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the theory says about lex tool (I read ocamllex) it will convert a collection of regular expressions into C (OCaml) code for a DFA (actually in a NFA and also NFA2DFA). The formal definition of a DFA M is a 5 tuple M = { Q, Sigma, transition_function, q0, F}. What I found in the generated file is the following:

  • a record called __ocaml_lex_tables with fields from Lexing module
  • a recursive function

There is a mapping between the objects/structures of a DFA and the structures generated by ocamllex? I cannot 'see' it.... also I was googling for some help and I did not find any useful example.
The answer from ocamllex tool is meaningful in a DFA context e.g. 7 states, 279 transitions, table size 1158 bytes.

Is it a state transition table ? How to 'read' it ? Thank you for any link/hint !

dag
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ocamllex is focused on speed, so it will not have explicit states visible in generated code. The theoretical representation is not always the fastest one, in practice it is usually transformed to account for constant factor speed improvements. The states are most probably represented with indexes in the generated arrays. You can think of it as mapping back assembly code to the real source code - in the general case it is not possible to do immediately because the compiler performs some optimizations and strives for the most compact and effective code, same goes for ocamllex. And the interesting question is why do you want to do that??

ygrek
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  • hello and thank you for the details. I am studying that's the reason. I have found a way to have a different output from ocamllex, by using [-ml] option the output code will not use the Lexing module built-in automata interpreter. regards, – dag Jul 05 '13 at 17:01