.TH "Parsing" 3o source: 2019-01-25 OCamldoc "OCaml library"
.SH NAME
Parsing \- The run-time library for parsers generated by ocamlyacc.
.SH Module
Module   Parsing
.SH Documentation
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Module
.BI "Parsing"
 : 
.B sig  end

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The run\-time library for parsers generated by 
.B ocamlyacc
\&.

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.I val symbol_start 
: 
.B unit -> int
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.B symbol_start
and 
.B Parsing\&.symbol_end
are to be called in the
action part of a grammar rule only\&. They return the offset of the
string that matches the left\-hand side of the rule: 
.B symbol_start()
returns the offset of the first character; 
.B symbol_end()
returns the
offset after the last character\&. The first character in a file is at
offset 0\&.

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.I val symbol_end 
: 
.B unit -> int
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See 
.B Parsing\&.symbol_start
\&.

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.I val rhs_start 
: 
.B int -> int
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Same as 
.B Parsing\&.symbol_start
and 
.B Parsing\&.symbol_end
, but
return the offset of the string matching the 
.B n
th item on the
right\-hand side of the rule, where 
.B n
is the integer parameter
to 
.B rhs_start
and 
.B rhs_end
\&. 
.B n
is 1 for the leftmost item\&.

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.I val rhs_end 
: 
.B int -> int
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See 
.B Parsing\&.rhs_start
\&.

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.I val symbol_start_pos 
: 
.B unit -> Lexing.position
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Same as 
.B symbol_start
, but return a 
.B position
instead of an offset\&.

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.I val symbol_end_pos 
: 
.B unit -> Lexing.position
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Same as 
.B symbol_end
, but return a 
.B position
instead of an offset\&.

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.I val rhs_start_pos 
: 
.B int -> Lexing.position
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Same as 
.B rhs_start
, but return a 
.B position
instead of an offset\&.

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.I val rhs_end_pos 
: 
.B int -> Lexing.position
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Same as 
.B rhs_end
, but return a 
.B position
instead of an offset\&.

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.I val clear_parser 
: 
.B unit -> unit
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Empty the parser stack\&. Call it just after a parsing function
has returned, to remove all pointers from the parser stack
to structures that were built by semantic actions during parsing\&.
This is optional, but lowers the memory requirements of the
programs\&.

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.I exception Parse_error 

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Raised when a parser encounters a syntax error\&.
Can also be raised from the action part of a grammar rule,
to initiate error recovery\&.

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.I val set_trace 
: 
.B bool -> bool
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Control debugging support for 
.B ocamlyacc
\-generated parsers\&.
After 
.B Parsing\&.set_trace true
, the pushdown automaton that
executes the parsers prints a trace of its actions (reading a token,
shifting a state, reducing by a rule) on standard output\&.
.B Parsing\&.set_trace false
turns this debugging trace off\&.
The boolean returned is the previous state of the trace flag\&.

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.B "Since"
3.11.0

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