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| <a name="Basic-Guile"></a> |
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| Next: <a href="Guile-Configuration.html#Guile-Configuration" accesskey="n" rel="next">Guile Configuration</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="Basic-Guile-1"></a> |
| <h4 class="subsubsection">23.3.3.1 Basic Guile</h4> |
| |
| <a name="index-guile-stdout"></a> |
| <a name="index-guile-pagination"></a> |
| <p>At startup, <small>GDB</small> overrides Guile’s <code>current-output-port</code> and |
| <code>current-error-port</code> to print using <small>GDB</small>’s output-paging streams. |
| A Guile program which outputs to one of these streams may have its |
| output interrupted by the user (see <a href="Screen-Size.html#Screen-Size">Screen Size</a>). In this |
| situation, a Guile <code>signal</code> exception is thrown with value <code>SIGINT</code>. |
| </p> |
| <p>Guile’s history mechanism uses the same naming as <small>GDB</small>’s, |
| namely the user of dollar-variables (e.g., $1, $2, etc.). |
| The results of evaluations in Guile and in GDB are counted separately, |
| <code>$1</code> in Guile is not the same value as <code>$1</code> in <small>GDB</small>. |
| </p> |
| <p><small>GDB</small> is not thread-safe. If your Guile program uses multiple |
| threads, you must be careful to only call <small>GDB</small>-specific |
| functions in the <small>GDB</small> thread. |
| </p> |
| <p>Some care must be taken when writing Guile code to run in |
| <small>GDB</small>. Two things are worth noting in particular: |
| </p> |
| <ul> |
| <li> <small>GDB</small> installs handlers for <code>SIGCHLD</code> and <code>SIGINT</code>. |
| Guile code must not override these, or even change the options using |
| <code>sigaction</code>. If your program changes the handling of these |
| signals, <small>GDB</small> will most likely stop working correctly. Note |
| that it is unfortunately common for GUI toolkits to install a |
| <code>SIGCHLD</code> handler. |
| |
| </li><li> <small>GDB</small> takes care to mark its internal file descriptors as |
| close-on-exec. However, this cannot be done in a thread-safe way on |
| all platforms. Your Guile programs should be aware of this and |
| should both create new file descriptors with the close-on-exec flag |
| set and arrange to close unneeded file descriptors before starting a |
| child process. |
| </li></ul> |
| |
| <a name="index-guile-gdb-module"></a> |
| <p><small>GDB</small> introduces a new Guile module, named <code>gdb</code>. All |
| methods and classes added by <small>GDB</small> are placed in this module. |
| <small>GDB</small> does not automatically <code>import</code> the <code>gdb</code> module, |
| scripts must do this themselves. There are various options for how to |
| import a module, so <small>GDB</small> leaves the choice of how the <code>gdb</code> |
| module is imported to the user. |
| To simplify interactive use, it is recommended to add one of the following |
| to your ~/.gdbinit. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">guile (use-modules (gdb)) |
| </pre></div> |
| |
| <div class="smallexample"> |
| <pre class="smallexample">guile (use-modules ((gdb) #:renamer (symbol-prefix-proc 'gdb:))) |
| </pre></div> |
| |
| <p>Which one to choose depends on your preference. |
| The second one adds <code>gdb:</code> as a prefix to all module functions |
| and variables. |
| </p> |
| <p>The rest of this manual assumes the <code>gdb</code> module has been imported |
| without any prefix. See the Guile documentation for <code>use-modules</code> |
| for more information |
| (see <a href="http://www.gnu.org/software/guile/manual/html_node/Using-Guile-Modules.html#Using-Guile-Modules">Using Guile Modules</a> in <cite>GNU Guile Reference Manual</cite>). |
| </p> |
| <p>Example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) guile (value-type (make-value 1)) |
| ERROR: Unbound variable: value-type |
| Error while executing Scheme code. |
| (gdb) guile (use-modules (gdb)) |
| (gdb) guile (value-type (make-value 1)) |
| int |
| (gdb) |
| </pre></div> |
| |
| <p>The <code>(gdb)</code> module provides these basic Guile functions. |
| </p> |
| <dl> |
| <dt><a name="index-execute"></a>Scheme Procedure: <strong>execute</strong> <em>command <span class="roman">[</span>#:from-tty boolean<span class="roman">]</span> <span class="roman">[</span>#:to-string boolean<span class="roman">]</span></em></dt> |
| <dd><p>Evaluate <var>command</var>, a string, as a <small>GDB</small> CLI command. |
| If a <small>GDB</small> exception happens while <var>command</var> runs, it is |
| translated as described in |
| <a href="Guile-Exception-Handling.html#Guile-Exception-Handling">Guile Exception Handling</a>. |
| </p> |
| <p><var>from-tty</var> specifies whether <small>GDB</small> ought to consider this |
| command as having originated from the user invoking it interactively. |
| It must be a boolean value. If omitted, it defaults to <code>#f</code>. |
| </p> |
| <p>By default, any output produced by <var>command</var> is sent to |
| <small>GDB</small>’s standard output (and to the log output if logging is |
| turned on). If the <var>to-string</var> parameter is |
| <code>#t</code>, then output will be collected by <code>execute</code> and |
| returned as a string. The default is <code>#f</code>, in which case the |
| return value is unspecified. If <var>to-string</var> is <code>#t</code>, the |
| <small>GDB</small> virtual terminal will be temporarily set to unlimited width |
| and height, and its pagination will be disabled; see <a href="Screen-Size.html#Screen-Size">Screen Size</a>. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-history_002dref"></a>Scheme Procedure: <strong>history-ref</strong> <em>number</em></dt> |
| <dd><p>Return a value from <small>GDB</small>’s value history (see <a href="Value-History.html#Value-History">Value History</a>). The <var>number</var> argument indicates which history element to return. |
| If <var>number</var> is negative, then <small>GDB</small> will take its absolute value |
| and count backward from the last element (i.e., the most recent element) to |
| find the value to return. If <var>number</var> is zero, then <small>GDB</small> will |
| return the most recent element. If the element specified by <var>number</var> |
| doesn’t exist in the value history, a <code>gdb:error</code> exception will be |
| raised. |
| </p> |
| <p>If no exception is raised, the return value is always an instance of |
| <code><gdb:value></code> (see <a href="Values-From-Inferior-In-Guile.html#Values-From-Inferior-In-Guile">Values From Inferior In Guile</a>). |
| </p> |
| <p><em>Note:</em> <small>GDB</small>’s value history is independent of Guile’s. |
| <code>$1</code> in <small>GDB</small>’s value history contains the result of evaluating |
| an expression from <small>GDB</small>’s command line and <code>$1</code> from Guile’s |
| history contains the result of evaluating an expression from Guile’s |
| command line. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-history_002dappend_0021"></a>Scheme Procedure: <strong>history-append!</strong> <em>value</em></dt> |
| <dd><p>Append <var>value</var>, an instance of <code><gdb:value></code>, to <small>GDB</small>’s |
| value history. Return its index in the history. |
| </p> |
| <p>Putting into history values returned by Guile extensions will allow |
| the user convenient access to those values via CLI history |
| facilities. |
| </p></dd></dl> |
| |
| <dl> |
| <dt><a name="index-parse_002dand_002deval"></a>Scheme Procedure: <strong>parse-and-eval</strong> <em>expression</em></dt> |
| <dd><p>Parse <var>expression</var> as an expression in the current language, |
| evaluate it, and return the result as a <code><gdb:value></code>. |
| The <var>expression</var> must be a string. |
| </p> |
| <p>This function can be useful when implementing a new command |
| (see <a href="Commands-In-Guile.html#Commands-In-Guile">Commands In Guile</a>), as it provides a way to parse the |
| command’s arguments as an expression. |
| It is also is useful when computing values. |
| For example, it is the only way to get the value of a |
| convenience variable (see <a href="Convenience-Vars.html#Convenience-Vars">Convenience Vars</a>) as a <code><gdb:value></code>. |
| </p></dd></dl> |
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