doc/guide/localhost/SyntacticConventions

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  26 <h1>SyntacticConventions</h1>
  27 <div id="toc">
  28   <div id="toctitle">Table of Contents</div>
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  31 </div>
  32 <div id="content">
  33 <div id="preamble">
  34 <div class="sectionbody">
  35 <div class="paragraph"><p>Here are a number of syntactic conventions useful for programming in
  36 SML.</p></div>
  37 </div>
  38 </div>
  39 <div class="sect1">
  40 <h2 id="_general">General</h2>
  41 <div class="sectionbody">
  42 <div class="ulist"><ul>
  43 <li>
  44 <p>
  45 A line of code never exceeds 80 columns.
  46 </p>
  47 </li>
  48 <li>
  49 <p>
  50 Only split a syntactic entity across multiple lines if it doesn&#8217;t fit on one line within 80 columns.
  51 </p>
  52 </li>
  53 <li>
  54 <p>
  55 Use alphabetical order wherever possible.
  56 </p>
  57 </li>
  58 <li>
  59 <p>
  60 Avoid redundant parentheses.
  61 </p>
  62 </li>
  63 <li>
  64 <p>
  65 When using <span class="monospaced">:</span>, there is no space before the colon, and a single space after it.
  66 </p>
  67 </li>
  68 </ul></div>
  69 </div>
  70 </div>
  71 <div class="sect1">
  72 <h2 id="_identifiers">Identifiers</h2>
  73 <div class="sectionbody">
  74 <div class="ulist"><ul>
  75 <li>
  76 <p>
  77 Variables, record labels and type constructors begin with and use
  78 small letters, using capital letters to separate words.
  79 </p>
  80 <div class="listingblock">
  81 <div class="content"><div class="highlight"><pre><span class="n">cost</span><span class="w"></span>
  82 <span class="n">maxValue</span><span class="w"></span>
  83 </pre></div></div></div>
  84 </li>
  85 <li>
  86 <p>
  87 Variables that represent collections of objects (lists, arrays,
  88 vectors, &#8230;) are often suffixed with an <span class="monospaced">s</span>.
  89 </p>
  90 <div class="listingblock">
  91 <div class="content"><div class="highlight"><pre><span class="n">xs</span><span class="w"></span>
  92 <span class="n">employees</span><span class="w"></span>
  93 </pre></div></div></div>
  94 </li>
  95 <li>
  96 <p>
  97 Constructors, structure identifiers, and functor identifiers begin
  98 with a capital letter.
  99 </p>
 100 <div class="listingblock">
 101 <div class="content"><div class="highlight"><pre><span class="n">Queue</span><span class="w"></span>
 102 <span class="n">LinkedList</span><span class="w"></span>
 103 </pre></div></div></div>
 104 </li>
 105 <li>
 106 <p>
 107 Signature identifiers are in all capitals, using <span class="monospaced">_</span> to separate
 108 words.
 109 </p>
 110 <div class="listingblock">
 111 <div class="content"><div class="highlight"><pre><span class="n">LIST</span><span class="w"></span>
 112 <span class="n">BINARY_HEAP</span><span class="w"></span>
 113 </pre></div></div></div>
 114 </li>
 115 </ul></div>
 116 </div>
 117 </div>
 118 <div class="sect1">
 119 <h2 id="_types">Types</h2>
 120 <div class="sectionbody">
 121 <div class="ulist"><ul>
 122 <li>
 123 <p>
 124 Alphabetize record labels.  In a record type, there are spaces after
 125 colons and commas, but not before colons or commas, or at the
 126 delimiters <span class="monospaced">{</span> and <span class="monospaced">}</span>.
 127 </p>
 128 <div class="listingblock">
 129 <div class="content"><div class="highlight"><pre><span class="p">{</span><span class="n">bar</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="p">,</span><span class="w"> </span><span class="n">foo</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="p">}</span><span class="w"></span>
 130 </pre></div></div></div>
 131 </li>
 132 <li>
 133 <p>
 134 Only split a record type across multiple lines if it doesn&#8217;t fit on
 135 one line. If a record type must be split over multiple lines, put one
 136 field per line.
 137 </p>
 138 <div class="listingblock">
 139 <div class="content"><div class="highlight"><pre><span class="p">{</span><span class="n">bar</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="p">,</span><span class="w"></span>
 140 <span class="w"> </span><span class="n">foo</span><span class="p">:</span><span class="w"> </span><span class="n">real</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="p">,</span><span class="w"></span>
 141 <span class="w"> </span><span class="n">zoo</span><span class="p">:</span><span class="w"> </span><span class="n">bool</span><span class="p">}</span><span class="w"></span>
 142 </pre></div></div></div>
 143 </li>
 144 <li>
 145 <p>
 146 In a tuple type, there are spaces before and after each <span class="monospaced">*</span>.
 147 </p>
 148 <div class="listingblock">
 149 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 150 </pre></div></div></div>
 151 </li>
 152 <li>
 153 <p>
 154 Only split a tuple type across multiple lines if it doesn&#8217;t fit on
 155 one line.  In a tuple type split over multiple lines, there is one
 156 type per line, and the <span class="monospaced">*</span>-s go at the beginning of the lines.
 157 </p>
 158 <div class="listingblock">
 159 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"></span>
 160 <span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>
 161 <span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 162 </pre></div></div></div>
 163 <div class="paragraph"><p>It may also be useful to parenthesize to make the grouping more
 164 apparent.</p></div>
 165 <div class="listingblock">
 166 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">int</span><span class="w"></span>
 167 <span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>
 168 <span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="p">)</span><span class="w"></span>
 169 </pre></div></div></div>
 170 </li>
 171 <li>
 172 <p>
 173 In an arrow type split over multiple lines, put the arrow at the
 174 beginning of its line.
 175 </p>
 176 <div class="listingblock">
 177 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 178 <span class="p">-&gt;</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>
 179 </pre></div></div></div>
 180 <div class="paragraph"><p>It may also be useful to parenthesize to make the grouping more
 181 apparent.</p></div>
 182 <div class="listingblock">
 183 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 184 <span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">bool</span><span class="p">)</span><span class="w"></span>
 185 </pre></div></div></div>
 186 </li>
 187 <li>
 188 <p>
 189 Avoid redundant parentheses.
 190 </p>
 191 </li>
 192 <li>
 193 <p>
 194 Arrow types associate to the right, so write
 195 </p>
 196 <div class="listingblock">
 197 <div class="content"><div class="highlight"><pre><span class="n">a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">b</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">c</span><span class="w"></span>
 198 </pre></div></div></div>
 199 <div class="paragraph"><p>not</p></div>
 200 <div class="listingblock">
 201 <div class="content"><div class="highlight"><pre><span class="n">a</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="p">(</span><span class="n">b</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">c</span><span class="p">)</span><span class="w"></span>
 202 </pre></div></div></div>
 203 </li>
 204 <li>
 205 <p>
 206 Type constructor application associates to the left, so write
 207 </p>
 208 <div class="listingblock">
 209 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"> </span><span class="n">ref</span><span class="w"> </span><span class="n">list</span><span class="w"></span>
 210 </pre></div></div></div>
 211 <div class="paragraph"><p>not</p></div>
 212 <div class="listingblock">
 213 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="n">ref</span><span class="p">)</span><span class="w"> </span><span class="n">list</span><span class="w"></span>
 214 </pre></div></div></div>
 215 </li>
 216 <li>
 217 <p>
 218 Type constructor application binds more tightly than a tuple type,
 219 so write
 220 </p>
 221 <div class="listingblock">
 222 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"> </span><span class="n">list</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="w"> </span><span class="n">list</span><span class="w"></span>
 223 </pre></div></div></div>
 224 <div class="paragraph"><p>not</p></div>
 225 <div class="listingblock">
 226 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="n">list</span><span class="p">)</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="p">(</span><span class="n">bool</span><span class="w"> </span><span class="n">list</span><span class="p">)</span><span class="w"></span>
 227 </pre></div></div></div>
 228 </li>
 229 <li>
 230 <p>
 231 Tuple types bind more tightly than arrow types, so write
 232 </p>
 233 <div class="listingblock">
 234 <div class="content"><div class="highlight"><pre><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 235 </pre></div></div></div>
 236 <div class="paragraph"><p>not</p></div>
 237 <div class="listingblock">
 238 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">int</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">bool</span><span class="p">)</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">real</span><span class="w"></span>
 239 </pre></div></div></div>
 240 </li>
 241 </ul></div>
 242 </div>
 243 </div>
 244 <div class="sect1">
 245 <h2 id="_core">Core</h2>
 246 <div class="sectionbody">
 247 <div class="ulist"><ul>
 248 <li>
 249 <p>
 250 A core expression or declaration split over multiple lines does not
 251 contain any blank lines.
 252 </p>
 253 </li>
 254 <li>
 255 <p>
 256 A record field selector has no space between the <span class="monospaced">#</span> and the record
 257 label.  So, write
 258 </p>
 259 <div class="listingblock">
 260 <div class="content"><div class="highlight"><pre><span class="p">#</span><span class="n">foo</span><span class="w"></span>
 261 </pre></div></div></div>
 262 <div class="paragraph"><p>not</p></div>
 263 <div class="listingblock">
 264 <div class="content"><div class="highlight"><pre><span class="p">#</span><span class="w"> </span><span class="n">foo</span><span class="w"></span>
 265 </pre></div></div></div>
 266 </li>
 267 <li>
 268 <p>
 269 A tuple has a space after each comma, but not before, and not at the
 270 delimiters <span class="monospaced">(</span> and <span class="monospaced">)</span>.
 271 </p>
 272 <div class="listingblock">
 273 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">e1</span><span class="p">,</span><span class="w"> </span><span class="n">e2</span><span class="p">,</span><span class="w"> </span><span class="n">e3</span><span class="p">)</span><span class="w"></span>
 274 </pre></div></div></div>
 275 </li>
 276 <li>
 277 <p>
 278 A tuple split over multiple lines has one element per line, and the
 279 commas go at the end of the lines.
 280 </p>
 281 <div class="listingblock">
 282 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">e1</span><span class="p">,</span><span class="w"></span>
 283 <span class="w"> </span><span class="n">e2</span><span class="p">,</span><span class="w"></span>
 284 <span class="w"> </span><span class="n">e3</span><span class="p">)</span><span class="w"></span>
 285 </pre></div></div></div>
 286 </li>
 287 <li>
 288 <p>
 289 A list has a space after each comma, but not before, and not at the
 290 delimiters <span class="monospaced">[</span> and <span class="monospaced">]</span>.
 291 </p>
 292 <div class="listingblock">
 293 <div class="content"><div class="highlight"><pre><span class="p">[</span><span class="n">e1</span><span class="p">,</span><span class="w"> </span><span class="n">e2</span><span class="p">,</span><span class="w"> </span><span class="n">e3</span><span class="p">]</span><span class="w"></span>
 294 </pre></div></div></div>
 295 </li>
 296 <li>
 297 <p>
 298 A list split over multiple lines has one element per line, and the
 299 commas at the end of the lines.
 300 </p>
 301 <div class="listingblock">
 302 <div class="content"><div class="highlight"><pre><span class="p">[</span><span class="n">e1</span><span class="p">,</span><span class="w"></span>
 303 <span class="w"> </span><span class="n">e2</span><span class="p">,</span><span class="w"></span>
 304 <span class="w"> </span><span class="n">e3</span><span class="p">]</span><span class="w"></span>
 305 </pre></div></div></div>
 306 </li>
 307 <li>
 308 <p>
 309 A record has spaces before and after <span class="monospaced">=</span>, a space after each comma,
 310 but not before, and not at the delimiters <span class="monospaced">{</span> and <span class="monospaced">}</span>.  Field names
 311 appear in alphabetical order.
 312 </p>
 313 <div class="listingblock">
 314 <div class="content"><div class="highlight"><pre><span class="p">{</span><span class="n">bar</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="p">,</span><span class="w"> </span><span class="n">foo</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">true</span><span class="p">}</span><span class="w"></span>
 315 </pre></div></div></div>
 316 </li>
 317 <li>
 318 <p>
 319 A sequence expression has a space after each semicolon, but not before.
 320 </p>
 321 <div class="listingblock">
 322 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">e1</span><span class="p">;</span><span class="w"> </span><span class="n">e2</span><span class="p">;</span><span class="w"> </span><span class="n">e3</span><span class="p">)</span><span class="w"></span>
 323 </pre></div></div></div>
 324 </li>
 325 <li>
 326 <p>
 327 A sequence expression split over multiple lines has one expression
 328 per line, and the semicolons at the beginning of lines.  Lisp and
 329 Scheme programmers may find this hard to read at first.
 330 </p>
 331 <div class="listingblock">
 332 <div class="content"><div class="highlight"><pre><span class="p">(</span><span class="n">e1</span><span class="w"></span>
 333 <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 334 <span class="w"> </span><span class="p">;</span><span class="w"> </span><span class="n">e3</span><span class="p">)</span><span class="w"></span>
 335 </pre></div></div></div>
 336 <div class="paragraph"><p><em>Rationale</em>: this makes it easy to visually spot the beginning of each
 337 expression, which becomes more valuable as the expressions themselves
 338 are split across multiple lines.</p></div>
 339 </li>
 340 <li>
 341 <p>
 342 An application expression has a space between the function and the
 343 argument.  There are no parens unless the argument is a tuple (in
 344 which case the parens are really part of the tuple, not the
 345 application).
 346 </p>
 347 <div class="listingblock">
 348 <div class="content"><div class="highlight"><pre><span class="n">f</span><span class="w"> </span><span class="n">a</span><span class="w"></span>
 349 <span class="n">f</span><span class="w"> </span><span class="p">(</span><span class="n">a1</span><span class="p">,</span><span class="w"> </span><span class="n">a2</span><span class="p">,</span><span class="w"> </span><span class="n">a3</span><span class="p">)</span><span class="w"></span>
 350 </pre></div></div></div>
 351 </li>
 352 <li>
 353 <p>
 354 Avoid redundant parentheses.  Application associates to left, so
 355 write
 356 </p>
 357 <div class="listingblock">
 358 <div class="content"><div class="highlight"><pre><span class="n">f</span><span class="w"> </span><span class="n">a1</span><span class="w"> </span><span class="n">a2</span><span class="w"> </span><span class="n">a3</span><span class="w"></span>
 359 </pre></div></div></div>
 360 <div class="paragraph"><p>not</p></div>
 361 <div class="listingblock">
 362 <div class="content"><div class="highlight"><pre><span class="p">((</span><span class="n">f</span><span class="w"> </span><span class="n">a1</span><span class="p">)</span><span class="w"> </span><span class="n">a2</span><span class="p">)</span><span class="w"> </span><span class="n">a3</span><span class="w"></span>
 363 </pre></div></div></div>
 364 </li>
 365 <li>
 366 <p>
 367 Infix operators have a space before and after the operator.
 368 </p>
 369 <div class="listingblock">
 370 <div class="content"><div class="highlight"><pre><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">y</span><span class="w"></span>
 371 <span class="n">x</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">-</span><span class="w"> </span><span class="n">z</span><span class="w"></span>
 372 </pre></div></div></div>
 373 </li>
 374 <li>
 375 <p>
 376 Avoid redundant parentheses.  Use <a href="OperatorPrecedence">OperatorPrecedence</a>.  So, write
 377 </p>
 378 <div class="listingblock">
 379 <div class="content"><div class="highlight"><pre><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">z</span><span class="w"></span>
 380 </pre></div></div></div>
 381 <div class="paragraph"><p>not</p></div>
 382 <div class="listingblock">
 383 <div class="content"><div class="highlight"><pre><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="p">(</span><span class="n">y</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">z</span><span class="p">)</span><span class="w"></span>
 384 </pre></div></div></div>
 385 </li>
 386 <li>
 387 <p>
 388 An <span class="monospaced">andalso</span> expression split over multiple lines has the <span class="monospaced">andalso</span>
 389 at the beginning of subsequent lines.
 390 </p>
 391 <div class="listingblock">
 392 <div class="content"><div class="highlight"><pre><span class="n">e1</span><span class="w"></span>
 393 <span class="k">andalso</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 394 <span class="k">andalso</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 395 </pre></div></div></div>
 396 </li>
 397 <li>
 398 <p>
 399 A <span class="monospaced">case</span> expression is indented as follows
 400 </p>
 401 <div class="listingblock">
 402 <div class="content"><div class="highlight"><pre><span class="k">case</span><span class="w"> </span><span class="n">e1</span><span class="w"> </span><span class="k">of</span><span class="w"></span>
 403 <span class="w">   </span><span class="n">p1</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">e1</span><span class="w"></span>
 404 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">p2</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 405 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">p3</span><span class="w"> </span><span class="p">=&gt;</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 406 </pre></div></div></div>
 407 </li>
 408 <li>
 409 <p>
 410 A <span class="monospaced">datatype</span>'s constructors are alphabetized.
 411 </p>
 412 <div class="listingblock">
 413 <div class="content"><div class="highlight"><pre><span class="k">datatype</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="w"></span>
 414 </pre></div></div></div>
 415 </li>
 416 <li>
 417 <p>
 418 A <span class="monospaced">datatype</span> declaration has a space before and after each <span class="monospaced">|</span>.
 419 </p>
 420 <div class="listingblock">
 421 <div class="content"><div class="highlight"><pre><span class="k">datatype</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">A</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"> </span><span class="k">of</span><span class="w"> </span><span class="n">int</span><span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="w"></span>
 422 </pre></div></div></div>
 423 </li>
 424 <li>
 425 <p>
 426 A <span class="monospaced">datatype</span> split over multiple lines has one constructor per line,
 427 with the <span class="monospaced">|</span> at the beginning of lines and the constructors beginning
 428 3 columns to the right of the <span class="monospaced">datatype</span>.
 429 </p>
 430 <div class="listingblock">
 431 <div class="content"><div class="highlight"><pre><span class="k">datatype</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 432 <span class="w">   </span><span class="n">A</span><span class="w"></span>
 433 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">B</span><span class="w"></span>
 434 <span class="w"> </span><span class="p">|</span><span class="w"> </span><span class="n">C</span><span class="w"></span>
 435 </pre></div></div></div>
 436 </li>
 437 <li>
 438 <p>
 439 A <span class="monospaced">fun</span> declaration may start its body on the subsequent line,
 440 indented 3 spaces.
 441 </p>
 442 <div class="listingblock">
 443 <div class="content"><div class="highlight"><pre><span class="k">fun</span><span class="w"> </span><span class="n">f</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 444 <span class="w">   </span><span class="k">let</span><span class="w"></span>
 445 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">z</span><span class="w"></span>
 446 <span class="w">   </span><span class="k">in</span><span class="w"></span>
 447 <span class="w">      </span><span class="n">z</span><span class="w"></span>
 448 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 449 </pre></div></div></div>
 450 </li>
 451 <li>
 452 <p>
 453 An <span class="monospaced">if</span> expression is indented as follows.
 454 </p>
 455 <div class="listingblock">
 456 <div class="content"><div class="highlight"><pre><span class="k">if</span><span class="w"> </span><span class="n">e1</span><span class="w"></span>
 457 <span class="w">   </span><span class="k">then</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 458 <span class="k">else</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 459 </pre></div></div></div>
 460 </li>
 461 <li>
 462 <p>
 463 A sequence of <span class="monospaced">if</span>-<span class="monospaced">then</span>-<span class="monospaced">else</span>-s is indented as follows.
 464 </p>
 465 <div class="listingblock">
 466 <div class="content"><div class="highlight"><pre><span class="k">if</span><span class="w"> </span><span class="n">e1</span><span class="w"></span>
 467 <span class="w">   </span><span class="k">then</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 468 <span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 469 <span class="w">   </span><span class="k">then</span><span class="w"> </span><span class="n">e4</span><span class="w"></span>
 470 <span class="k">else</span><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="n">e5</span><span class="w"></span>
 471 <span class="w">   </span><span class="k">then</span><span class="w"> </span><span class="n">e6</span><span class="w"></span>
 472 <span class="k">else</span><span class="w"> </span><span class="n">e7</span><span class="w"></span>
 473 </pre></div></div></div>
 474 </li>
 475 <li>
 476 <p>
 477 A <span class="monospaced">let</span> expression has the <span class="monospaced">let</span>, <span class="monospaced">in</span>, and <span class="monospaced">end</span> on their own
 478 lines, starting in the same column.  Declarations and the body are
 479 indented 3 spaces.
 480 </p>
 481 <div class="listingblock">
 482 <div class="content"><div class="highlight"><pre><span class="k">let</span><span class="w"></span>
 483 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 484 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">14</span><span class="w"></span>
 485 <span class="k">in</span><span class="w"></span>
 486 <span class="w">   </span><span class="n">x</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="n">y</span><span class="w"></span>
 487 <span class="k">end</span><span class="w"></span>
 488 </pre></div></div></div>
 489 </li>
 490 <li>
 491 <p>
 492 A <span class="monospaced">local</span> declaration has the <span class="monospaced">local</span>, <span class="monospaced">in</span>, and <span class="monospaced">end</span> on their own
 493 lines, starting in the same column.  Declarations are indented 3
 494 spaces.
 495 </p>
 496 <div class="listingblock">
 497 <div class="content"><div class="highlight"><pre><span class="k">local</span><span class="w"></span>
 498 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 499 <span class="k">in</span><span class="w"></span>
 500 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">x</span><span class="w"></span>
 501 <span class="k">end</span><span class="w"></span>
 502 </pre></div></div></div>
 503 </li>
 504 <li>
 505 <p>
 506 An <span class="monospaced">orelse</span> expression split over multiple lines has the <span class="monospaced">orelse</span> at
 507 the beginning of subsequent lines.
 508 </p>
 509 <div class="listingblock">
 510 <div class="content"><div class="highlight"><pre><span class="n">e1</span><span class="w"></span>
 511 <span class="k">orelse</span><span class="w"> </span><span class="n">e2</span><span class="w"></span>
 512 <span class="k">orelse</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 513 </pre></div></div></div>
 514 </li>
 515 <li>
 516 <p>
 517 A <span class="monospaced">val</span> declaration has a space before and after the <span class="monospaced">=</span>.
 518 </p>
 519 <div class="listingblock">
 520 <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">e</span><span class="w"></span>
 521 </pre></div></div></div>
 522 </li>
 523 <li>
 524 <p>
 525 A <span class="monospaced">val</span> declaration can start the expression on the subsequent line,
 526 indented 3 spaces.
 527 </p>
 528 <div class="listingblock">
 529 <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">p</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 530 <span class="w">   </span><span class="k">if</span><span class="w"> </span><span class="n">e1</span><span class="w"> </span><span class="k">then</span><span class="w"> </span><span class="n">e2</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="n">e3</span><span class="w"></span>
 531 </pre></div></div></div>
 532 </li>
 533 </ul></div>
 534 </div>
 535 </div>
 536 <div class="sect1">
 537 <h2 id="_signatures">Signatures</h2>
 538 <div class="sectionbody">
 539 <div class="ulist"><ul>
 540 <li>
 541 <p>
 542 A <span class="monospaced">signature</span> declaration is indented as follows.
 543 </p>
 544 <div class="listingblock">
 545 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">FOO</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 546 <span class="w">   </span><span class="k">sig</span><span class="w"></span>
 547 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
 548 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 549 </pre></div></div></div>
 550 <div class="paragraph"><p><em>Exception</em>: a signature declaration in a file to itself can omit the
 551 indentation to save horizontal space.</p></div>
 552 <div class="listingblock">
 553 <div class="content"><div class="highlight"><pre><span class="k">signature</span><span class="w"> </span><span class="n">FOO</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 554 <span class="k">sig</span><span class="w"></span>
 555
 556 <span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
 557
 558 <span class="k">end</span><span class="w"></span>
 559 </pre></div></div></div>
 560 <div class="paragraph"><p>In this case, there should be a blank line after the <span class="monospaced">sig</span> and before
 561 the <span class="monospaced">end</span>.</p></div>
 562 </li>
 563 <li>
 564 <p>
 565 A <span class="monospaced">val</span> specification has a space after the colon, but not before.
 566 </p>
 567 <div class="listingblock">
 568 <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
 569 </pre></div></div></div>
 570 <div class="paragraph"><p><em>Exception</em>: in the case of operators (like <span class="monospaced">+</span>), there is a space
 571 before the colon to avoid lexing the colon as part of the operator.</p></div>
 572 <div class="listingblock">
 573 <div class="content"><div class="highlight"><pre><span class="k">val</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="p">:</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="n">*</span><span class="w"> </span><span class="n">t</span><span class="w"> </span><span class="p">-&gt;</span><span class="w"> </span><span class="n">t</span><span class="w"></span>
 574 </pre></div></div></div>
 575 </li>
 576 <li>
 577 <p>
 578 Alphabetize specifications in signatures.
 579 </p>
 580 <div class="listingblock">
 581 <div class="content"><div class="highlight"><pre><span class="k">sig</span><span class="w"></span>
 582 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="p">:</span><span class="w"> </span><span class="n">int</span><span class="w"></span>
 583 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">y</span><span class="p">:</span><span class="w"> </span><span class="n">bool</span><span class="w"></span>
 584 <span class="k">end</span><span class="w"></span>
 585 </pre></div></div></div>
 586 </li>
 587 </ul></div>
 588 </div>
 589 </div>
 590 <div class="sect1">
 591 <h2 id="_structures">Structures</h2>
 592 <div class="sectionbody">
 593 <div class="ulist"><ul>
 594 <li>
 595 <p>
 596 A <span class="monospaced">structure</span> declaration has a space on both sides of the <span class="monospaced">=</span>.
 597 </p>
 598 <div class="listingblock">
 599 <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">Foo</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">Bar</span><span class="w"></span>
 600 </pre></div></div></div>
 601 </li>
 602 <li>
 603 <p>
 604 A <span class="monospaced">structure</span> declaration split over multiple lines is indented as
 605 follows.
 606 </p>
 607 <div class="listingblock">
 608 <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 609 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 610 <span class="w">      </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 611 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 612 </pre></div></div></div>
 613 <div class="paragraph"><p><em>Exception</em>: a structure declaration in a file to itself can omit the
 614 indentation to save horizontal space.</p></div>
 615 <div class="listingblock">
 616 <div class="content"><div class="highlight"><pre><span class="k">structure</span><span class="w"> </span><span class="n">S</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 617 <span class="k">struct</span><span class="w"></span>
 618
 619 <span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 620
 621 <span class="k">end</span><span class="w"></span>
 622 </pre></div></div></div>
 623 <div class="paragraph"><p>In this case, there should be a blank line after the <span class="monospaced">struct</span> and
 624 before the <span class="monospaced">end</span>.</p></div>
 625 </li>
 626 <li>
 627 <p>
 628 Declarations in a <span class="monospaced">struct</span> are separated by blank lines.
 629 </p>
 630 <div class="listingblock">
 631 <div class="content"><div class="highlight"><pre><span class="k">struct</span><span class="w"></span>
 632 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 633 <span class="w">      </span><span class="k">let</span><span class="w"></span>
 634 <span class="w">         </span><span class="n">y</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">13</span><span class="w"></span>
 635 <span class="w">      </span><span class="k">in</span><span class="w"></span>
 636 <span class="w">         </span><span class="n">y</span><span class="w"> </span><span class="n">+</span><span class="w"> </span><span class="mi">1</span><span class="w"></span>
 637 <span class="w">      </span><span class="k">end</span><span class="w"></span>
 638
 639 <span class="w">   </span><span class="k">val</span><span class="w"> </span><span class="n">z</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="mi">14</span><span class="w"></span>
 640 <span class="k">end</span><span class="w"></span>
 641 </pre></div></div></div>
 642 </li>
 643 </ul></div>
 644 </div>
 645 </div>
 646 <div class="sect1">
 647 <h2 id="_functors">Functors</h2>
 648 <div class="sectionbody">
 649 <div class="ulist"><ul>
 650 <li>
 651 <p>
 652 A <span class="monospaced">functor</span> declaration has spaces after each <span class="monospaced">:</span> (or <span class="monospaced">:&gt;</span>) but not
 653 before, and a space before and after the <span class="monospaced">=</span>.  It is indented as
 654 follows.
 655 </p>
 656 <div class="listingblock">
 657 <div class="content"><div class="highlight"><pre><span class="k">functor</span><span class="w"> </span><span class="n">Foo</span><span class="w"> </span><span class="p">(</span><span class="n">S</span><span class="p">:</span><span class="w"> </span><span class="n">FOO_ARG</span><span class="p">):</span><span class="w"> </span><span class="n">FOO</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 658 <span class="w">   </span><span class="k">struct</span><span class="w"></span>
 659 <span class="w">       </span><span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="p">.</span><span class="n">x</span><span class="w"></span>
 660 <span class="w">   </span><span class="k">end</span><span class="w"></span>
 661 </pre></div></div></div>
 662 <div class="paragraph"><p><em>Exception</em>: a functor declaration in a file to itself can omit the
 663 indentation to save horizontal space.</p></div>
 664 <div class="listingblock">
 665 <div class="content"><div class="highlight"><pre><span class="k">functor</span><span class="w"> </span><span class="n">Foo</span><span class="w"> </span><span class="p">(</span><span class="n">S</span><span class="p">:</span><span class="w"> </span><span class="n">FOO_ARG</span><span class="p">):</span><span class="w"> </span><span class="n">FOO</span><span class="w"> </span><span class="p">=</span><span class="w"></span>
 666 <span class="k">struct</span><span class="w"></span>
 667
 668 <span class="k">val</span><span class="w"> </span><span class="n">x</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="n">S</span><span class="p">.</span><span class="n">x</span><span class="w"></span>
 669
 670 <span class="k">end</span><span class="w"></span>
 671 </pre></div></div></div>
 672 <div class="paragraph"><p>In this case, there should be a blank line after the <span class="monospaced">struct</span>
 673 and before the <span class="monospaced">end</span>.</p></div>
 674 </li>
 675 </ul></div>
 676 </div>
 677 </div>
 678 </div>
 679 <div id="footnotes"><hr></div>
 680 <div id="footer">
 681 <div id="footer-text">
 682 </div>
 683 <div id="footer-badges">
 684 </div>
 685 </div>
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