Add functions packages support (#419)

* Add packaged functions support

* Add tests for math.floor func

* Export FunctionsTable

* Extract func stuff into its own package

* Rename stuff

* Fix tests

* Move doc package to cmd/genji

* Adjust naming, typos

internal/sql/parser/expr.go

@@ -6,6 +6,7 @@ import (
 	"github.com/genjidb/genji/document"
 	"github.com/genjidb/genji/internal/environment"
 	"github.com/genjidb/genji/internal/expr"
+	"github.com/genjidb/genji/internal/expr/functions"
 	"github.com/genjidb/genji/internal/sql/scanner"
 	"github.com/genjidb/genji/internal/stringutil"
 )
@@ -190,11 +191,30 @@ func (p *Parser) parseUnaryExpr(allowed ...scanner.Token) (expr.Expr, error) {
 		p.Unscan()
 		return p.parseCastExpression()
 	case scanner.IDENT:
-		// if the next token is a left parenthesis, this is a function
-		if tok1, _, _ := p.Scan(); tok1 == scanner.LPAREN {
+		tok1, _, _ := p.Scan()
+		// if the next token is a left parenthesis, this is a global function
+		if tok1 == scanner.LPAREN {
 			p.Unscan()
 			p.Unscan()
 			return p.parseFunction()
+		} else {
+			// it may be a package function instead.
+			if tok1 == scanner.DOT {
+				if tok2, _, _ := p.Scan(); tok2 == scanner.IDENT {
+					if tok3, _, _ := p.Scan(); tok3 == scanner.LPAREN {
+						p.Unscan()
+						p.Unscan()
+						p.Unscan()
+						p.Unscan()
+						return p.parseFunction()
+					} else {
+						p.Unscan()
+						p.Unscan()
+					}
+				} else {
+					p.Unscan()
+				}
+			}
 		}
 		p.Unscan()
 		p.Unscan()
@@ -577,11 +597,23 @@ func (p *Parser) parseExprList(leftToken, rightToken scanner.Token) (expr.Litera
 // an optional coma-separated list of expressions and a closing parenthesis.
 func (p *Parser) parseFunction() (expr.Expr, error) {
 	// Parse function name.
-	fname, err := p.parseIdent()
+	funcName, err := p.parseIdent()
 	if err != nil {
 		return nil, err
 	}
 
+	// Parse optional package name
+	var pkgName string
+	if tok, _, _ := p.Scan(); tok == scanner.DOT {
+		pkgName = funcName
+		funcName, err = p.parseIdent()
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		p.Unscan()
+	}
+
 	// Parse required ( token.
 	if err := p.parseTokens(scanner.LPAREN); err != nil {
 		return nil, err
@@ -593,13 +625,17 @@ func (p *Parser) parseFunction() (expr.Expr, error) {
 			return nil, newParseError(scanner.Tokstr(tok, lit), []string{")"}, pos)
 		}
 
-		return &expr.CountFunc{Wildcard: true}, nil
+		return &functions.Count{Wildcard: true}, nil
 	}
 	p.Unscan()
 
 	// Check if the function is called without arguments.
 	if tok, _, _ := p.ScanIgnoreWhitespace(); tok == scanner.RPAREN {
-		return p.functions.GetFunc(fname)
+		def, err := p.packagesTable.GetFunc(pkgName, funcName)
+		if err != nil {
+			return nil, err
+		}
+		return def.Function()
 	}
 	p.Unscan()
 
@@ -625,7 +661,11 @@ func (p *Parser) parseFunction() (expr.Expr, error) {
 		return nil, err
 	}
 
-	return p.functions.GetFunc(fname, exprs...)
+	def, err := p.packagesTable.GetFunc(pkgName, funcName)
+	if err != nil {
+		return nil, err
+	}
+	return def.Function(exprs...)
 }
 
 // parseCastExpression parses a string of the form CAST(expr AS type).
@@ -657,7 +697,7 @@ func (p *Parser) parseCastExpression() (expr.Expr, error) {
 		return nil, err
 	}
 
-	return expr.CastFunc{Expr: e, CastAs: tp}, nil
+	return functions.Cast{Expr: e, CastAs: tp}, nil
 }
 
 // tokenIsAllowed is a helper function that determines if a token is allowed.