping {} ; a mapping from variable name to a SQL expr to which it is equal
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:selection [] ; list of all columns being selected, generally of the form [:as expr name]
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:clauses [] ; list of WHERE clauses, to be joined together by AND
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:tables [] ; list of tables or rules queried. (. tables 1) is generally aliased to _t1. All tables are inner joined.
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:constants (or (?. ?parent :constants) []) ; list of constant values to be bound to the prepared SQL expression
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:referenced-rules (or (?. ?parent :referenced-rules) [])}) ; list of all rules referenced by this expression, so they can be included
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(fn add-clause [analysis clause] (table.insert analysis.clauses clause))
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(fn Compiler.reference-name [self analysis name]
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"Called when a query references a new table. Appends the table or rule name to the end of analysis.tables
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and returns the index of the new value. Also updates analysis.referenced-rules as needed."
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(if (or (. self.rules name) (. self.tables name))
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(do (table.insert analysis.tables name)
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(when (. self.rules name)
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(append-if-missing analysis.referenced-rules name))
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(length analysis.tables))
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(error (.. "Unknown table / rule " name))))
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(fn Compiler.reference-variable [self analysis varname expr]
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"Called when a query expression (expr) is known to be equal to the value of varname - usually because
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the variable appears in the position of a particular rule or column. Defines a mapping from variable
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to expression if none exists, otherwise adds a new clause testing that the original mapping is equal
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to this new mapping, implementing unification."
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(when (not= varname :_)
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(match (. analysis.variable-mapping varname)
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mapping (add-clause analysis [:= mapping expr])
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nil (do (tset analysis.variable-mapping varname expr)
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(table.insert analysis.variables varname)))))
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; These are SQL functions that return boolean values and can be used as a standalone clause.
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(local comparitors (collect [_ op (ipairs [:< :> :<= :>= := :and :or])] op true))
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(fn Compiler.analyze-literal [self analysis literal]
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"Adds a literal of the form [table expr expr expr...] or a comparison expression of the form (op expr expr) to
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the analysis object. Typically this implies a join and some number of WHERE clauses."
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(match literal
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[:literal name params] (let [itable (self:reference-name analysis name)]
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(each [icolumn value (ipairs params)]
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(match value
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[:var varname] (self:reference-variable analysis varname [:column itable icolumn])
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[:const val] (add-clause analysis [:= [:column itable icolumn] [:const val]])
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(where [op] (= (. comparitors op) nil)) (add-clause analysis [:= [:column itable icolumn] value])
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_ (error (.. "expected var, const, or function, got " (fv value))))))
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(where [op] (. comparitors op)) (add-clause analysis literal)
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_ (error (.. "Expected literal or comparison but got " (fv literal)))))
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(local infix-ops (collect [_ op (ipairs [:+ :- :* :/ :< :> :<= :>= := :|| :and :or])] op true))
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(fn Compiler.gen-expr [self analysis expr]
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"Generates SQL code for a given expression tree."
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(match expr
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[:const val] (do (table.insert analysis.constants val) "?")
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[:column itable icolumn] (.. "_t" itable "."
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(match (. self.tables (. analysis.tables itable))
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colnames (quoteid (. colnames icolumn))
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_ (.. "c" icolumn)))
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[:rowid itable] (.. "_t" itable "._rowid_")
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[:as subexpr name] (.. (self:gen-expr analysis subexpr) " AS " (quoteid name))
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[:set column subexpr] (.. column " = " (self:gen-expr analysis subexpr))
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(where [:var name] (. analysis.variable-mapping name)) (self:gen-expr analysis (. analysis.variable-mapping name))
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(where [op lhs rhs] (. infix-ops op)) (.. "(" (self:gen-expr analysis lhs) " " op " " (self:gen-expr analysis rhs) ")")
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_ (error (.. "Unrecognized expression " (fv expr)))))
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(fn Compiler.gen-rule-clause [self analysis-parent [head & literals]]
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"Generates a SELECT statement for a given rule (potentially in a family of rules with the same name to be unioned together)"
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(let [analysis (new-analysis analysis-parent)]
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(each [_ literal (ipairs literals)] (self:analyze-literal analysis literal))
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(match head
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[:literal name params]
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(set analysis.selection (icollect [icolumn param (ipairs params)] [:as param (.. :c icolumn)]))
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_ (error (.. "Expected literal, got " (fv head))))
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(self:gen-select analysis)))
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(fn Compiler.gen-rule [self analysis name]
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"Generates a full expression for a rule family with the given name, to be placed in a WITH RECURSIVE block."
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(let [rule (. self.rules name)
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column-count (match rule
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[[[:literal _ clauses]]] (length clauses)
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_ (error (.. "Rule should be list of list of literals, was " (fv rule))))]
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(.. (quoteid name) "(" (table.concat (icollect [i (countiter column-count)] (.. "c" i)) ", ") ") AS NOT MATERIALIZED ("
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(cat rule " UNION " #(self:gen-rule-clause analysis $1)) ")")))
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(fn Compiler.gen-with-rules [self analysis]
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"Generates a WITH block containing all of the referenced rules found during analysis. Will append to the referenced-rules list
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as needed if rules depend on other rules, and only return when all requirements are satisfied."
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(let [rulequeries []]
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; ipairs will iterate over all referenced-rules even if gen-rule causes more to be appended
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(each [_ name (ipairs analysis.referenced-rules)]
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(table.insert rulequeries (self:gen-rule analysis name)))
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(if (> (length rulequeries) 0)
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(.. "WITH RECURSIVE " (cat rulequeries ", ") " ")
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"")))
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(fn Compiler.gen-select [self analysis]
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"Generates a SELECT statement for the query defined by analysis."
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(.. "SELECT "
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(if (> (length analysis.selection) 0)
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(cat analysis.selection ", " #(self:gen-expr analysis $1))
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"true")
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(if (> (length analysis.tables) 0)
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(.. " FROM " (cat analysis.tables " JOIN " #(.. (quoteid $1) " AS _t" $2)))
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"")
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(if (> (length analysis.clauses) 0)
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(.. " WHERE " (cat analysis.clauses " AND " #(self:gen-expr analysis $1)))
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"")))
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(fn tail [[ _ & result]] result)
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(fn Compiler.gen-update [self analysis]
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"Generates an UPDATE statement for the query defined by analysis."
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(.. "UPDATE " (quoteid (. analysis.tables 1)) " AS _t1 SET "
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(cat analysis.selection ", " #(self:gen-expr analysis $1))
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(if (>= (length analysis.tables) 2)
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(.. " FROM " (cat (tail analysis.tables) " JOIN " #(.. (quoteid $1) " AS _t" (+ $2 1))))
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"")
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(if (> (length analysis.clauses) 0)
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(.. " WHERE " (cat analysis.clauses " AND " #(self:gen-expr analysis $1)))
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"")))
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(fn Compiler.query [self ...]
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"Analyzes the given literals and generates an appropriate SELECT statement."
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(let [analysis (new-analysis)]
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(each [_ literal (ipairs [...])] (self:analyze-literal analysis literal))
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(set analysis.selection (icollect [_ varname (ipairs analysis.variables)] [:as (. analysis.variable-mapping varname) varname]))
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(set analysis.query (.. (self:gen-with-rules analysis) (self:gen-select analysis)))
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analysis))
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(fn Compiler.insert [self head ...]
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"Analyzes the given literals and generates an appropriate INSERT statement."
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(match head
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[:literal name params]
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(let [analysis (new-analysis)
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columns (. self.tables name)]
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(each [_ literal (ipairs [...])] (self:analyze-literal analysis literal))
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(set analysis.selection (icollect [icolumn param (ipairs params)]
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(match param
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[:var :_] nil
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expr [:as expr (. columns icolumn)])))
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(set analysis.query (.. (self:gen-with-rules analysis)
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"INSERT INTO " (quoteid name) " (" (cat analysis.selection ", " #(match $1 [:as _ column] (quoteid column))) ") "
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(self:gen-select analysis)))
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analysis)
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_ (error (.. "Expected literal, got " (fv head)))))
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(fn Compiler.delete [self head ...]
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"Analyzes the given literals and generates an appropriate DELETE statement."
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(match head
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[:literal name params]
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(let [analysis (new-analysis)]
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(each [_ literal (ipairs [head ...])] (self:analyze-literal analysis literal))
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(set analysis.selection [[:as [:rowid 1] :_rowid_]])
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(set analysis.query (.. (self:gen-with-rules analysis) "DELETE FROM " (quoteid name) " WHERE _rowid_ IN (" (self:gen-select analysis) ")"))
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analysis)
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_ (error (.. "Expected literal, got " (fv head)))))
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(fn Compiler.update [self newhead head ...]
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"Analyzes the given literals and generates an appropriate UPDATE statement."
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(match [newhead head]
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[[:literal name params] [:literal name]]
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(let [analysis (new-analysis)
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columns (. self.tables name)]
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(each [_ literal (ipairs [head ...])] (self:analyze-literal analysis literal))
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(set analysis.selection (icollect [icolumn param (ipairs params)]
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(match param
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[:var :_] nil
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expr [:set (. columns icolumn) expr])))
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(set analysis.query (.. (self:gen-with-rules analysis) (self:gen-update analysis)))
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analysis)))
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(setmetatable Compiler {:__call (fn [cls ...] (doto (setmetatable {} {:__index cls} ) (: :new ...)))})
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