Draft: Experimental sql package

x/README.md

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+## x
+
+Experimental packages.

x/postgres/README.md

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+# postgres
+
+Experimenting with predicates that use Go database/sql to query relational databases.
+
+Currently just supports Postgres but should be applicable to other DBs as well.

x/postgres/conn.go

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+package postgres
+
+import (
+	"database/sql"
+	"sync"
+	"sync/atomic"
+)
+
+var (
+	currentID   = new(int64)
+	connections sync.Map // connection id → *sql.DB
+)
+
+func nextID() int64 {
+	return atomic.AddInt64(currentID, 1)
+}
+
+func getConn(id int64) *sql.DB {
+	db, ok := connections.Load(id)
+	if !ok {
+		return nil
+	}
+	return db.(*sql.DB)
+}
+
+func setConn(id int64, db *sql.DB) {
+	connections.Store(id, db)
+}
+
+func deleteConn(id int64) {
+	connections.Delete(id)
+}

x/postgres/go.mod

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+module github.com/trealla-prolog/go/x/postgres
+
+go 1.20
+
+require (
+	github.com/lib/pq v1.10.9
+	github.com/trealla-prolog/go v0.13.9
+)
+
+require (
+	github.com/bytecodealliance/wasmtime-go/v8 v8.0.0 // indirect
+	golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53 // indirect
+)

x/postgres/go.sum

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+github.com/bytecodealliance/wasmtime-go/v8 v8.0.0 h1:jP4sqm2PHgm3+eQ50zCoCdIyQFkIL/Rtkw6TT8OYPFI=
+github.com/bytecodealliance/wasmtime-go/v8 v8.0.0/go.mod h1:tgazNLU7xSC2gfRAM8L4WyE+dgs5yp9FF5/tGebEQyM=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/lib/pq v1.10.9 h1:YXG7RB+JIjhP29X+OtkiDnYaXQwpS4JEWq7dtCCRUEw=
+github.com/lib/pq v1.10.9/go.mod h1:AlVN5x4E4T544tWzH6hKfbfQvm3HdbOxrmggDNAPY9o=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/stretchr/testify v1.8.1 h1:w7B6lhMri9wdJUVmEZPGGhZzrYTPvgJArz7wNPgYKsk=
+github.com/trealla-prolog/go v0.13.9 h1:ZZesdRT+RjEXWEaDI4extKFIAbmExUUOVvw5NvXxZAI=
+github.com/trealla-prolog/go v0.13.9/go.mod h1:PnMv/imG6iuoon0QUP/gSAqtHWeA55iV05W2dtOLn9U=
+golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53 h1:5llv2sWeaMSnA3w2kS57ouQQ4pudlXrR0dCgw51QK9o=
+golang.org/x/exp v0.0.0-20230425010034-47ecfdc1ba53/go.mod h1:V1LtkGg67GoY2N1AnLN78QLrzxkLyJw7RJb1gzOOz9w=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

x/postgres/library.go

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+package postgres
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/trealla-prolog/go/trealla"
+)
+
+var predicates = []struct {
+	name  string
+	arity int
+	proc  trealla.Predicate
+}{
+	{"postgres_open_url", 2, open_url_2},
+	{"postgres_execute", 4, execute_4},
+}
+
+func Register(ctx context.Context, pl trealla.Prolog) error {
+	for _, pred := range predicates {
+		if err := pl.Register(ctx, pred.name, pred.arity, pred.proc); err != nil {
+			return fmt.Errorf("failed to register predicate %s/%d: %w", pred.name, pred.arity, err)
+		}
+	}
+	return nil
+}

x/postgres/postgres.go

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+package postgres
+
+import (
+	"database/sql"
+
+	_ "github.com/lib/pq"
+
+	"github.com/trealla-prolog/go/trealla"
+	"github.com/trealla-prolog/go/trealla/terms"
+)
+
+func open_url_2(pl trealla.Prolog, _ trealla.Subquery, goal trealla.Term) trealla.Term {
+	pi := terms.PI(goal)
+	g, ok := goal.(trealla.Compound)
+	if !ok {
+		return terms.Throw(terms.TypeError("compound", goal, pi))
+	}
+
+	connStr, ok := g.Args[0].(string)
+	if !ok {
+		return terms.Throw(terms.TypeError("chars", g.Args[0], pi))
+	}
+
+	_, ok = g.Args[1].(trealla.Variable)
+	if !ok {
+		return terms.Throw(trealla.Atom("error").Of(trealla.Atom("uninstantiation_error").Of(g.Args[1]), pi))
+	}
+
+	db, err := sql.Open("postgres", connStr)
+	if err != nil {
+		return terms.Throw(dbError(err, pi))
+	}
+
+	id := nextID()
+	connections.Store(id, db)
+
+	g.Args[1] = trealla.Atom("pg").Of(id)
+	return g
+}
+
+func execute_4(pl trealla.Prolog, _ trealla.Subquery, goal trealla.Term) trealla.Term {
+	pi := terms.PI(goal)
+	g, ok := goal.(trealla.Compound)
+	if !ok {
+		return terms.Throw(terms.TypeError("compound", goal, pi))
+	}
+
+	handle, _ := g.Args[0].(trealla.Compound)
+	if handle.Functor != "pg" {
+		return terms.Throw(terms.TypeError("db_connection", g.Args[0], pi))
+	}
+
+	rawDB, ok := connections.Load(handle.Args[0].(int64))
+	if !ok {
+		return terms.Throw(terms.DomainError("db_connection", handle.Args[0], pi))
+	}
+	db := rawDB.(*sql.DB)
+
+	// TODO: apply query arguments
+
+	result, err := db.Exec(g.Args[1].(string))
+	_ = result
+	if err != nil {
+		return terms.Throw(dbError(err, pi))
+	}
+
+	// TODO: build result
+
+	return g
+}
+
+func dbError(err error, pi trealla.Term) trealla.Term {
+	return trealla.Atom("error").Of(trealla.Atom("db_error").Of(err.Error()), pi)
+}

x/postgres/postgres_test.go

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+package postgres
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/trealla-prolog/go/trealla"
+)
+
+func TestPG(t *testing.T) {
+	pl, err := trealla.New()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ctx := context.Background()
+	if err := Register(ctx, pl); err != nil {
+		t.Fatal(err)
+	}
+
+	t.Run("open connection", func(t *testing.T) {
+		ctx := context.Background()
+		ans, err := pl.QueryOnce(ctx, `postgres_open_url("user=postgres password=password dbname=postgres sslmode=disable", Handle)`)
+		if err != nil {
+			t.Fatal(err)
+		}
+		want := trealla.Atom("pg").Of(int64(1))
+		if !reflect.DeepEqual(ans.Solution["Handle"], want) {
+			t.Error("bad handle. want:", want, "got:", ans.Solution["Handle"])
+		}
+	})
+
+	t.Run("execute query", func(t *testing.T) {
+		ctx := context.Background()
+		ans, err := pl.QueryOnce(ctx, `postgres_open_url("user=postgres password=password dbname=postgres sslmode=disable", Handle), postgres_execute(Handle, "CREATE TABLE IF NOT EXISTS guestbook (id serial primary key, time timestamp default CURRENT_TIMESTAMP, author text, msg text);", [], Results).`)
+		if err != nil {
+			t.Fatal(err)
+		}
+		_ = ans
+		// TODO
+	})
+}