Syntax checking is far looser than with a programming language, How exactly do they want the page to be rendered? We're asking: What is the web page designer's intention, 2: Rendering a web page of HTML + ContentĪlthought I can't bring myself to call writing HTML writing a program. The real point of this step is to determine the programmer's intention, It must be syntactically correct before we run it.
#Finite state automata lexer code#
Perhaps called Perl o Write a compiler (combined lexer and parser) for that language's grammar o Write a program in that language o Lex and parse the source code In order to run a program we need to set up a range of pre-conditions: o Define the language, Let's consider some typical situations where lexing and parsing are the tools needed: 1: Running a program Note that the phases very conveniently run in alphabetical order: We lex and then we parse. The lex phase and the parse phase can be combined into a single process,īut I advocate always keeping them separate,Īnd I aim below to demonstrate why this is the best policy. There are many situations where the only path to a solution requires a lexer and a parser. This article explains why I (still) don't use any of these. It's good to know such tools are still available, Yacc) were so complex to operate I took the pledge to abstain. A History Lesson - In AbsentiaĪn article such as this would normally provide a summary of historical developments in this field,Įspecially as I first encountered parsing many years ago, The word parsing sometimes includes lexing and sometimes doesn't.Īnd our minds usually resolve the specific meaning intended by analysing the context in which the word is used. Start with Wikipedia's definitions: Lexing and Parsing. My Rules-of-Thumb for Writing Lexers/Parsersįor a more formal discussion than this article of what exactly lexing and parsing are, Something Fascinating about Rule Descriptors In Case You Think This is Going to be Complex Table of contents An Overview of Lexing and Parsing
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