On the Relation between Context-Free Grammars and Parsing Expression Grammars

Context-Free Grammars (CFGs) and Parsing Expression Grammars (PEGs) have several similarities and a few differences in both their syntax and semantics, but they are usually presented through formalisms that hinder a proper comparison. In this paper we present a new formalism for CFGs that highlights the similarities and differences between them. The new formalism borrows from PEGs the use of parsing expressions and the recognition-based semantics. We show how one way of removing non-determinism from this formalism yields a formalism with the semantics of PEGs. We also prove, based on these new formalisms, how LL(1) grammars define the same language whether interpreted as CFGs or as PEGs, and also show how strong-LL(k), right-linear, and LL-regular grammars have simple language-preserving translations from CFGs to PEGs

Cage and Joyce

James Joyce’s work was very important to the development of John Cage’s music and poetry. We can see it when we listen to his compositions or read his poems. Cage admired Joyce’s last novel, Finnegans Wake, praising mainly its language and circular structure. Cage decided to rewrite this novel, using a very personal method, that he called “chance operations”.Why did Cage decide to do it? I do not intend to explain his innermost motivations, but it is obvious that Cage created a very interesting poem, “Writing through Finnegans Wake”, that could be considered a very condensed version of Joyce’s masterpiece. After finishing his poem, Cage decided to transform it into a musical piece. He collected a great variety of sounds, using Joyce’s novel as a guide. So all the sounds that Cage collected are mentioned in Finnegans Wake – noises, voices, traditional songs, etc. All these sounds were played together, creating a sonorous chaos that suggests a dream, the dream of all mankind. Its title is taken from Finnegans Wake: “Roaratorio”. This musical composition is in its own right a masterpiece. Cage’s voice, reading his own poem, was added to this musical chaos.This composition was recorded and today is available on CD. I would like to play a small fragment of it. But before doing so, I would like to call attention to Cage’s poem, because it reveals Cage’s poetics very well.Cage loved Joyce’s words, but criticized his syntax, because it looked like the normal syntax of the English language. For this reason Cage decided to use words without normal syntax, creating a new kind of poetic language not found in Joyce’s novel.James Joyce’s work was very important to the development of John Cage’s music and poetry. We can see it when we listen to his compositions or read his poems. Cage admired Joyce’s last novel, Finnegans Wake, praising mainly its language and circular structure. Cage decided to rewrite this novel, using a very personal method, that he called “chance operations”.Why did Cage decide to do it? I do not intend to explain his innermost motivations, but it is obvious that Cage created a very interesting poem, “Writing through Finnegans Wake”, that could be considered a very condensed version of Joyce’s masterpiece. After finishing his poem, Cage decided to transform it into a musical piece. He collected a great variety of sounds, using Joyce’s novel as a guide. So all the sounds that Cage collected are mentioned in Finnegans Wake – noises, voices, traditional songs, etc. All these sounds were played together, creating a sonorous chaos that suggests a dream, the dream of all mankind. Its title is taken from Finnegans Wake: “Roaratorio”. This musical composition is in its own right a masterpiece. Cage’s voice, reading his own poem, was added to this musical chaos.This composition was recorded and today is available on CD. I would like to play a small fragment of it. But before doing so, I would like to call attention to Cage’s poem, because it reveals Cage’s poetics very well.Cage loved Joyce’s words, but criticized his syntax, because it looked like the normal syntax of the English language. For this reason Cage decided to use words without normal syntax, creating a new kind of poetic language not found in Joyce’s novel

Estado em crise: breve análise, vista sob a perspectiva

O Estado está em constante mutação. No futuro,tanto poderá ser mantido, ainda que reformulado, em face daflexibilização do conceito de soberania, como desaparecer,absorvido por entes de caráter supranacional. Aglobalização, insere-se nesse contexto. Com o Brasil nãopoderá ser diferente, devendo avançar a integração sócioeconômica no Mercosul, ou ceder espaço à formação da Alca.De qualquer sorte, pelo exaurimento do Neoliberalismo,impõe-se a formação de um novo Estado, de resgate dadimensão humana: o Estado Neosocial

Syntax Error Recovery in Parsing Expression Grammars

Parsing Expression Grammars (PEGs) are a formalism used to describe top-down parsers with backtracking. As PEGs do not provide a good error recovery mechanism, PEG-based parsers usually do not recover from syntax errors in the input, or recover from syntax errors using ad-hoc, implementation-specific features. The lack of proper error recovery makes PEG parsers unsuitable for using with Integrated Development Environments (IDEs), which need to build syntactic trees even for incomplete, syntactically invalid programs. We propose a conservative extension, based on PEGs with labeled failures, that adds a syntax error recovery mechanism for PEGs. This extension associates recovery expressions to labels, where a label now not only reports a syntax error but also uses this recovery expression to reach a synchronization point in the input and resume parsing. We give an operational semantics of PEGs with this recovery mechanism, and use an implementation based on such semantics to build a robust parser for the Lua language. We evaluate the effectiveness of this parser, alone and in comparison with a Lua parser with automatic error recovery generated by ANTLR, a popular parser generator.Comment: Published on ACM Symposium On Applied Computing 201

Li Po e Mao Tse-Tung em português

O poeta e tradutor Haroldo de Campos (1929-2003) “ reimaginou", em  língua portuguesa, a poesia clássica da China. Publicada originalmente em 1996, a antologia Escrito sobre jade, acrescida de novas traduções de sua autoria, saiu em segunda edição apenas em 2009

Caso exemplar de possessão: a pós-modernização de Mallarmé

Pretendo comentar brevemente o sublime irônico de Mallarmé,um poeta da segunda metade do século XIX, utilizando a versãopara o português, assinada por Augusto de Campos, do seu célebre poema “O Azul”

A pastoral de Lacoue-Labarthe

As narrativas de ficção que o filósofo francês Phillipe Lacoue-Labarthe publicou no século XX aliam a música (sinfonia e ópera) ao drama, a fim de introduzir o leitor na “pastoral inumana”, uma experiência literária bastante original