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<head><title>step -- step by single lines in the debugger</title>
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<div><h1>step -- step by single lines in the debugger</h1>
<div class="single"><h2>Synopsis</h2>
<ul><li><div class="list"><dl class="element"><dt class="heading">Usage: </dt><dd class="value"><div><tt>step n</tt></div>
</dd></dl>
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</li>
<li><div class="single">Inputs:<ul><li><span><tt>n</tt>, <span>an <a href="___Z__Z.html">integer</a></span></span></li>
</ul>
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</li>
<li><div class="single">Consequences:<ul><li>This command is active within the debugger. The current expression is executed and execution is continued until <tt>n</tt> lines of source code whose load depth is as large as <a href="_error__Depth.html" title="set the error printing depth">errorDepth</a> have been encountered. If <tt>n</tt> is omitted, then 1 is used. If <tt>n</tt> is negative then instead, <tt>n</tt> microsteps in the inner interpreter are executed and traced.</li>
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</li>
</ul>
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<div class="single"><h2>Description</h2>
<div><p>One useful way to debug code suspected of being in error is to insert an explicit error message, such as <tt>error "debug me"</tt>, and start stepping from there, as in the following demonstration.</p>
<table class="examples"><tr><td><pre>i1 : load "Macaulay2Doc/demo2.m2"</pre>
</td></tr>
<tr><td><pre>i2 : code f
o2 = /builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:6:7-12:13: --source code:
f = t -> (
x := 1;
error "debug me";
y := t+1;
z := 1/t;
w := x+t;
)</pre>
</td></tr>
<tr><td><pre>i3 : f 0
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6:(3):[1]: error: debug me
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6:(3):[1]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:8:6-8:6: --source code:
error "debug me";</pre>
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<tr><td><pre>ii4 : help
--loading the Macaulay2 documentation from /builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/
oo4 = --debugging control:
return -- bypass current expression, return null, stop
return x -- bypass current expression, return x, stop
step -- step 1 line
step n -- step n lines
step (-n) -- trace n microsteps
end (or eof char) -- enter debugger one level up
continue -- leave the debugger, continuing execution
-- with current expression
break -- leave the debugger, returning to top level
--debugging information:
listLocalSymbols -- display local symbols and their values
listUserSymbols -- display user symbols and their values
current -- the current expression; initially, the one
-- that produced an error
code current -- source code of current expression
value current -- execute current expression, obtain value
disassemble current -- display microcode of current expression
currentString -- the string being evaluated by 'value', if
-- an error occurred within it
-- emacs commands in *M2* buffer:
RET -- on an file/position line, go to source</pre>
</td></tr>
<tr><td><pre>ii5 : return
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --stepping limit reached
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8-9:13: --source code:
y := t+1;</pre>
</td></tr>
<tr><td><pre>ii6 : disassemble current
oo6 = (store 2 0 (2-OP + (fetch 0 0) 1))</pre>
</td></tr>
<tr><td><pre>ii7 : step(-3)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:8:(3):[1]: --evaluating: (store 2 0 (2-OP + (fetch 0 0) 1))
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:12:(3):[1]: --evaluating: (2-OP + (fetch 0 0) 1)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:11:(3):[1]: --evaluating: (fetch 0 0)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13:(3):[1]: --stepping limit reached
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13:(3):[1]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:9:13-9:13: --source code:
y := t+1;</pre>
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<tr><td><pre>ii8 : step
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8:(3):[1]: --stepping limit reached
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8:(3):[1]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:8-10:13: --source code:
z := 1/t;</pre>
</td></tr>
<tr><td><pre>ii9 : step
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:12:(3):[1]: error: division by zero
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:12:(3):[1]: --entering debugger (type help to see debugger commands)
/builddir/build/BUILD/Macaulay2-1.3.1-r10737/Macaulay2/packages/Macaulay2Doc/demo2.m2:10:11-10:13: --source code:
z := 1/t;</pre>
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<tr><td><pre>ii10 : t
oo10 = 0</pre>
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<div class="single"><h2>See also</h2>
<ul><li><span><a href="_debugging.html" title="">debugging</a></span></li>
</ul>
</div>
<div class="waystouse"><h2>For the programmer</h2>
<p>The object <a href="_step.html" title="step by single lines in the debugger">step</a> is <span>a <a href="___Keyword.html">keyword</a></span>.</p>
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