4.2.3 PTHL Code to Write

We don’t need several directories, you can program in the top level of the package.

You must write:

src/scantiger.ll

The scanner.

lval supports strings, integers and even symbols. Nevertheless, symbols (i.e., identifiers) are returned as plain C++ strings for the time being: the class misc::symbol is introduced in TC-1.

If the environment variable SCAN is defined (to whatever value) Flex scanner debugging traces are enabled, i.e., set the variable yy_flex_debug to 1.

src/parsetiger.yy

The parser, and maybe main if you wish. Bison advanced features will be used in TC-1.

• − Use C++ (e.g., C++ I/O streams, strings, etc.)
• − Use C++ features of Bison.
• − Use locations.
• − Use ‘%expect 0’ to have Bison report conflicts are genuine errors.
• − Use the ‘%require "3.0"’ directive to prevent any problem due to old versions of Bison.
• − Use the ‘%define api.value.type variant’ directive to ask Bison for C++ object support in the semantic values. Without this, Bison uses union, which can be used to store objects (just Plain Old Data), hence pointers and dynamic allocation must be used.
• − Use the ‘%define api.token.constructor’ directive to request that symbols be handled as a whole (token type, location, and possibly semantic value) in the scanner through ‘parse::parser::make_SYMBOL’ routines.
• − Use the environment variable PARSE to enable parser traces, i.e., to set yydebug to 1, run:

  PARSE=1 tc foo.tig
  

• − Use %printer to improve the tracing of semantic values. For instance,

  %define api.value.type variant
  %token <int> INT "integer"
  %printer { yyo << $$; } <int>
  

Makefile

This file is mandatory. Running make must build an executable tc in the root directory. The GNU Build System is not mandatory: TC-1 introduces Autoconf, Automake etc. You may use it, in which case we will run configure before make.