177 lines
8.3 KiB
Fennel
177 lines
8.3 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 Object (require :core.object))
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(local lume (require :lib.lume))
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(local Sqlog (Object:extend))
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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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; 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, explicit equality checks (use unification instead)
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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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; [p x y] (= x y) -> unnecessary, can be written (p x x)
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; [p x y] (= x (+ y 1)) -> unnecessary, can be written (p (+ x 1) x)?
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(fn Sqlog.new [self]
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(set self.tables {})
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(set self.rules {}))
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(fn Sqlog.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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(fn Sqlog.defrule [self head ...]
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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 Sqlog.defrules [self ...]
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(for [i 1 (select :# ...)] (self:defrule (table.unpack (select i ...)))))
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(fn append-if-missing [list value]
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(when (not (lume.any list #(= $1 value)))
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(table.insert list value)))
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(fn add-clause [analysis clause] (table.insert analysis.clauses clause))
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(fn Sqlog.reference-name [self analysis name]
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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 Sqlog.reference-variable [self analysis varname expr]
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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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(fn Sqlog.analyze-literal [self analysis literal]
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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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[op & args] (add-clause analysis [:= [:column itable icolumn] value])
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_ (error (.. "expected var or const, got " (fv value))))))
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_ (error (.. "Expected literal but got " (fv literal)))))
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(fn new-analysis [?parent]
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{:variables []
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:variable-mapping {}
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:selection []
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:clauses []
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:tables []
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:constants (or (?. ?parent :constants) [])
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:referenced-rules (or (?. ?parent :referenced-rules) [])})
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(local infix-ops (collect [_ op (ipairs [:+ :- :* :/ :< :> :<= :>= := :|| :and :or])] op true))
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(fn Sqlog.gen-expr [self analysis expr]
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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 (. colnames icolumn)
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_ (.. "c" icolumn)))
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[:as subexpr name] (.. (self:gen-expr analysis subexpr) " AS " name)
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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 cat [list sep ?f]
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(table.concat (icollect [i v (ipairs list)] ((or ?f #$1) v i)) sep))
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(fn Sqlog.gen-rule-clause [self analysis-parent [head & literals]]
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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)]
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(match param
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[:var varname] [:as (. analysis.variable-mapping varname) (.. "c" icolumn)]
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[:const val] [:as param (.. "c" icolumn)]
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_ (error (.. "Expected const or var, got " (fv param))))))
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_ (error (.. "Expected literal, got " (fv head))))
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(self:gen-select analysis)))
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(fn Sqlog.gen-rule [self analysis name]
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(let [rule (. self.rules name)]
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(.. name "(" (cat rule ", " #(.. "c" $2)) ") AS NOT MATERIALIZED ("
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(cat rule " UNION " #(self:gen-rule-clause analysis $1)) ")")))
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(fn Sqlog.gen-with-rules [self analysis]
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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 Sqlog.gen-select [self 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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" FROM "
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(cat analysis.tables " JOIN " #(.. $1 " AS _t" $2))
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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 Sqlog.query [self ...]
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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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[(.. (self:gen-with-rules analysis) (self:gen-select analysis)) analysis.constants]))
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Sqlog
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