Changes between Version 18 and Version 19 of PIRCDevelopment

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Timestamp:
08/06/09 17:37:35 (5 years ago)
Author:
kjs
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  • PIRCDevelopment

    v18 v19  
    149149For this discussion, it is assumed you have a basic understanding of the Flex program. For instance, you need to know what "state" means in Flex context. If you don't know, please refer to [http://flex.sourceforge.net/manual/ the Flex documentation page]. 
    150150 
    151 In order to make the heredoc preprocessor reentrant, no global variables are used. Instead, lines [source:/trunk/compilers/pirc/src/hdocprep.l#L83 83 to 98] define a struct global_state. The comments in the code briefly describe what each field is for, but they will be discussed in more detail later if we walk through the actual processing of the heredocs. A new instance of this struct can be created by invoking [source:/trunk/compilers/pirc/src/hdocprep.l#L157 init_global_state]. For now, it is useful to know that this struct has a pointer to a Parrot interpreter object, the name of the file being processed, and a pointer to the output file. 
    152  
    153 The function [source:/trunk/compilers/pirc/src/hdocprep.l#L208 process_heredocs] is the main function of the heredoc preprocessor that the main compiler program (PIRC) invokes. This function opens the file to be processed, initializes the lexer, creates a new global_state struct instance, as described above, invokes the lexer to do the processing and cleans up afterwards. 
    154  
     151In order to make the heredoc preprocessor reentrant, no global variables are used. Instead, lines [source:/trunk/compilers/pirc/src/hdocprep.l#L83 83 to 98] define a {{{struct global_state}}}. The comments in the code briefly describe what each field is for, but they will be discussed in more detail later if we walk through the actual processing of the heredocs. A new instance of this struct can be created by invoking [source:/trunk/compilers/pirc/src/hdocprep.l#L157 init_global_state]. For now, it is useful to know that this struct has a pointer to a Parrot interpreter object, the name of the file being processed, and a pointer to the output file. 
     152 
     153The function [source:/trunk/compilers/pirc/src/hdocprep.l#L208 process_heredocs] is the main function of the heredoc preprocessor that the main compiler program (PIRC) invokes. This function opens the file to be processed, initializes the lexer, creates a new {{{global_state}}} struct instance, as described above, invokes the lexer to do the processing and cleans up afterwards. 
     154 
     155We will now walk through two different scenarios, in order to simplify the discussion. Scenario 1 discussed the case of single heredoc parsing, and Scenario 2 discusses multiple heredoc parsing. Multiple heredoc parsing starts out with Scenario 1, but is a bit more advanced. 
     156 
     157==== Scenario 1: single heredoc parsing ==== 
     158 
     159Consider the following input: 
     160 
     161{{{ 
     162 
     163.sub main 
     164  $S0 = <<'EOS' 
     165This 
     166is 
     167a 
     168heredoc 
     169string. 
     170 
     171EOS 
     172.end 
     173  
     174}}} 
     175 
     176The lexer starts out in the {{{INITIAL}}} state by default (as per Flex specification). When reading input such as {{{<<'EOS'}}}, the rule on [source:/trunk/compilers/pirc/src/hdocprep.l#L306 line 306] is activated. The actual string ("EOS") is stored in the field {{{state->delimiter}}}, and an escaped {{{newline}}} character is stored in the {{{heredoc}}} buffer. 
     177 
     178==== Scenario 2: multiple heredoc parsing ==== 
     179 
     180==== POD parsing ==== 
    155181 
    156182== Macro layer ==