Add DROP TABLE (eatonphil#8)

ast.go

@@ -64,6 +64,10 @@ type CreateTableStatement struct {
 	cols *[]*columnDefinition
 }
 
+type DropTableStatement struct {
+	name token
+}
+
 type InsertStatement struct {
 	table  token
 	cols   *[]*identifier
@@ -75,12 +79,14 @@ type AstKind uint
 const (
 	SelectKind AstKind = iota
 	CreateTableKind
+	DropTableKind
 	InsertKind
 )
 
 type Statement struct {
 	SelectStatement      *SelectStatement
 	CreateTableStatement *CreateTableStatement
+	DropTableStatement   *DropTableStatement
 	InsertStatement      *InsertStatement
 	Kind                 AstKind
 }

cmd/main.go

@@ -116,6 +116,12 @@ repl:
 					fmt.Println("Error creating table", err)
 					continue repl
 				}
+			case gosql.DropTableKind:
+				err = mb.DropTable(ast.Statements[0].DropTableStatement)
+				if err != nil {
+					fmt.Println("Error dropping table", err)
+					continue repl
+				}
 			case gosql.InsertKind:
 				err = mb.Insert(stmt.InsertStatement)
 				if err != nil {

lexer.go

@@ -18,6 +18,7 @@ const (
 	asKeyword     keyword = "as"
 	tableKeyword  keyword = "table"
 	createKeyword keyword = "create"
+	dropKeyword   keyword = "drop"
 	insertKeyword keyword = "insert"
 	intoKeyword   keyword = "into"
 	valuesKeyword keyword = "values"
@@ -204,6 +205,7 @@ func lexKeyword(source string, ic cursor) (*token, cursor, bool) {
 		valuesKeyword,
 		tableKeyword,
 		createKeyword,
+		dropKeyword,
 		whereKeyword,
 		fromKeyword,
 		intoKeyword,

memory.go

@@ -356,6 +356,14 @@ func (mb *MemoryBackend) CreateTable(crt *CreateTableStatement) error {
 	return nil
 }
 
+func (mb *MemoryBackend) DropTable(dt *DropTableStatement) error {
+	if _, ok := mb.tables[dt.name.value]; ok {
+		delete(mb.tables, dt.name.value)
+		return nil
+	}
+	return ErrTableDoesNotExist
+}
+
 func NewMemoryBackend() *MemoryBackend {
 	return &MemoryBackend{
 		tables: map[string]*table{},

parser.go

@@ -464,6 +464,32 @@ func parseCreateTableStatement(tokens []*token, initialCursor uint, delimiter to
 	}, cursor, true
 }
 
+func parseDropTableStatement(tokens []*token, initialCursor uint, delimiter token) (*DropTableStatement, uint, bool) {
+	cursor := initialCursor
+	ok := false
+
+	_, cursor, ok = parseToken(tokens, cursor, tokenFromKeyword(dropKeyword))
+	if !ok {
+		return nil, initialCursor, false
+	}
+
+	_, cursor, ok = parseToken(tokens, cursor, tokenFromKeyword(tableKeyword))
+	if !ok {
+		return nil, initialCursor, false
+	}
+
+	name, newCursor, ok := parseTokenKind(tokens, cursor, identifierKind)
+	if !ok {
+		helpMessage(tokens, cursor, "Expected table name")
+		return nil, initialCursor, false
+	}
+	cursor = newCursor
+
+	return &DropTableStatement{
+		name: *name,
+	}, cursor, true
+}
+
 func parseStatement(tokens []*token, initialCursor uint, delimiter token) (*Statement, uint, bool) {
 	cursor := initialCursor
 
@@ -492,6 +518,14 @@ func parseStatement(tokens []*token, initialCursor uint, delimiter token) (*Stat
 		}, newCursor, true
 	}
 
+	dpTbl, newCursor, ok := parseDropTableStatement(tokens, cursor, semicolonToken)
+	if ok {
+		return &Statement{
+			Kind:               DropTableKind,
+			DropTableStatement: dpTbl,
+		}, newCursor, true
+	}
+
 	return nil, initialCursor, false
 }