spec: explicitly define integer, floating-point, and complex types

The terms "integer type", "floating-point type", and "complex type"
are used frequently in the spec but are not explicitly (only indirectly)
defined.

Slightly rephrased the section on numeric types and introduce these
terms explicitly. Add links to this section.

Change-Id: I3fb888933bece047da8b356b684c855618e9aee4
Reviewed-on: https://go-review.googlesource.com/c/go/+/384157
Trust: Robert Griesemer <gri@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

doc/go_spec.html

@@ -1,6 +1,6 @@
 <!--{
 	"Title": "The Go Programming Language Specification - Go 1.18 Draft (incomplete)",
-	"Subtitle": "Version of Jan 31, 2022",
+	"Subtitle": "Version of Feb 8, 2022",
 	"Path": "/ref/spec"
 }-->
 
@@ -901,7 +901,9 @@ it is a <a href="#Type_definitions">defined type</a>.
 <h3 id="Numeric_types">Numeric types</h3>
 
 <p>
-A <i>numeric type</i> represents sets of integer or floating-point values.
+An <i>integer</i>, <i>floating-point</i>, or <i>complex</i> type
+represents the set of integer, floating-point, or complex values, respectively.
+They are collectively called <i>numeric types</i>.
 The predeclared architecture-independent numeric types are:
 </p>
 
@@ -932,7 +934,7 @@ The value of an <i>n</i>-bit integer is <i>n</i> bits wide and represented using
 </p>
 
 <p>
-There is also a set of predeclared numeric types with implementation-specific sizes:
+There is also a set of predeclared integer types with implementation-specific sizes:
 </p>
 
 <pre class="grammar">
@@ -1921,7 +1923,7 @@ if one of the following conditions applies:
 </li>
 
 <li>
-<code>T</code> is a floating-point type and <code>x</code> can be rounded to <code>T</code>'s
+<code>T</code> is a <a href="#Numeric_types">floating-point type</a> and <code>x</code> can be rounded to <code>T</code>'s
 precision without overflow. Rounding uses IEEE 754 round-to-even rules but with an IEEE
 negative zero further simplified to an unsigned zero. Note that constant values never result
 in an IEEE negative zero, NaN, or infinity.
@@ -3108,7 +3110,7 @@ For array and slice literals the following rules apply:
 	    key must be a non-negative constant
 	    <a href="#Representability">representable</a> by
 	    a value of type <code>int</code>; and if it is typed
-	    it must be of integer type.
+	    it must be of <a href="#Numeric_types">integer type</a>.
 	</li>
 	<li>An element without a key uses the previous element's index plus one.
 	    If the first element has no key, its index is zero.
@@ -3707,7 +3709,7 @@ The following rules apply:
 If <code>a</code> is not a map:
 </p>
 <ul>
-	<li>the index <code>x</code> must be of integer type or an untyped constant</li>
+	<li>the index <code>x</code> must be of <a href="#Numeric_types">integer type</a> or an untyped constant</li>
 	<li>a constant index must be non-negative and
 	    <a href="#Representability">representable</a> by a value of type <code>int</code></li>
 	<li>a constant index that is untyped is given type <code>int</code></li>
@@ -4660,7 +4662,7 @@ to the type of the other operand.
 </p>
 
 <p>
-The right operand in a shift expression must have integer type
+The right operand in a shift expression must have <a href="#Numeric_types">integer type</a>
 or be an untyped constant <a href="#Representability">representable</a> by a
 value of type <code>uint</code>.
 If the left operand of a non-constant shift expression is an untyped constant,
@@ -4740,8 +4742,9 @@ x == y+1 &amp;&amp; &lt;-chanInt &gt; 0
 <p>
 Arithmetic operators apply to numeric values and yield a result of the same
 type as the first operand. The four standard arithmetic operators (<code>+</code>,
-<code>-</code>, <code>*</code>, <code>/</code>) apply to integer,
-floating-point, and complex types; <code>+</code> also applies to strings.
+<code>-</code>, <code>*</code>, <code>/</code>) apply to
+<a href="#Numeric_types">integer</a>, <a href="#Numeric_types">floating-point</a>, and
+<a href="#Numeric_types">complex</a> types; <code>+</code> also applies to <a href="#String_types">strings</.
 The bitwise logical and shift operators apply to integers only.
 </p>
 
@@ -4880,7 +4883,7 @@ occurs is implementation-specific.
 An implementation may combine multiple floating-point operations into a single
 fused operation, possibly across statements, and produce a result that differs
 from the value obtained by executing and rounding the instructions individually.
-An explicit floating-point type <a href="#Conversions">conversion</a> rounds to
+An explicit <a href="#Numeric_types">floating-point type</a> <a href="#Conversions">conversion</a> rounds to
 the precision of the target type, preventing fusion that would discard that rounding.
 </p>
 
@@ -5321,19 +5324,19 @@ For the conversion of non-constant numeric values, the following rules apply:
 
 <ol>
 <li>
-When converting between integer types, if the value is a signed integer, it is
+When converting between <a href="#Numeric_types">integer types</a>, if the value is a signed integer, it is
 sign extended to implicit infinite precision; otherwise it is zero extended.
 It is then truncated to fit in the result type's size.
 For example, if <code>v := uint16(0x10F0)</code>, then <code>uint32(int8(v)) == 0xFFFFFFF0</code>.
 The conversion always yields a valid value; there is no indication of overflow.
 </li>
 <li>
-When converting a floating-point number to an integer, the fraction is discarded
+When converting a <a href="#Numeric_types">floating-point number</a> to an integer, the fraction is discarded
 (truncation towards zero).
 </li>
 <li>
 When converting an integer or floating-point number to a floating-point type,
-or a complex number to another complex type, the result value is rounded
+or a <a href="#Numeric_types">complex number</a> to another complex type, the result value is rounded
 to the precision specified by the destination type.
 For instance, the value of a variable <code>x</code> of type <code>float32</code>
 may be stored using additional precision beyond that of an IEEE-754 32-bit number,
@@ -7037,7 +7040,7 @@ make(T, n)       channel    buffered channel of type T, buffer size n
 
 
 <p>
-Each of the size arguments <code>n</code> and <code>m</code> must be of integer type
+Each of the size arguments <code>n</code> and <code>m</code> must be of <a href="#Numeric_types">integer type</a>
 or an untyped <a href="#Constants">constant</a>.
 A constant size argument must be non-negative and <a href="#Representability">representable</a>
 by a value of type <code>int</code>; if it is an untyped constant it is given type <code>int</code>.
@@ -7182,7 +7185,8 @@ imag(complexT) floatT
 <p>
 The type of the arguments and return value correspond.
 For <code>complex</code>, the two arguments must be of the same
-floating-point type and the return type is the complex type
+<a href="#Numeric_types">floating-point type</a> and the return type is the
+<a href="#Numeric_types">complex type</a>
 with the corresponding floating-point constituents:
 <code>complex64</code> for <code>float32</code> arguments, and
 <code>complex128</code> for <code>float64</code> arguments.
@@ -7897,7 +7901,7 @@ of constant size.
 <p>
 The function <code>Add</code> adds <code>len</code> to <code>ptr</code>
 and returns the updated pointer <code>unsafe.Pointer(uintptr(ptr) + uintptr(len))</code>.
-The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>.
+The <code>len</code> argument must be of <a href="#Numeric_types">integer type</a> or an untyped <a href="#Constants">constant</a>.
 A constant <code>len</code> argument must be <a href="#Representability">representable</a> by a value of type <code>int</code>;
 if it is an untyped constant it is given type <code>int</code>.
 The rules for <a href="/pkg/unsafe#Pointer">valid uses</a> of <code>Pointer</code> still apply.
@@ -7920,7 +7924,7 @@ is <code>nil</code> and <code>len</code> is zero,
 </p>
 
 <p>
-The <code>len</code> argument must be of integer type or an untyped <a href="#Constants">constant</a>.
+The <code>len</code> argument must be of <a href="#Numeric_types">integer type</a> or an untyped <a href="#Constants">constant</a>.
 A constant <code>len</code> argument must be non-negative and <a href="#Representability">representable</a> by a value of type <code>int</code>;
 if it is an untyped constant it is given type <code>int</code>.
 At run time, if <code>len</code> is negative,