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<body class="article">
<div id="header">
<h1>Specifications of SigScheme</h1>
</div>
<div id="content">
<div class="sect1">
<h2 id="_general">1. General</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_64_bit_data_models">1.1. 64-bit data models</h3>
<div class="paragraph"><p>Supports LL64, LLP64, LP64 and ILP64 on both storage-fatty and storage-compact.</p></div>
</div>
<div class="sect2">
<h3 id="_addressable_memory_space">1.2. Addressable memory space</h3>
<div class="paragraph"><p>Ordinary storage implementation can address any Scheme object scattered on
whole memory space. Both storage-fatty and storage-compact have no
limitation on any 32 and 64-bit data models. But it may be limited if a
storage implementation is designed to do so for some specific advantages,
as like GNU Emacs' 28-bit tagged pointer does.</p></div>
</div>
<div class="sect2">
<h3 id="_integer_range">1.3. Integer range</h3>
<div class="paragraph"><p>Current implementation only supports fixnum, and its range varies by the
user-selected underlying storage implementation. The range can be known via
R6RS (R5.91RS) compatible <code>(fixnum-width)</code>, <code>(least-fixnum)</code> and
<code>(greatest-fixnum)</code>.</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_r5rs_conformance">2. R5RS conformance</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_proper_tail_recursion">2.1. Proper tail recursion</h3>
<div class="paragraph"><p>Supported. But the conformance of <code>eval</code> procedure is uncertain. See the
comments of <code>scm_p_eval()</code> and <code>rec-by-eval</code> of <code>test-tail-rec.scm</code> for further
information about <code>eval</code>.</p></div>
</div>
<div class="sect2">
<h3 id="_continuations">2.2. Continuations</h3>
<div class="paragraph"><p>Limited to nested use due to its setjmp/longjmp implementation. If a
continuation that is not an ancestor of current continuation called, all
continuation objects lying between the curent and the common ancestor of
the destination are invalidated. Calling an invalidated continuation object
causes an error.</p></div>
</div>
<div class="sect2">
<h3 id="_hygienic_macros">2.3. Hygienic macros</h3>
<div class="paragraph"><p>The hygienic macros are fully supported. But although the macro expansion
engine itself works well and can be expected as R5RS-conformant, its
integration into SigScheme is not fully validated yet. It is likely having a
problem on identifier references. So the feature is disabled by default on most
configurations.</p></div>
<div class="paragraph"><p>In addition to the validity problem, there is an architectural inefficiency.
Since SigScheme development had been started as macro-less naive system, it
lacks the concepts <em>compilation</em>, <em>macro-expansion phase</em> and <em>lexical
environment</em>. So current SigScheme implementation adopted runtime macro
expansion. A macro form is kept untransformed in program, and expanded
immediately before each evaluation. For example, following code causes macro
expansion on each <code>map-caddr</code> call.</p></div>
<div class="listingblock">
<div class="title">Macro expansion inefficiency</div>
<div class="content">
<pre><code>(define-syntax compose-internal
  (syntax-rules ()
    ((compose-internal f x)     (f x))
    ((compose-internal f g ...) (f (compose-internal g ...)))))

(define-syntax compose
  (syntax-rules ()
    ((compose)         values)
    ((compose f)       f)
    ((compose f g ...) (lambda (x) (compose-internal f g ... x)))))

(define map-caddr
  (lambda (lst)
    (map (compose car cdr cdr) lst)))</code></pre>
</div></div>
<div class="paragraph"><p>Since it is considerably inefficient in many cases, keep in mind the expansion
cost. The inefficiency problem is expected to be resolved in SigScheme 0.9.0.</p></div>
</div>
<div class="sect2">
<h3 id="_numbers">2.4. Numbers</h3>
<div class="paragraph"><p>SigScheme supports only the integer part of the numerical tower.</p></div>
<div class="sect3">
<h4 id="_literals">2.4.1. Literals</h4>
<div class="paragraph"><p>SigScheme recognizes only these limited part of numerical forms of "7.1.1
Lexical structure" section of R5RS. Other valid R5RS forms for numbers produce
errors.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  &lt;number&gt; --&gt; &lt;num 2&gt;| &lt;num 8&gt;
       | &lt;num 10&gt;| &lt;num 16&gt;

  &lt;num R&gt; --&gt; &lt;prefix R&gt; &lt;complex R&gt;
  &lt;complex R&gt; --&gt; &lt;real R&gt;
  &lt;real R&gt; --&gt; &lt;sign&gt; &lt;ureal R&gt;
  &lt;ureal R&gt; --&gt; &lt;uinteger R&gt;
  &lt;uinteger R&gt; --&gt; &lt;digit R&gt;+ #*   ;; '#' must not occur
  &lt;prefix R&gt; --&gt; &lt;radix R&gt;

  &lt;sign&gt; --&gt; &lt;empty&gt;  | + |  -
  &lt;radix 2&gt; --&gt; #b
  &lt;radix 8&gt; --&gt; #o
  &lt;radix 10&gt; --&gt; &lt;empty&gt; | #d
  &lt;radix 16&gt; --&gt; #x
  &lt;digit 2&gt; --&gt; 0 | 1
  &lt;digit 8&gt; --&gt; 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7
  &lt;digit 10&gt; --&gt; &lt;digit&gt;
  &lt;digit 16&gt; --&gt; &lt;digit 10&gt; | a | b | c | d | e | f
  &lt;digit&gt; --&gt; 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9</code></pre>
</div></div>
<div class="paragraph"><p>SigScheme accepts only lower case alphabets as radices as follows. But
hexadecimal digits can be written as either lower or upper.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  #b11  ==&gt;  3
  #B11  ==&gt;  error
  #xa1  ==&gt;  161
  #Xa1  ==&gt;  error
  #xAb  ==&gt;  171</code></pre>
</div></div>
<div class="paragraph"><p>SigScheme uses a fixed-size buffer for number literals parsing. Due to the
implementation, it can accept only one optional <em>0</em> prefix for maximum-length
binary number literals. Two or more <em>0</em> prefixes causes an error as follows.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  ;; storage-compact on ILP32 env

  (greatest-fixnum)                      ==&gt; 2147483647
  #b11111111000000001111111100000000     ==&gt; 4278255360
  #b011111111000000001111111100000000    ==&gt; 4278255360
  #b0011111111000000001111111100000000   ==&gt; error
  #b00011111111000000001111111100000000  ==&gt; error</code></pre>
</div></div>
</div>
<div class="sect3">
<h4 id="_optional_procedures">2.4.2. Optional procedures</h4>
<div class="paragraph"><p>The procedures <em>-</em> and <em>/</em> support following optional form.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  6.2.5 Numerical operations

  optional procedure: - z1 z2 ...
  optional procedure: / z1 z2 ...</code></pre>
</div></div>
</div>
</div>
<div class="sect2">
<h3 id="_characters">2.5. Characters</h3>
<div class="paragraph"><p>All character category-sensitive procedures and predicates (such as
char-upcase) work correctly only in ASCII range. i.e. Neither Unicode
processing specified in R6RS nor other non-Unicode multibyte character
processing are supported in such procedures/predicates.</p></div>
</div>
<div class="sect2">
<h3 id="_non_ascii_charcter_acceptance">2.6. Non-ASCII charcter acceptance</h3>
<div class="paragraph"><p><code>integer-&gt;char</code> only accepts valid characters of current character codec. If
no multibyte character codec is enabled on configuration, it accepts 0-255.</p></div>
<div class="paragraph"><p>If no multibyte character codec is enabled on configuration, character
literal only covers ASCII.</p></div>
<div class="paragraph"><p>If UTF-8 codec is enabled and is the current codec, character literal covers
all valid Unicode charcters.</p></div>
</div>
<div class="sect2">
<h3 id="_whitespace_charcters">2.7. Whitespace charcters</h3>
<div class="paragraph"><p>SigScheme treats vertical tab (0x0b) as a white space charcter although
R5RS <code>char-whitespace?</code> does not cover it.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  R5RS: 6.3.4 Characters

  The whitespace characters are space, tab, line feed, form feed, and
  carriage return.</code></pre>
</div></div>
<div class="listingblock">
<div class="content">
<pre><code>  R6RS Standard Libraries: 1.1  Characters

  A character is whitespace if it is in one of the space, line, or
  paragraph separator categories (Zs, Zl or Zp), or if is U+0009
  (Horizontal tabulation), U+000A (Line feed), U+000B (Vertical
  tabulation), U+000C (Form feed), or U+000D (Carriage return).</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_case_insensitive_character_comparison">2.8. Case-insensitive character comparison</h3>
<div class="paragraph"><p>SigScheme&#8217;s case-insensitive comparison conforms to the foldcase&#8217;ed
comparison described in R6RS and SRFI-13, although R5RS does not specify
comparison between alphabetic and non-alphabetic char.</p></div>
<div class="paragraph"><p>See the description in sigschemeinternal.h for further details.</p></div>
</div>
<div class="sect2">
<h3 id="_case_sensitive_identifiers">2.9. Case-sensitive identifiers</h3>
<div class="paragraph"><p>SigScheme does distinguish letter case in indentifiers. Although case
insensitivity is required in R5RS as follows, it is hard to accept for the
our application.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  2. Lexical conventions

  Upper and lower case forms of a letter are never distinguished except
  within character and string constants. For example, `Foo' is the same
  identifier as `FOO', and #x1AB is the same number as #X1ab.</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_constant_string">2.10. Constant string</h3>
<div class="paragraph"><p>SigScheme treats string literals as constant as specified in R5RS.</p></div>
<div class="exampleblock">
<div class="title">Example 1. constant string</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (string-set! "foo" 0 #\F)
Error: in string-set!: attempted to modify immutable string: "foo"</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (string-set! (string-copy "foo") 0 #\F)
"Foo"</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_constant_list">2.11. Constant list</h3>
<div class="paragraph"><p>SigScheme inhibits modification of constant list object by default as
specified in R5RS, if the storage implementation suports it. storage-fatty
supports it, but storage-compact does not due to no bit space for pair
object.</p></div>
<div class="paragraph"><p>The behavior can be changed by <code>SCM_CONST_LIST_LITERAL</code>.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  4.1.2 Literal expressions

      `(quote &lt;datum&gt;)' may be abbreviated as '&lt;datum&gt;. The two notations
      are equivalent in all respects.

      'a                                     ==&gt;  a
      '#(a b c)                              ==&gt;  #(a b c)
      '()                                    ==&gt;  ()
      '(+ 1 2)                               ==&gt;  (+ 1 2)
      '(quote a)                             ==&gt;  (quote a)
      ''a                                    ==&gt;  (quote a)

      As noted in section 3.4 Storage model, it is an error to alter a
      constant (i.e. the value of a literal expression) using a mutation
      procedure like `set-car!' or `string-set!'.

  6.3.2 Pairs and lists

  procedure: set-car! pair obj

      Stores obj in the car field of pair. The value returned by `set-car!'
      is unspecified.

      (define (g) '(constant-list))
      (set-car! (g) 3)                       ==&gt;  error</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_constant_vector">2.12. Constant vector</h3>
<div class="paragraph"><p>SigScheme inhibits modification of constant vector object by default as
specified in R5RS, if the storage implementation suports it. storage-fatty
supports it, but storage-compact is not yet.</p></div>
<div class="paragraph"><p>The behavior can be changed by <code>SCM_CONST_VECTOR_LITERAL</code>.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  6.3.6 Vectors

  procedure: vector-set! vector k obj

      (vector-set! '#(0 1 2) 1 "doe")
                ==&gt;  error  ; constant vector</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_quote_less_null_list">2.13. Quote-less null list</h3>
<div class="paragraph"><p>SigScheme allows quote-less null list by default for convenience and
performance. But it can be error as specified in R5RS, when <code>SCM_STRICT_R5RS</code>
is enabled.</p></div>
<div class="exampleblock">
<div class="title">Example 2. SCM_STRICT_R5RS disabled</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (null? ())
#t</code></pre>
</div></div>
</div></div>
<div class="exampleblock">
<div class="title">Example 3. SCM_STRICT_R5RS enabled</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (null? ())
Error: eval: () is not a valid R5RS form. use '() instead</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_quote_less_vector_literal">2.14. Quote-less vector literal</h3>
<div class="paragraph"><p>Sigscheme inhibits quote-less vector literal by default, as specified in
R5RS.</p></div>
<div class="paragraph"><p>The behavior can be changed by <code>SCM_STRICT_VECTOR_FORM</code>.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  6.3.6 Vectors

  Vectors are written using the notation #(obj ...). For example, a vector
  of length 3 containing the number zero in element 0, the list `(2 2 2 2)'
  in element 1, and the string `"Anna"' in element 2 can be written as
  following:

  #(0 (2 2 2 2) "Anna")

  Note that this is the external representation of a vector, not an
  expression evaluating to a vector. Like list constants, vector constants
  must be quoted:

  '#(0 (2 2 2 2) "Anna")
            ==&gt;  #(0 (2 2 2 2) "Anna")</code></pre>
</div></div>
<div class="exampleblock">
<div class="title">Example 4. vector literals</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; #(1 2 3)
Error: eval: #() is not a valid R5RS form. use '#() instead
sscm&gt; '#(1 2 3)
#(1 2 3)</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_environment_specifiers">2.15. Environment specifiers</h3>
<div class="paragraph"><p><code>(null-environment)</code> and <code>(scheme-report-environment)</code> does not return correct
environemnt specified in R5RS. Current implementation returns same object
of <code>(interaction-environment)</code>.</p></div>
</div>
<div class="sect2">
<h3 id="_internal_definitions">2.16. Internal definitions</h3>
<div class="paragraph"><p>SigScheme strictly conforms to the <em>internal definitions</em> defined in R5RS
(cited below) if <code>SCM_STRICT_DEFINE_PLACEMENT</code> is enabled (default). It can be
disabled to get the syntax loosen, shrink the footprint and reduce runtime
cost.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  5.2.2 Internal definitions

  Definitions may occur at the beginning of a &lt;body&gt; (that is, the body of a
  lambda, let, let*, letrec, let-syntax, or letrec-syntax expression or that of
  a definition of an appropriate form). Such definitions are known as internal
  definitions as opposed to the top level definitions described above.</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_superfluous_arguments">2.17. Superfluous arguments</h3>
<div class="paragraph"><p>Superfluous or dotted arguments are strictly rejected as an error if
<code>SCM_STRICT_ARGCHECK</code> is enabled. Otherwise ignored. Resource-sensitive
apprication could disable it.</p></div>
<div class="exampleblock">
<div class="title">Example 5. SCM_STRICT_ARGCHECK enabled</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (car '(1 2) 3 4)
Error: in (function call): superfluous argument(s): (3 4)
sscm&gt; (symbol? 'foo . #t)
Error: in (function call): improper argument list terminator: #t
sscm&gt; (+ 3 4 . 5)
Error: in (reduction): improper argument list terminator: 5</code></pre>
</div></div>
</div></div>
<div class="exampleblock">
<div class="title">Example 6. SCM_STRICT_ARGCHECK disabled</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (car '(1 2) 3 4)
1
sscm&gt; (symbol? 'foo . #t)
#t
sscm&gt; (+ 3 4 . 5)
7</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_promises">2.18. Promises</h3>
<div class="paragraph"><p>SigScheme only supports explicit forcing. And passing non-promise objects to
force is an error.</p></div>
<div class="listingblock">
<div class="content">
<pre><code>  (+ (delay (* 3 7)) 13)            ==&gt;  error</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_syntaxes_procedures_not_implemented">2.19. Syntaxes/procedures not implemented</h3>
<div class="paragraph"><p>Following R5RS syntaxes and procedures are not implemented (yet).</p></div>
<div class="sect3">
<h4 id="_numbers_2">2.19.1. Numbers</h4>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> complex? obj
</p>
</li>
<li>
<p>
<strong>procedure:</strong> real? obj
</p>
</li>
<li>
<p>
<strong>procedure:</strong> rational? obj
</p>
</li>
<li>
<p>
<strong>procedure:</strong> exact? z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> inexact? z
</p>
</li>
<li>
<p>
<strong>library procedure:</strong> gcd n1 &#8230;
</p>
</li>
<li>
<p>
<strong>library procedure:</strong> lcm n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> numerator q
</p>
</li>
<li>
<p>
<strong>procedure:</strong> denominator q
</p>
</li>
<li>
<p>
<strong>procedure:</strong> floor x
</p>
</li>
<li>
<p>
<strong>procedure:</strong> ceiling x
</p>
</li>
<li>
<p>
<strong>procedure:</strong> truncate x
</p>
</li>
<li>
<p>
<strong>procedure:</strong> round x
</p>
</li>
<li>
<p>
<strong>library procedure:</strong> rationalize x y
</p>
</li>
<li>
<p>
<strong>procedure:</strong> exp z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> log z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> sin z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> cos z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> tan z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> asin z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> acos z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> atan z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> atan y x
</p>
</li>
<li>
<p>
<strong>procedure:</strong> sqrt z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> expt z1 z2
</p>
</li>
<li>
<p>
<strong>procedure:</strong> make-rectangular x1 x2
</p>
</li>
<li>
<p>
<strong>procedure:</strong> make-polar x3 x4
</p>
</li>
<li>
<p>
<strong>procedure:</strong> real-part z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> imag-part z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> magnitude z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> angle z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> exact&#8594;inexact z
</p>
</li>
<li>
<p>
<strong>procedure:</strong> inexact&#8594;exact z
</p>
</li>
</ul></div>
</div>
<div class="sect3">
<h4 id="_system_interface">2.19.2. System interface</h4>
<div class="ulist"><ul>
<li>
<p>
<strong>optional procedure:</strong> transcript-on filename
</p>
</li>
<li>
<p>
<strong>optional procedure:</strong> transcript-off
</p>
</li>
</ul></div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_srfi_conformance">3. SRFI conformance</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_srfi_0_feature_based_conditional_expansion_construct">3.1. SRFI-0  Feature-based conditional expansion construct</h3>
<div class="paragraph"><p>Supported. But since the macro expansion is performed at evaluation-time and
the expanded form is not stored as the code, the form may be expanded
differently at next time.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_1_list_library">3.2. SRFI-1  List Library</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>It is based on the reference implementation of SRFI-1. Some procedures are
replaced with efficient C implementation. And bugs in <code>delete-duplicates!</code>,
<code>lset-xor</code>, <code>lset-xor!</code> and <code>list=</code> of the reference implementation are fixed.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_2_and_let">3.3. SRFI-2 AND-LET*</h3>
<div class="paragraph"><p>Fully supported.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_6_basic_string_ports">3.4. SRFI-6 Basic String Ports</h3>
<div class="paragraph"><p>Fully supported.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_8_receive">3.5. SRFI-8 receive</h3>
<div class="paragraph"><p>Fully supported.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_9_defining_record_types">3.6. SRFI-9 Defining Record Types</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>It is based on the reference implementation of SRFI-9. But different to the
original implementation, <code>eval</code> procedure of the SigScheme port accepts
<code>(interaction-environment)</code> as environment argument.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_22_running_scheme_scripts_on_unix">3.7. SRFI-22 Running Scheme Scripts on Unix</h3>
<div class="paragraph"><p>SigScheme only supports the prelude line interpretation. All options written in
the line are applied as same as commandline invocation of sscm. But the <code>main</code>
procedure invocation is not supported (yet).</p></div>
<div class="exampleblock">
<div class="title">Example 7. Prelude line is interpreted as follows</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>#! /usr/bin/env sscm -C UTF-8
...</code></pre>
</div></div>
<div class="literalblock">
<div class="content">
<pre><code>==&gt; Character encoding for the file is changed to UTF-8 temporarily.</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_srfi_23_error_reporting_mechanism">3.8. SRFI-23 Error Reporting Mechanism</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>If srfi-34 is provided, the <code>error</code> procedure throws a SigScheme-specific error
object in cooperate with "SRFI-34 Exception Handling for Programs". Otherwise
it simply calls scm_fatal_error(). Since the error objects are represented as a
list, be careful on catching an exception based on its type.  If you want to
distinguish the error objects from ordinary lists, use SigScheme-specific
<code>%%error-object?</code> predicate.</p></div>
<div class="exampleblock">
<div class="title">Example 8. Error objects are also caught as a list</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (guard (obj ((pair? obj) obj)) (error "reason" 1 2 3))
#&lt;error "reason" 1 2 3&gt;</code></pre>
</div></div>
</div></div>
<div class="exampleblock">
<div class="title">Example 9. Error object internal</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (define err (guard (err (#t err)) (error "reason" 1 2 3)))
err
sscm&gt; err
#&lt;error "reason" 1 2 3&gt;
sscm&gt; (pair? err)
#t
sscm&gt; (car err)
(#&lt;undef&gt; . #&lt;undef&gt;)
sscm&gt; (%%error-object? err)
#t</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_srfi_28_basic_format_strings">3.9. SRFI-28 Basic Format Strings</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>A directive-less tilde at end of a format string causes an error as same as the
reference implementation of SRFI-28.</p></div>
<div class="exampleblock">
<div class="title">Example 10. SigScheme</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>(format "~")   ==&gt; error
(format "a~")  ==&gt; error</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_srfi_34_exception_handling_for_programs">3.10. SRFI-34 Exception Handling for Programs</h3>
<div class="paragraph"><p>Fully supported.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_38_external_representation_for_data_with_shared_structure">3.11. SRFI-38 External Representation for Data with Shared Structure</h3>
<div class="paragraph"><p>Only <code>write-with-shared-structure</code> is implemented and
<code>read-with-shared-structure</code> is not. The optional alias <code>write/ss</code> described in
SRFI-38 is also defined. The optional <code>optarg</code> argument is simply ignored.</p></div>
<div class="paragraph"><p>The shared index starts with #1 (not #0).</p></div>
<div class="exampleblock">
<div class="title">Example 11. Shared index starts with #1</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>sscm&gt; (define lst (list 'a 'b))
lst
sscm&gt; (set-cdr! lst lst)
#1=(a . #1#)
sscm&gt; lst
#1=(a . #1#)</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_srfi_43_vector_library">3.12. SRFI-43 Vector library</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>It is based on the reference implementation of SRFI-43.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_48_intermediate_format_strings">3.13. SRFI-48 Intermediate Format Strings</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>The <em>d</em> part of <em>~w,dF</em> directive is acceptable, but completely ignored on
output format. Since SigScheme only supports integer currently, number is
always formatted as integer even if the <em>d</em> part is specified.</p></div>
<div class="exampleblock">
<div class="title">Example 12. Proper behavior</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>(format "~3F"   3)  ==&gt; "  3"
(format "~3,2F" 3)  ==&gt; "3.00"</code></pre>
</div></div>
</div></div>
<div class="exampleblock">
<div class="title">Example 13. SigScheme</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>(format "~3F"   3)  ==&gt; "  3"
(format "~3,2F" 3)  ==&gt; "  3"</code></pre>
</div></div>
</div></div>
<div class="paragraph"><p>Although the reference implementation of SRFI-48 allows directive-less tilde at
end of a format string, SigScheme rejects it as an error since it decreases
user-code portability, and is confusable due to that the behavior is different
to the reference implementation of SRFI-28.</p></div>
<div class="exampleblock">
<div class="title">Example 14. Reference implementation of SRFI-48</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>(format "~")   ==&gt; "~"
(format "a~")  ==&gt; "a~"</code></pre>
</div></div>
</div></div>
<div class="exampleblock">
<div class="title">Example 15. SigScheme</div>
<div class="content">
<div class="literalblock">
<div class="content">
<pre><code>(format "~")   ==&gt; error
(format "a~")  ==&gt; error</code></pre>
</div></div>
</div></div>
</div>
<div class="sect2">
<h3 id="_srfi_55_require_extension">3.14. SRFI-55 require-extension</h3>
<div class="paragraph"><p>Fully supported.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_60_integer_as_bits">3.15. SRFI-60 Integer as Bits</h3>
<div class="paragraph"><p>Only following procedures are implemented.</p></div>
<div class="ulist"><ul>
<li>
<p>
Bitwise Operations
</p>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> logand n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-and n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> logior n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-ior n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> logxor n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-xor n1 &#8230;
</p>
</li>
<li>
<p>
<strong>procedure:</strong> lognot n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-not n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-if mask n0 n1
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bitwise-merge mask n0 n1
</p>
</li>
<li>
<p>
<strong>procedure:</strong> logtest j k
</p>
</li>
<li>
<p>
<strong>procedure:</strong> any-bits-set? j k
</p>
</li>
</ul></div>
</li>
</ul></div>
<div class="paragraph"><p>And the others listed below are not.</p></div>
<div class="ulist"><ul>
<li>
<p>
Integer Properties
</p>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> logcount n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bit-count n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> integer-length n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> log2-binary-factors n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> first-set-bit n
</p>
</li>
</ul></div>
</li>
<li>
<p>
Bit Within Word
</p>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> logbit? index n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> bit-set? index n
</p>
</li>
<li>
<p>
<strong>procedure:</strong> copy-bit index from bit
</p>
</li>
</ul></div>
</li>
<li>
<p>
Field of Bits
</p>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> bit-field n start end
</p>
</li>
<li>
<p>
<strong>procedure:</strong> copy-bit-field to from start end
</p>
</li>
<li>
<p>
<strong>procedure:</strong> ash n count
</p>
</li>
<li>
<p>
<strong>procedure:</strong> arithmetic-shift n count
</p>
</li>
<li>
<p>
<strong>procedure:</strong> rotate-bit-field n count start end
</p>
</li>
<li>
<p>
<strong>procedure:</strong> reverse-bit-field n start end
</p>
</li>
</ul></div>
</li>
<li>
<p>
Bits as Booleans
</p>
<div class="ulist"><ul>
<li>
<p>
<strong>procedure:</strong> integer&#8594;list k len
</p>
</li>
<li>
<p>
<strong>procedure:</strong> integer&#8594;list k
</p>
</li>
<li>
<p>
<strong>procedure:</strong> list&#8594;integer list
</p>
</li>
<li>
<p>
<strong>procedure:</strong> booleans&#8594;integer bool1 &#8230;
</p>
</li>
</ul></div>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_srfi_69_basic_hash_tables">3.16. SRFI-69 Basic hash tables</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>It is just the reference implementation of SRFI-69. The hash functions are not
yet optimized for SigScheme.</p></div>
</div>
<div class="sect2">
<h3 id="_srfi_95_sorting_and_merging">3.17. SRFI-95 Sorting and Merging</h3>
<div class="paragraph"><p>Fully supported.</p></div>
<div class="paragraph"><p>It is just the reference implementation of SRFI-95 (sort.scm of SLIB).</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_r6rs_conformance">4. R6RS conformance</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_r6rs_characters">4.1. R6RS characters</h3>
<div class="paragraph"><p>R6RS characters are partially implemented based on R5.92RS. But since R6RS
specification is not finalized yet, future SigScheme may change the
specification around R6RS characters.</p></div>
<div class="sect3">
<h4 id="_current_r6rs_characters_status">4.1.1. Current R6RS characters status</h4>
<div class="ulist"><ul>
<li>
<p>
Supports Unicode character literals such as #\λ
</p>
</li>
<li>
<p>
Supports #x&lt;digit16&gt;+ literals
</p>
</li>
<li>
<p>
Supports \x&lt;digit16&gt;+; literals in string
</p>
</li>
<li>
<p>
Supports Unicode identifiers (but lacks character category validation)
</p>
</li>
<li>
<p>
Supports all named chars such as #\backspace, #\esc, and #\nul
</p>
</li>
<li>
<p>
Quoted-symbol by vertical bar (such as '|-symbol|) is not supported yet
</p>
</li>
<li>
<p>
Invalidly accepts non-all-lower-case character names such as #\Tab and #TAB
</p>
</li>
</ul></div>
</div>
<div class="sect3">
<h4 id="_todos">4.1.2. TODOs</h4>
<div class="ulist"><ul>
<li>
<p>
Support new escapes in string (\&lt;linefeed&gt; and \&lt;space&gt;)
</p>
</li>
<li>
<p>
Confirm symbol escape syntax (not defined in R6RS yet)
</p>
</li>
<li>
<p>
Support Unicode character category validation for identifiers
</p>
</li>
<li>
<p>
Disable #\newline on R6RS-compatible mode
</p>
</li>
</ul></div>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_sigscheme_extensions">5. SigScheme extensions</h2>
<div class="sectionbody">
<div class="paragraph"><p>If <code>--enable-sscm-extensions</code> is specified for configure script explicitly or
implicitly, these features can be used.</p></div>
<div class="sect2">
<h3 id="_legacy_macro">5.1. Legacy macro</h3>
<div class="paragraph"><p>Legacy and common <code>define-macro</code> is provided to define syntactic closures. But
SigScheme&#8217;s implementation is having some limitations.</p></div>
<div class="ulist"><ul>
<li>
<p>
The closure can only be defined with top-level environment due to an
    internal implementation trick
</p>
</li>
<li>
<p>
Macro forms are kept untransformed in program, and expanded immediately
    before each evaluation, as if they are ordinary syntaxes
</p>
</li>
<li>
<p>
<code>define-macro</code> destructively modifies closure object
</p>
</li>
</ul></div>
<div class="paragraph"><p>To avoid problems related to these limitations, side-effect in macros are
strongly discouraged. See following examples for each limitation.</p></div>
<div class="listingblock">
<div class="title">The closure can only be defined with top-level environment</div>
<div class="content">
<pre><code>(define-macro m
  (let ((?var 3))
    (lambda ()
      ?var)))    ==&gt;  error</code></pre>
</div></div>
<div class="listingblock">
<div class="title">Macro forms are kept untransformed in program</div>
<div class="content">
<pre><code>(define cnt 0)
(define-macro m
  (lambda ()
    (set! cnt (+ cnt 1))
    cnt))
(define proc-m
  (lambda ()
    (m)))

(proc-m)  ==&gt;  1
(proc-m)  ==&gt;  2  ;; ordinary Scheme implementation returns 1
(proc-m)  ==&gt;  3  ;; ordinary Scheme implementation returns 1</code></pre>
</div></div>
<div class="listingblock">
<div class="title"><code>define-macro</code> destructively modifies closure object</div>
<div class="content">
<pre><code>(define f
  (lambda (x) (* x x)))
(f (+ 1 2))     ==&gt;  9
(procedure? f)  ==&gt;  #t

(define-macro mf f)
(mf (+ 1 2))    ==&gt;  error
(mf 3)          ==&gt;  9
(f (+ 1 2))     ==&gt;  error
(procedure? f)  ==&gt;  error</code></pre>
</div></div>
<div class="paragraph"><p>See <code>test-legacy-macro.scm</code> to know more detailed specification.</p></div>
</div>
<div class="sect2">
<h3 id="_let_optionals">5.2. let-optionals*</h3>
<div class="paragraph"><p><code>let-optionals*</code> is provided for optional argument processing. The
specification is exactly same as Gauche 0.8.8. See <code>test-sscm-ext.scm</code> for
further information.</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_siod_compatibility">6. SIOD compatibility</h2>
<div class="sectionbody">
<div class="sect2">
<h3 id="_siod_specific_features">6.1. SIOD specific features</h3>
<div class="paragraph"><p>If <code>--enable-compat-siod</code> is specified for configure script explicitly or
implicitly, some SIOD compatible features are provided.</p></div>
<div class="ulist"><ul>
<li>
<p>
symbol-value
</p>
</li>
<li>
<p>
set-symbol-value!
</p>
</li>
<li>
<p>
verbose
</p>
</li>
<li>
<p>
undefine
</p>
</li>
<li>
<p>
eof-val
</p>
</li>
<li>
<p>
%%closure-code
</p>
</li>
<li>
<p>
bit-and
</p>
</li>
<li>
<p>
bit-or
</p>
</li>
<li>
<p>
bit-xor
</p>
</li>
<li>
<p>
bit-not
</p>
</li>
</ul></div>
</div>
<div class="sect2">
<h3 id="_siod_specific_behaviors">6.2. SIOD specific behaviors</h3>
<div class="paragraph"><p>If <code>--enable-compat-siod-bugs</code> is specified for configure script explicitly or
implicitly, some procedures and syntaxes emulate SIOD&#8217;s behavior. We call them
<em>bugs</em> for convention although they are not actually bugs on non-R5RS-compliant
SIOD implementation.</p></div>
<div class="ulist"><ul>
<li>
<p>
<code>#f</code> is identical to null list
</p>
</li>
<li>
<p>
<code>(car \'())</code> evaluates to <code>()</code>
</p>
</li>
<li>
<p>
<code>(cdr \'())</code> evaluates to <code>()</code>
</p>
</li>
<li>
<p>
<code>(if #f #t)</code> evaluates to <code>#f</code>
</p>
</li>
<li>
<p>
<code>let</code> and <code>let*</code> accepts value-less binding forms
</p>
</li>
<li>
<p>
<code>=</code> predicate can be applied to non-number objects
</p>
</li>
</ul></div>
<div class="listingblock">
<div class="title">#f is identical to null list</div>
<div class="content">
<pre><code>(null?    #f)   ==&gt;  #t
(null?    '())  ==&gt;  #t
(boolean? #f)   ==&gt;  #t
(boolean? '())  ==&gt;  #t
(if '() 'true 'false)  ==&gt;  false</code></pre>
</div></div>
<div class="listingblock">
<div class="title"><code>let</code> and <code>let*</code> accepts value-less binding forms</div>
<div class="content">
<pre><code>(let ((var))
  var)           ==&gt;  #f

(let* ((var))
  var)           ==&gt;  #f

(letrec ((var))
  var)           ==&gt;  error</code></pre>
</div></div>
<div class="listingblock">
<div class="title"><code>=</code> predicate can be applied to non-number objects</div>
<div class="content">
<pre><code>(require-extension (siod))

(= 3 (+ 1 2))         ==&gt;  #t
(= 3 (+ 1 2) 3)       ==&gt;  error  ;; only accepts 2 args

(define lst '(0 1 2))
(= lst lst)           ==&gt;  #t
(= lst (list 0 1 2))  ==&gt;  #f

;; '=' is defined as follows if --enable-compat-siod-bugs
(define =
  (let ((%= =))
    (lambda (x y)
      (or (eq? x y)
          (%= x y)))))</code></pre>
</div></div>
</div>
</div>
</div>
</div>
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