edtris/waltz/sqlog.fnl

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; sqlog, a datalog-like system built on sqlite
; may not actually have the full power of datalog OR the full power of sqlite
; datalog has a database of facts, and rules. facts are represented in sqlite directly as tables.
; rules are used by the sqlog engine when generating queries; typically they take the form
; of subqueries used in the WITH RECURSIVE clause.
; It would be possible to store them as views, but the view would need to be regenerated from
; its base rules anytime there is a change, so sqlog needs to know about them no matter what.
; Making sqlog manage them in-memory also allows us to use it to query arbitrary sqlite databases.
; Ideally we would persist rules as JSON in a special table; maybe sqlog_rules?
(local Object (require :core.object))
(local lume (require :lib.lume))
(local Sqlog (Object:extend))
; Generating SQL from Datalog should not be too complex, but it pays to start with the simplest
; case and build up from there.
; simple queries:
; (p x y) -> SELECT p.c1 AS x, p.c2 AS y FROM p
; (p 1 y) -> SELECT p.c2 AS y FROM p WHERE p.c1 = 1
; (q x) (p x 1) -> SELECT q.c1 AS x FROM q JOIN p WHERE p.c1 = q.c1 AND p.c2 = 1
; (p 1 2) -> SELECT true FROM p WHERE p.c1 = 1 AND p.c2 = 2
; (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
; queries using rules:
; [(ancestor x y) (parent x y)] -> SELECT p.c1 AS x, p.c2 AS y FROM parent AS p
; [(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
; (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'
(fn Sqlog.new [self]
(set self.tables {})
(set self.rules {}))
(fn Sqlog.deftable [self name ...]
"Defines the column names of a table and their expected ordering"
(when (. name self.rules) (error "tables and rules must not overlap"))
(tset self.tables name [...]))
(fn add-clause [analysis clause] (table.insert analysis.clauses clause))
(fn append-if-missing [list value]
(when (not (lume.any list #(= $1 value)))
(table.insert list value)))
(fn Sqlog.reference-name [self analysis name]
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(if (or (. self.rules name) (. self.tables name))
(do (table.insert analysis.tables name)
(length analysis.tables))
(error (.. "Unknown table / rule " name))))
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(fn Sqlog.reference-variable [self analysis varname expr]
(match (. analysis.variable-mapping varname)
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mapping (add-clause analysis [:= mapping expr])
nil (do (tset analysis.variable-mapping varname expr)
(table.insert analysis.variables varname))))
(fn Sqlog.analyze-literal [self analysis literal]
(match literal
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[:literal name params] (let [itable (self:reference-name analysis name)]
(each [icolumn value (ipairs params)]
(match value
[:var varname] (self:reference-variable analysis varname [:column itable icolumn])
[:const val] (add-clause analysis [:= [:column itable icolumn] [:const val]])
_ (error (.. "expected var or const, got " (fv value))))))
_ (error (.. "Expected literal but got " (fv literal)))))
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(fn new-analysis [] {:variables [] :variable-mapping {} :selection [] :clauses [] :tables [] :constants []})
(fn Sqlog.gen-expr [self analysis expr]
(match expr
[:const val] (do (table.insert analysis.constants val) "?")
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[:column itable icolumn] (.. "_t" itable "."
(match (. self.tables (. analysis.tables itable))
colnames (. colnames icolumn)
_ (.. "c" icolumn)))
[:as subexpr name] (.. (self:gen-expr analysis subexpr) " AS " name)
[:= lhs rhs] (.. (self:gen-expr analysis lhs) " = " (self:gen-expr analysis rhs))
_ (error (.. "Unrecognized expression " (fv expr)))))
(fn cat [list sep ?f]
(table.concat (icollect [i v (ipairs list)] ((or ?f #$1) v i)) sep))
(fn Sqlog.gen-select [self analysis]
(.. "SELECT "
(if (> (length analysis.selection) 0)
(cat analysis.selection ", " #(self:gen-expr analysis $1))
"true")
" FROM "
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(cat analysis.tables " JOIN " #(.. $1 " AS _t" $2))
(if (> (length analysis.clauses) 0)
(.. " WHERE " (cat analysis.clauses " AND " #(self:gen-expr analysis $1)))
"")))
(fn Sqlog.query [self ...]
(let [analysis (new-analysis)]
(each [_ literal (ipairs [...])] (self:analyze-literal analysis literal))
(set analysis.selection (icollect [_ varname (ipairs analysis.variables)] [:as (. analysis.variable-mapping varname) varname]))
[(self:gen-select analysis) analysis.constants]))
Sqlog