sqlog starts to generate some reasonable queries
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waltz/macros.fnl
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17
waltz/macros.fnl
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; (q X) -> q(X)
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; (q :x) -> q(x)
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; [(q X) (p X)] -> q(X) :- p(X)
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(fn clause [c]
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(match c
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(where [:unquote expr] (list? c)) `[:const ,expr]
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(where [name & params] (list? c)) `[:literal ,(tostring name) ,(icollect [_ param (ipairs params)] (clause param))]
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(where [head & tail] (sequence? c)) `[:clause ,(clause head) ,(icollect [_ elem (ipairs tail)] (clause elem))]
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(where v (sym? c)) `[:var ,(tostring v)]
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_ `[:const ,c]))
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(fn clauses [...]
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(icollect [_ c (ipairs [...]) :into `(values)] (clause c)))
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{: clause : clauses :$ clauses}
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101
waltz/sqlog.fnl
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101
waltz/sqlog.fnl
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; 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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(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 add-clause [analysis clause] (table.insert analysis.clauses clause))
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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 Sqlog.reference-name [self analysis name]
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(if (. self.rules name) (append-if-missing analysis.referenced-rules name)
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(. self.tables name) (append-if-missing analysis.tables name)
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(error (.. "Unknown table / rule " name))))
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(fn Sqlog.reference-variable [self analysis varname name icolumn]
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(match (. analysis.variable-mapping varname)
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mapping (add-clause analysis [:= mapping [:column name icolumn]])
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nil (do (tset analysis.variable-mapping varname [:column name icolumn])
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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] (do (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 name icolumn)
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[:const val] (add-clause analysis [:= [:column name icolumn] [:const val]])
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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 [] {:referenced-rules [] :variables [] :variable-mapping {} :selection [] :clauses [] :tables [] :constants []})
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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 name icolumn] (.. name "." (match (. self.tables name)
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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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[:= lhs rhs] (.. (self:gen-expr analysis lhs) " = " (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-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 (lume.concat analysis.tables analysis.referenced-rules) " JOIN ")
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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-select analysis) analysis.constants]))
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Sqlog
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