Documentation Source Text

<table_of_contents>

<h1>Overview</h1>

<p>The SQL language parser for SQLite is generated using a code-generator
program called "Lemon".  The Lemon program reads a grammar of the input
language and emits C-code to implement a parser for that langauge.


<h2>Lemon Source Files And Documentation</h2>

<p>Lemon does not have its own source repository.  Rather, Lemon consists
of a few files in the SQLite source tree:

................................................................................
     variables and is therefore neither.  Reentrancy is especially
     important for SQLite since some SQL statements make recursive calls
     to the parser.  For example, when parsing a CREATE TABLE statement,
     SQLite invokes the parser recursively to generate an INSERT statement
     to make a new entry in the [sqlite_master] table.
<li><p>
     Lemon has the concept of a non-terminal destructor that can be
     used to reclaim memory or other resources following an syntax error
     or other aborted parse.
</ul>

<h2>Use of Lemon Within SQLite</h2>

<p>Lemon is used in two places in SQLite.

................................................................................

<ul>
<li><p>
Lemon has the concept of a "fallback" tokens.
The SQL language contains a large number of keywords and these keywords
have the potential to collide with identifier names.
Lemon has the ability to designate some keywords has being able to
"fallback" to an indentifier.  If the keyword appears in the input token
stream in a context that would otherwise be a syntax error, the token
is automatically transformed into its fallback before the syntax error
is raised.  This feature allows the parser to be very forgiving of
reserved words used as identifiers, which is a problem that comes up
frequently in the SQL language.

<li><p>
................................................................................
LL(1) parser generator tool named "Lime", but the source code for Lime
has been lost.

<p>The Lemon source code was originally written as separate source files,
and only later merged into a single "lemon.c" source file.

<p>The author of Lemon and SQLite (Hipp) reports that his C programming
skills were greatly enhanced by studing John Ousterhout's original
source code to Tcl.  Hipp discovered and studied Tcl in 1993.  Lemon
was written before then, and SQLite afterwards.  There is a clear
difference in the coding styles of these two products, with SQLite seeming
to be cleaner, more readable, and easier to maintain.

<table_of_contents>

<h1>Overview</h1>

<p>The SQL language parser for SQLite is generated using a code-generator
program called "Lemon".  The Lemon program reads a grammar of the input
language and emits C-code to implement a parser for that language.


<h2>Lemon Source Files And Documentation</h2>

<p>Lemon does not have its own source repository.  Rather, Lemon consists
of a few files in the SQLite source tree:

................................................................................
     variables and is therefore neither.  Reentrancy is especially
     important for SQLite since some SQL statements make recursive calls
     to the parser.  For example, when parsing a CREATE TABLE statement,
     SQLite invokes the parser recursively to generate an INSERT statement
     to make a new entry in the [sqlite_master] table.
<li><p>
     Lemon has the concept of a non-terminal destructor that can be
     used to reclaim memory or other resources following a syntax error
     or other aborted parse.
</ul>

<h2>Use of Lemon Within SQLite</h2>

<p>Lemon is used in two places in SQLite.

................................................................................

<ul>
<li><p>
Lemon has the concept of a "fallback" tokens.
The SQL language contains a large number of keywords and these keywords
have the potential to collide with identifier names.
Lemon has the ability to designate some keywords has being able to
"fallback" to an identifier.  If the keyword appears in the input token
stream in a context that would otherwise be a syntax error, the token
is automatically transformed into its fallback before the syntax error
is raised.  This feature allows the parser to be very forgiving of
reserved words used as identifiers, which is a problem that comes up
frequently in the SQL language.

<li><p>
................................................................................
LL(1) parser generator tool named "Lime", but the source code for Lime
has been lost.

<p>The Lemon source code was originally written as separate source files,
and only later merged into a single "lemon.c" source file.

<p>The author of Lemon and SQLite (Hipp) reports that his C programming
skills were greatly enhanced by studying John Ousterhout's original
source code to Tcl.  Hipp discovered and studied Tcl in 1993.  Lemon
was written before then, and SQLite afterwards.  There is a clear
difference in the coding styles of these two products, with SQLite seeming
to be cleaner, more readable, and easier to maintain.