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|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
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<head><title>Operators</title>
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>
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<h3 class="sectionHead"><span class="titlemark">6.6 </span> <a
id="x38-630006.6"></a>Operators</h3>
<!--l. 334--><p class="noindent" ><a name="nip_label_sec:operators"></a>
<!--l. 336--><p class="indent" > <span
class="phvr7t-x-x-80">nip2</span>’s expression syntax is almost exactly the same as C,
with a few small changes. Table <a
href="#x38-630012">6.2<!--tex4ht:ref: tb:precedence --></a> lists all of <span
class="phvr7t-x-x-80">nip2</span>’s
operators in order of increasing precedence. If you’ve used
C, the differences are:
<ul class="itemize1">
<li class="itemize">C’s <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">?:</span></span></span> operator becomes <span
class="phvr7t-x-x-80">if-then-else</span>, see above
</li>
<li class="itemize">Like almost every functional language, <span
class="phvr7t-x-x-80">nip2 </span>uses
square brackets for list constants (see <span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>), so to
index a list, <span
class="phvr7t-x-x-80">nip2 </span>uses <span
class="phvr7t-x-x-80">?</span>
</li>
<li class="itemize"><span
class="phvr7t-x-x-80">nip2 </span>adds <span
class="phvr7t-x-x-80">@ </span>for function composition, see <span
class="cmsy-10"></span><a
href="#x38-690006.6.6">6.6.6<!--tex4ht:ref: sec:func --></a>
</li>
<li class="itemize">The <span
class="phvr7t-x-x-80">: </span>operator is infix list cons, see <span
class="cmsy-10"></span><a
href="nipguidese28.html#x39-710006.7">6.7<!--tex4ht:ref: sec:lists --></a>
</li>
<li class="itemize">The <span
class="phvr7t-x-x-80">++ </span>operator becomes an infix concatenation
operator, <span
class="phvr7t-x-x-80">– </span>becomes list difference. Again, see
<span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>
</li></ul>
<!--l. 363--><p class="indent" > The only slightly tricky point is that function application
binds very tightly (only list index and class project bind
more tightly). So the expression:
<div class="verbatim" id="verbatim-32">
jim = fred 2 + 3
</div>
<!--l. 369--><p class="nopar" >
<!--l. 371--><p class="noindent" >binds as:
<div class="verbatim" id="verbatim-33">
jim = (fred 2) + 3
</div>
<!--l. 376--><p class="nopar" >
<!--l. 378--><p class="noindent" >This is almost always the behaviour you want.
<!--l. 381--><p class="indent" > There are two special equality tests: <span
class="phvr7t-x-x-80">=== </span>and <span
class="phvr7t-x-x-80">!==</span>. These
test for pointer equality, that is, they return <span
class="phvr7t-x-x-80">true </span>if their
arguments refer to the same object. These are occasionally
useful for writing interactive functions.
<!--l. 387--><p class="indent" > <a
id="x38-630012"></a><hr class="float"><div class="float"
>
<div class="center"
>
<!--l. 387--><p class="noindent" >
<div class="tabular"> <table id="TBL-4" class="tabular"
cellspacing="0" cellpadding="0"
><colgroup id="TBL-4-1g"><col
id="TBL-4-1"></colgroup><colgroup id="TBL-4-2g"><col
id="TBL-4-2"></colgroup><colgroup id="TBL-4-3g"><col
id="TBL-4-3"></colgroup><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-1-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-1-1"
class="td11">Operator</td><td style="white-space:nowrap; text-align:left;" id="TBL-4-1-2"
class="td11">Associativity</td><td style="white-space:nowrap; text-align:left;" id="TBL-4-1-3"
class="td11">Description </td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-2-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-2-1"
class="td11"><span
class="phvr7t-x-x-80">if then else</span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-2-2"
class="td11">Right </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-2-3"
class="td11">If-then-else construct </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-3-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-3-1"
class="td11"><span
class="phvr7t-x-x-80">= </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-3-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-3-3"
class="td11">Form name/value pair </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-4-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-4-1"
class="td11"><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">||</span></span></span> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-4-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-4-3"
class="td11">Logical or </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-5-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-5-1"
class="td11"><span
class="phvr7t-x-x-80">&& </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-5-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-5-3"
class="td11">Logical and </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-6-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-6-1"
class="td11"><span
class="phvr7t-x-x-80">@ </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-6-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-6-3"
class="td11">Function composition (see <span
class="cmsy-10"></span><a
href="#x38-690006.6.6">6.6.6<!--tex4ht:ref: sec:func --></a>)</td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-7-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-7-1"
class="td11"><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">|</span></span></span> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-7-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-7-3"
class="td11">Bitwise or </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-8-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-8-1"
class="td11"><img
src="nipguide0x.png" alt="^ " class="circ" > </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-8-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-8-3"
class="td11">Bitwise exclusive or </td></tr><tr
style="vertical-align:baseline;" id="TBL-4-9-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-9-1"
class="td11"><span
class="phvr7t-x-x-80">& </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-9-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-9-3"
class="td11">Bitwise and</td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-10-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-10-1"
class="td11"><span
class="phvr7t-x-x-80">== </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-10-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-10-3"
class="td11">Equal to </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-11-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-11-1"
class="td11"><span
class="phvr7t-x-x-80">!= </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-11-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-11-3"
class="td11">Not equal to </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-12-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-12-1"
class="td11"><span
class="phvr7t-x-x-80">=== </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-12-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-12-3"
class="td11">Pointer equal to </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-13-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-13-1"
class="td11"><span
class="phvr7t-x-x-80">!== </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-13-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-13-3"
class="td11">Pointer not equal to </td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-14-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-14-1"
class="td11"><span
class="phvr7t-x-x-80"> </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-14-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-14-3"
class="td11">Less than </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-15-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-15-1"
class="td11"><span
class="phvr7t-x-x-80">= </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-15-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-15-3"
class="td11">Less than or equal to </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-16-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-16-1"
class="td11"><span
class="phvr7t-x-x-80"> </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-16-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-16-3"
class="td11">Greater than </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-17-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-17-1"
class="td11"><span
class="phvr7t-x-x-80">= </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-17-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-17-3"
class="td11">Greater than or equal to </td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-18-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-18-1"
class="td11"><span
class="phvr7t-x-x-80"> </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-18-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-18-3"
class="td11">Left shift </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-19-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-19-1"
class="td11"><span
class="phvr7t-x-x-80"> </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-19-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-19-3"
class="td11">Right shift </td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-20-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-20-1"
class="td11"><span
class="phvr7t-x-x-80">+ </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-20-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-20-3"
class="td11">Addition </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-21-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-21-1"
class="td11"><span
class="phvr7t-x-x-80">- </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-21-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-21-3"
class="td11">Subtraction </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-22-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-22-1"
class="td11"><span
class="phvr7t-x-x-80">* </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-22-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-22-3"
class="td11">Multiplication </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-23-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-23-1"
class="td11"><span
class="cmmi-10">∕ </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-23-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-23-3"
class="td11">Division </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-24-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-24-1"
class="td11"><span
class="phvr7t-x-x-80">% </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-24-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-24-3"
class="td11">Remainder after division </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-25-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-25-1"
class="td11"><span
class="phvr7t-x-x-80">! </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-25-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-25-3"
class="td11">Logical negation </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-26-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-26-1"
class="td11"><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">~</span></span></span> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-26-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-26-3"
class="td11">One’s complement </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-27-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-27-1"
class="td11"><span
class="phvr7t-x-x-80">++ </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-27-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-27-3"
class="td11">Join (see <span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>) </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-28-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-28-1"
class="td11"><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">--</span></span></span> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-28-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-28-3"
class="td11">Difference (see <span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>) </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-29-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-29-1"
class="td11"><span
class="phvr7t-x-x-80">- </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-29-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-29-3"
class="td11">Unary minus </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-30-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-30-1"
class="td11"><span
class="phvr7t-x-x-80">+ </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-30-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-30-3"
class="td11">Unary plus </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-31-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-31-1"
class="td11"><span
class="phvr7t-x-x-80">(</span><span
class="ptmri7t-">type</span><span
class="phvr7t-x-x-80">) </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-31-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-31-3"
class="td11">Type cast expression </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-32-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-32-1"
class="td11"><span
class="phvr7t-x-x-80">** </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-32-2"
class="td11">Right </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-32-3"
class="td11">Raise to power </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-33-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-33-1"
class="td11"><span
class="phvr7t-x-x-80">: </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-33-2"
class="td11"> </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-33-3"
class="td11">List CONS (see <span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>) </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-34-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-34-1"
class="td11"><span
class="ptmri7t-">space </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-34-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-34-3"
class="td11">Function application </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-35-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-35-1"
class="td11"><span
class="phvr7t-x-x-80">? </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-35-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-35-3"
class="td11">List index (see <span
class="cmsy-10"></span><a
href="#x38-680006.6.5">6.6.5<!--tex4ht:ref: sec:listsyntax --></a>) </td>
</tr><tr
style="vertical-align:baseline;" id="TBL-4-36-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-36-1"
class="td11"><span
class="phvr7t-x-x-80">. </span></td><td style="white-space:nowrap; text-align:left;" id="TBL-4-36-2"
class="td11">Left </td><td style="white-space:nowrap; text-align:left;" id="TBL-4-36-3"
class="td11">Class project (see <span
class="cmsy-10"></span><a
href="nipguidese32.html#x43-750006.11">6.11<!--tex4ht:ref: sec:class --></a>) </td>
</tr><tr
class="hline"><td><hr></td><td><hr></td><td><hr></td></tr><tr
style="vertical-align:baseline;" id="TBL-4-37-"><td style="white-space:nowrap; text-align:left;" id="TBL-4-37-1"
class="td11"> </td></tr></table></div></div>
<br /><div class="caption"
><span class="id">Table 6.2: </span><span
class="content"><span
class="phvr7t-x-x-80">nip2 </span>operators in order of increasing precedence</span></div><!--tex4ht:label?: x38-630012 -->
<!--l. 441--><p class="noindent" ><a name="nip_label_tb:precedence"></a>
</div><hr class="endfloat" />
<h4 class="subsectionHead"><span class="titlemark">6.6.1 </span> <a
id="x38-640006.6.1"></a>The real type</h4>
<!--l. 446--><p class="noindent" ><span
class="phvr7t-x-x-80">nip2 </span>has a single number type for integers and real numbers.
All are represented internally as 64-bit floating point values.
You can use the four standard arithmetic operators (<span
class="phvr7t-x-x-80">+</span>, <span
class="phvr7t-x-x-80">-</span>, <span
class="phvr7t-x-x-80">*</span>, <span
class="phvr7t-x-x-80">/</span>),
remainder after integer division (%), raise-to-power (<span
class="phvr7t-x-x-80">**</span>), the
relational operators (<span
class="phvr7t-x-x-80"></span>, <span
class="phvr7t-x-x-80">=</span>, <span
class="phvr7t-x-x-80"></span>, <span
class="phvr7t-x-x-80">=</span>, <span
class="phvr7t-x-x-80">==</span>), the bitwise logical
operators (<span
class="phvr7t-x-x-80">&</span>, <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">|</span></span></span>, <img
src="nipguide1x.png" alt="^ " class="circ" >, <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">~</span></span></span>), integer shift operators (<span
class="phvr7t-x-x-80"></span>, <span
class="phvr7t-x-x-80"></span>) and
unary negation and positive (<span
class="phvr7t-x-x-80">-</span>, <span
class="phvr7t-x-x-80">+</span>).
<!--l. 454--><p class="indent" > Other mathematical functions are pre-defined for you: <span
class="phvr7t-x-x-80">sin</span>,
<span
class="phvr7t-x-x-80">cos</span>, <span
class="phvr7t-x-x-80">tan</span>, <span
class="phvr7t-x-x-80">asin</span>, <span
class="phvr7t-x-x-80">acos</span>, <span
class="phvr7t-x-x-80">atan</span>, <span
class="phvr7t-x-x-80">log</span>, <span
class="phvr7t-x-x-80">log10</span>, <span
class="phvr7t-x-x-80">exp</span>, <span
class="phvr7t-x-x-80">exp10</span>, <span
class="phvr7t-x-x-80">ceil</span>, <span
class="phvr7t-x-x-80">floor</span>. Each
has the standard behaviour.
<!--l. 458--><p class="indent" > You can use type-casts on reals. However, they remain
64-bit floating point, the range is simply clipped. Casting to
<span
class="phvr7t-x-x-80">unsigned short </span>produces a 64-bit float whose fractional part
has been set to zero, and which has been clipped to the
range 0 to 65535. This may or may not cause rounding
problems.
<!--l. 463--><p class="indent" > You can write hexadecimal number constants as
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">0xff</span></span></span>.
<!--l. 465--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.2 </span> <a
id="x38-650006.6.2"></a>The complex type</h4>
<!--l. 467--><p class="noindent" >Complex numbers are rather sketchily implemented. They
are generally handy for representing vectors and coordinates
rather than for doing arithmetic, so the range of operations
is limited.
<!--l. 471--><p class="indent" > Complex constants are written as two numbers enclosed
in round brackets and separated by a comma. You can
use the four standard arithmetic operators (<span
class="phvr7t-x-x-80">+</span>, <span
class="phvr7t-x-x-80">-</span>, <span
class="phvr7t-x-x-80">*</span>, <span
class="phvr7t-x-x-80">/</span>),
raise-to-power (<span
class="phvr7t-x-x-80">**</span>), and unary negation and positive (<span
class="phvr7t-x-x-80">-</span>, <span
class="phvr7t-x-x-80">+</span>).
You can use <span
class="phvr7t-x-x-80">== </span>only of the relational operators. You can mix
complex and real numbers in expressions. You can cast reals
to complex and back. Use the functions <span
class="phvr7t-x-x-80">re </span>and <span
class="phvr7t-x-x-80">im </span>to extract
the real and imaginary parts.
<div class="verbatim" id="verbatim-34">
(12, 13) + 4 == (16, 13)
 <br />(12, 2 + 2) ==  (12, 4)
 <br />re (12, 13) == 12
 <br />im (12, 13) == 13
</div>
<!--l. 484--><p class="nopar" >
<!--l. 486--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.3 </span> <a
id="x38-660006.6.3"></a>The character type</h4>
<!--l. 488--><p class="noindent" >Character constants are written as single characters enclosed
in single quotes. You can use the relational operators (<span
class="phvr7t-x-x-80"></span>, <span
class="phvr7t-x-x-80">=</span>,
<span
class="phvr7t-x-x-80"></span>, <span
class="phvr7t-x-x-80">=</span>, <span
class="phvr7t-x-x-80">==</span>) to sort characters by ASCII order. You can
cast a character to a real to get its ASCII value. You
can cast a real ASCII value to a character. You can
use the standard C escapes to represent non-ASCII
characters.
<div class="verbatim" id="verbatim-35">
(int) 'A' == 65
 <br />(char) 65 == 'A'
 <br />is_digit x = '0' <= x && x <= '9'
 <br />newline == '\n'
</div>
<!--l. 500--><p class="nopar" >
<!--l. 502--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.4 </span> <a
id="x38-670006.6.4"></a>The boolean type</h4>
<!--l. 504--><p class="noindent" >The two boolean constants are written as <span
class="phvr7t-x-x-80">true </span>and <span
class="phvr7t-x-x-80">false</span>.
Boolean values are generated by the relational operators.
You can use the standard logical operators (<span
class="phvr7t-x-x-80">&&</span>, <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">||</span></span></span>, <span
class="phvr7t-x-x-80">!</span>). You
can use a boolean type as an argument in an <span
class="phvr7t-x-x-80">if-then-else</span>
expression.
<!--l. 509--><p class="indent" > As with C, the logical operators do not evaluate their
right-hand sides if their value can be determined just from
evaluating their left-hand sides.
<div class="verbatim" id="verbatim-36">
true && false == false
 <br />true || error "boink!" == true
 <br />if true then 12 else 13 == 12
</div>
<!--l. 516--><p class="nopar" >
<!--l. 518--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.5 </span> <a
id="x38-680006.6.5"></a>The list type</h4>
<!--l. 519--><p class="noindent" ><a name="nip_label_sec:listsyntax"></a>
<!--l. 521--><p class="indent" > Lists are created from two constructors. <span
class="phvr7t-x-x-80">[] </span>denotes the
empty list. The list construction operator (<span
class="phvr7t-x-x-80">:</span>, pronounced
CONS by LISP programmers) takes an item and a list, and
returns a new list with the item added to the front. As a
convenience, <span
class="phvr7t-x-x-80">nip2 </span>has a syntax for list constants. A list
constant is a list of items, separated by commas, and
enclosed in square brackets:
<div class="verbatim" id="verbatim-37">
12:[] == [12]
 <br />12:13:14:[] == 12:(13:(14:[])) ==
 <br />  [12,13,14]
 <br />[a+2,3,4] == (a+2):3:4:[]
 <br />[2]:[3,4] == [[2],3,4]
</div>
<!--l. 533--><p class="nopar" >
<!--l. 535--><p class="indent" > Use the functions <span
class="phvr7t-x-x-80">hd </span>and <span
class="phvr7t-x-x-80">tl </span>to take the head and the tail of
a list:
<div class="verbatim" id="verbatim-38">
hd [12,13,14] == 12
 <br />tl [12,13,14] == [13,14]
</div>
<!--l. 541--><p class="nopar" >
<!--l. 543--><p class="indent" > Use <span
class="phvr7t-x-x-80">.. </span>in a list constant to define a list generator. List
generators build lists of numbers for you:
<div class="verbatim" id="verbatim-39">
[1..10] == [1,2,3,4,5,6,7,8,9,10]
 <br />[1,3..10] == [1,3,5,7,9]
 <br />[10,9..1] == [10,9,8,7,6,5,4,3,2,1]
</div>
<!--l. 550--><p class="nopar" >
<!--l. 552--><p class="noindent" >List generators are useful for expressing iteration.
<!--l. 555--><p class="indent" > Lists may be infinite:
<div class="verbatim" id="verbatim-40">
[1..] == [1,2,3,4,5,6,7,8,9 ..]
 <br />[5,4..] == [5,4,3,2,1,0,-1,-2,-3 ..]
</div>
<!--l. 560--><p class="nopar" >
<!--l. 562--><p class="noindent" >Infinite lists are useful for expressing unbounded iteration.
See <span
class="cmsy-10"></span><a
href="nipguidese29.html#x40-720006.8">6.8<!--tex4ht:ref: sec:lazy --></a>.
<!--l. 566--><p class="indent" > You can write list comprehensions like this:
<div class="verbatim" id="verbatim-41">
[x :: x <- [1..]; x % 2 == 0]
</div>
<!--l. 570--><p class="nopar" >
<!--l. 572--><p class="noindent" >This could be read as <span
class="ptmri7t-">All x such that x is in </span><span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">[1..]</span></span></span> <span
class="ptmri7t-">and x is</span>
<span
class="ptmri7t-">even</span>, that is, the list of even numbers.
<!--l. 576--><p class="indent" > You can have any number of semicolon-separated
qualifiers and each one can be either a generator (like
<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">x</span><span
class="pcrr7t-"> <-</span><span
class="pcrr7t-"> [1..]</span></span></span>) introducing a new variable or pattern (see
<span
class="cmsy-10"></span><a
href="nipguidese30.html#x41-730006.9">6.9<!--tex4ht:ref: sec:pattern --></a>), or a predicate (like <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">x</span><span
class="pcrr7t-"> %</span><span
class="pcrr7t-"> 2</span><span
class="pcrr7t-"> ==</span><span
class="pcrr7t-"> 0</span></span></span>) which filters the
generators to the left of it.
<!--l. 581--><p class="indent" > Later generators change more rapidly, so for example:
<div class="verbatim" id="verbatim-42">
[(x, y) ::
 <br />  x <- [1..3]; y <- [x..3]] ==
 <br />    [(1, 1), (1, 2), (1, 3),
 <br />      (2, 2), (2, 3), (3, 3)]
</div>
<!--l. 588--><p class="nopar" >
<!--l. 590--><p class="indent" > You can nest list comprehensions to generate more
complex data structures. For example:
<div class="verbatim" id="verbatim-43">
[[x ⋆ y :: x <- [1..10]] ::
 <br />  y <- [1..10]]
</div>
<!--l. 596--><p class="nopar" >
<!--l. 598--><p class="noindent" >will generate a times-table.
<!--l. 601--><p class="indent" > You can use pattern-matching (see <span
class="cmsy-10"></span><a
href="nipguidese30.html#x41-730006.9">6.9<!--tex4ht:ref: sec:pattern --></a>) to loop over
several generators at the same time. For example:
<div class="verbatim" id="verbatim-44">
[(x, y) :: [x, y] <-
 <br />  zip2 [1..3] [1..3]] ==
 <br />    [(1, 1), (2, 2), (3, 3)]
</div>
<!--l. 608--><p class="nopar" >
<!--l. 610--><p class="indent" > As a convenience, lists of characters may be written
enclosed in double quotes:
<div class="verbatim" id="verbatim-45">
"abc" == ['a','b','c']
</div>
<!--l. 615--><p class="nopar" >
<!--l. 617--><p class="indent" > You can define a string constant which has the same form
as a variable name (that is, letters, numbers, underscore and
apostrophy only) with a <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">$</span></span></span> prefix. For example:
<div class="verbatim" id="verbatim-46">
$form7 == "form7"
</div>
<!--l. 623--><p class="nopar" >
<!--l. 625--><p class="noindent" ><span
class="phvr7t-x-x-80">nip2 </span>often uses these in option lists.
<!--l. 628--><p class="indent" > You can define a name, value pair with the <span
class="phvr7t-x-x-80">= </span>operator.
<div class="verbatim" id="verbatim-47">
$fred => 12 == ["fred", 12]
</div>
<!--l. 632--><p class="nopar" >
<!--l. 634--><p class="noindent" >Again, these pairs are frequently used to pass options to
objects.
<!--l. 637--><p class="indent" > A list may contain any object:
<div class="verbatim" id="verbatim-48">
[1,'a',true,[1,2,3]]
</div>
<!--l. 641--><p class="nopar" >
<!--l. 643--><p class="noindent" >Mixing types in a list tends to be confusing and should be
avoided. If you want to group a set of diverse objects, define
a class instead, see <span
class="cmsy-10"></span><a
href="nipguidese32.html#x43-750006.11">6.11<!--tex4ht:ref: sec:class --></a>.
<!--l. 648--><p class="indent" > Lists of lists of reals are useful for representing arrays.
<!--l. 650--><p class="indent" > You can use the list index operator (<span
class="phvr7t-x-x-80">?</span>) to extract an
element from a position in a list:
<div class="verbatim" id="verbatim-49">
[1,2,3] ? 0 == 1
 <br />"abc" ? 1 == 'b'
</div>
<!--l. 656--><p class="nopar" >
<!--l. 658--><p class="indent" > You can use the list join operator (<span
class="phvr7t-x-x-80">++</span>) to join two lists
together end-to-end.
<div class="verbatim" id="verbatim-50">
[1,2,3] ++ [4,5,6] == [1,2,3,4,5,6]
</div>
<!--l. 663--><p class="nopar" >
<!--l. 665--><p class="indent" > You can use the list difference operator (<span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">--</span></span></span>) to remove
elements of one list from another.
<div class="verbatim" id="verbatim-51">
[1..10] -- [4,5,6] == [1,2,3,7,8,9,10]
</div>
<!--l. 670--><p class="nopar" >
<!--l. 672--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.6 </span> <a
id="x38-690006.6.6"></a>The function type</h4>
<!--l. 673--><p class="noindent" ><a name="nip_label_sec:func"></a>
<!--l. 675--><p class="indent" > Functions are objects just like any other. You can pass
functions to other functions as parameters, store functions in
lists, and so on.
<!--l. 678--><p class="indent" > You can create anonymous functions with <span class="obeylines-h"><span class="verb"><span
class="pcrr7t-">\</span></span></span> (lambda).
For example:
<div class="verbatim" id="verbatim-52">
map (\x x + 2) [1..3] == [3, 4, 5]
</div>
<!--l. 682--><p class="nopar" >
<!--l. 684--><p class="indent" > You can nest lambdas to make multi-argument anonymous
functions, for example:
<div class="verbatim" id="verbatim-53">
map2 (\x\y x + y) [1..3] [2..5] ==
 <br />  [3, 5, 7]
</div>
<!--l. 689--><p class="nopar" >
<!--l. 691--><p class="indent" > You can compose functions with the <span
class="phvr7t-x-x-80">@ </span>operator.
For example, for two functions of one argument <span
class="phvr7t-x-x-80">f </span>and
<span
class="phvr7t-x-x-80">g</span>:
<div class="verbatim" id="verbatim-54">
f (g 2) == (f @ g) 2
</div>
<!--l. 696--><p class="nopar" >
<!--l. 698--><p class="noindent" >
<h4 class="subsectionHead"><span class="titlemark">6.6.7 </span> <a
id="x38-700006.6.7"></a>The image type</h4>
<!--l. 700--><p class="noindent" >These represent a low-level handle to a VIPS image
structure. You can make them with the <span
class="phvr7t-x-x-80">vips</span><span
class="phvr7t-x-x-80">_image </span>builtin,
and you can pass them as parameters to VIPS functions.
The <span
class="phvr7t-x-x-80">Image </span>class is built on top of them, see <span
class="cmsy-10"></span><a
href="nipguidese33.html#x44-840006.12.3">6.12.3<!--tex4ht:ref: sec:Image --></a>.
<!--l. 705--><p class="indent" > As an accident of history, <span
class="phvr7t-x-x-80">nip2 </span>also lets you do arithmetic
with them. This will probably be removed in the next
version or two, so it’s best to go through the higher-level
<span
class="phvr7t-x-x-80">Image </span>class.
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