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POTranslate one term differently in one program
 

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    <p>I try to make a frontend for a kind of programs... there are 2 particularities:</p> <p>1) When we meet a string beginning with <code>=</code>, I want to read the rest of the string as a <code>formula</code> instead of a string value. For instance, <code>"123"</code>, <code>"TRUE"</code>, <code>"TRUE+123"</code> are considered having <code>string</code> as type, while <code>"=123"</code>, <code>"=TRUE"</code>, <code>"=TRUE+123"</code> are considered having <code>Syntax.formula</code> as type. By the way,</p> <pre><code>(* in syntax.ml *) and expression = | E_formula of formula | E_string of string ... and formula = | F_int of int | F_bool of bool | F_Plus of formula * formula | F_RC of rc and rc = | RC of int * int </code></pre> <p>2) Inside the formula, some strings are interpreted differently from outside. For instance, in a command <code>R4C5 := 4</code>, <code>R4C5</code> which is actually a variable, is considered as a <code>identifier</code>, while in <code>"=123+R4C5"</code> which tries to be translated to a formula, <code>R4C5</code> is translated as <code>RC (4,5): rc</code>.</p> <p>So I don't know how to realize this with 1 or 2 lexers, and 1 or 2 parsers. </p> <p>At the moment, I try to realize all in 1 lexer and 1 parser. Here is part of code, which doesn't work, it still considers <code>R4C5</code> as <code>identifier</code>, instead of <code>rc</code>:</p> <pre><code>(* in lexer.mll *) let begin_formula = double_quote "=" let end_formula = double_quote let STRING = double_quote ([^ "=" ])* double_quote rule token = parse ... | begin_formula { BEGIN_FORMULA } | 'R' { R } | 'C' { C } | end_formula { END_FORMULA } | lex_identifier as li { try Hashtbl.find keyword_table (lowercase li) with Not_found -&gt; IDENTIFIER li } | STRING as s { STRING s } ... (* in parser.mly *) expression: | BEGIN_FORMULA f = formula END_FORMULA { E_formula f } | s = STRING { E_string s } ... formula: | i = INTEGER { F_int i } | b = BOOL { F_bool b } | f0 = formula PLUS f1 = formula { F_Plus (f0, f1) } | rc { F_RC $1 } rc: | R i0 = INTEGER C i1 = INTEGER { RC (i0, i1) } </code></pre> <p>Could anyone help?</p> <p><strong>New idea:</strong> I am thinking of sticking on 1 lexer + 1 parser, and create a <em>entrypoint</em> for formula in lexer as what we do normally for <code>comment</code>... here are some updates in <code>lexer.mll</code> and <code>parser.mly</code>:</p> <pre><code>(* in lexer.mll *) rule token = parse ... | begin_formula { formula lexbuf } ... | INTEGER as i { INTEGER (int_of_string i) } | '+' { PLUS } ... and formula = parse | end_formula { token lexbuf } | INTEGER as i { INTEGER_F (int_of_string i) } | 'R' { R } | 'C' { C } | '+' { PLUS_F } | _ { raise (Lexing_error ("unknown in formula")) } (* in parser.mly *) expression: | formula { E_formula f } ... formula: | i = INTEGER_F { F_int i } | f0 = formula PLUS_F f1 = formula { F_Plus (f0, f1) } ... </code></pre> <p>I have done some tests, for instance to parse <code>"=R4"</code>, the problem is that it can parse well <code>R</code>, but it considers <code>4</code> as <code>INTEGER</code> instead of <code>INTEGER_F</code>, it seems that <code>formula lexbuf</code> needs to be added from time to time in the body of <code>formula</code> entrypoint (Though I don't understand why parsing in the body of <code>token</code> entrypoint works without always mentioning <code>token lexbuf</code>). I have tried several possibilities: <code>| 'R' { R; formula lexbuf }</code>, <code>| 'R' { formula lexbuf; R }</code>, etc. but it didn't work... ... Could anyone help?</p>
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