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2786055df4
- New parser written from scratch, allows easier and complete parsing of the full S3 Select SQL syntax. Parser definition is directly provided by the AST defined for the SQL grammar. - Bring support to parse and interpret SQL involving JSON path expressions; evaluation of JSON path expressions will be subsequently added. - Bring automatic type inference and conversion for untyped values (e.g. CSV data).
119 lines
2.8 KiB
Go
119 lines
2.8 KiB
Go
package participle
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import (
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"errors"
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"io"
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"strconv"
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"strings"
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"github.com/alecthomas/participle/lexer"
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)
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type mapperByToken struct {
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symbols []string
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mapper Mapper
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}
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// DropToken can be returned by a Mapper to remove a token from the stream.
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var DropToken = errors.New("drop token") // nolint: golint
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// Mapper function for mutating tokens before being applied to the AST.
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//
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// If the Mapper func returns an error of DropToken, the token will be removed from the stream.
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type Mapper func(token lexer.Token) (lexer.Token, error)
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// Map is an Option that configures the Parser to apply a mapping function to each Token from the lexer.
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//
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// This can be useful to eg. upper-case all tokens of a certain type, or dequote strings.
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//
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// "symbols" specifies the token symbols that the Mapper will be applied to. If empty, all tokens will be mapped.
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func Map(mapper Mapper, symbols ...string) Option {
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return func(p *Parser) error {
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p.mappers = append(p.mappers, mapperByToken{
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mapper: mapper,
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symbols: symbols,
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})
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return nil
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}
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}
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// Unquote applies strconv.Unquote() to tokens of the given types.
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//
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// Tokens of type "String" will be unquoted if no other types are provided.
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func Unquote(types ...string) Option {
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if len(types) == 0 {
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types = []string{"String"}
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}
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return Map(func(t lexer.Token) (lexer.Token, error) {
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value, err := unquote(t.Value)
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if err != nil {
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return t, lexer.Errorf(t.Pos, "invalid quoted string %q: %s", t.Value, err.Error())
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}
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t.Value = value
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return t, nil
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}, types...)
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}
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func unquote(s string) (string, error) {
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quote := s[0]
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s = s[1 : len(s)-1]
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out := ""
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for s != "" {
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value, _, tail, err := strconv.UnquoteChar(s, quote)
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if err != nil {
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return "", err
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}
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s = tail
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out += string(value)
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}
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return out, nil
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}
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// Upper is an Option that upper-cases all tokens of the given type. Useful for case normalisation.
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func Upper(types ...string) Option {
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return Map(func(token lexer.Token) (lexer.Token, error) {
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token.Value = strings.ToUpper(token.Value)
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return token, nil
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}, types...)
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}
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// Elide drops tokens of the specified types.
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func Elide(types ...string) Option {
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return Map(func(token lexer.Token) (lexer.Token, error) {
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return lexer.Token{}, DropToken
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}, types...)
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}
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// Apply a Mapping to all tokens coming out of a Lexer.
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type mappingLexerDef struct {
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lexer.Definition
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mapper Mapper
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}
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func (m *mappingLexerDef) Lex(r io.Reader) (lexer.Lexer, error) {
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lexer, err := m.Definition.Lex(r)
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if err != nil {
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return nil, err
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}
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return &mappingLexer{lexer, m.mapper}, nil
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}
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type mappingLexer struct {
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lexer.Lexer
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mapper Mapper
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}
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func (m *mappingLexer) Next() (lexer.Token, error) {
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for {
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t, err := m.Lexer.Next()
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if err != nil {
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return t, err
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}
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t, err = m.mapper(t)
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if err == DropToken {
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continue
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}
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return t, err
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}
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}
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