MzScheme returns the unique void value -- printed as
#<void> -- for expressions that have unspecified results in
R5RS. The procedure void takes any
number of arguments and returns void:

(voidv···) returns void.

(void?v) returns #t if v is void,
#f otherwise.

Variables bound by letrec-values that are accessible but
not yet initialized are bound to the unique undefined
value, printed as #<undefined>.

Unless otherwise specified, two instances of a particular MzScheme
data type are equal? only when they are eq?. Two
values are eqv? only when they are either eq?,
= and have the same exactness, or both +nan.0.

The andmap and ormap procedures apply a test
procedure to the elements of a list, returning immediately when the
result for testing the entire list is determined. The arguments to
andmap and ormap are the same as for map, but a
single boolean value is returned as the result, rather than a list:

(andmapproc list···^{1}) applies proc to elements of the
lists from the first elements to the last, returning #f
as soon as any application returns #f. If no application of
proc returns #f, then the result of the last application
of proc is returned. If the lists are empty, then
#t is returned.

(ormapproc list···^{1}) applies proc to elements of the
lists from the first elements to the last. If any application
returns a value other than #f, that value is immediately
returned as the result of the ormap application. If all
applications of proc return #f, then the result is
#f. If the lists are empty, then #f is returned.

a fixnum exact integer (30 bits^{2} plus a
sign bit)

a bignum exact integer (cannot be represented in a fixnum)

a fraction exact rational (represented by two exact integers)

a flonum inexact rational (double-precision floating-point number)

a complex number; either the real and imaginary
parts are both exact or inexact, or the number has an exact zero real
part and an inexact imaginary part; a complex number with an inexact
zero imaginary part is a real number

MzScheme extends the number syntax of R5RS in two ways:

All input
radixes (#b, #o, #d, and #x) allow
``decimal'' numbers that contain a period or exponent marker. For
example, #b1.1 is equivalent to 1.5. In hexadecimal
numbers, e always stands for a hexadecimal digit, not an
exponent marker.

The following are inexact
numerical constants: +inf.0 (infinity), -inf.0
(negative infinity), +nan.0 (not a number), and
-nan.0 (same as +nan.0). These names can also be
used within complex constants, as in -inf.0+inf.0i.

The special inexact numbers +inf.0, -inf.0, and
+nan.0 have no exact form. Dividing by an inexact zero returns
+inf.0 or -inf.0, depending on the sign of the
dividend. The infinities are integers, and they answer #t for
both even? and odd?. The +nan.0 value is not an
integer and is not = to itself, but +nan.0 is
eqv? to itself.^{3} Similarly, (=0.0-0.0)
is #t, but (eqv?0.0-0.0) is #f.

All multi-argument arithmetic procedures operate pairwise on arguments
from left to right.

The string->number procedure works on all number
representations and exact integer radix values in the range 2
to 16 (inclusive). The number->string procedure
accepts all number types and the radix values 2, 8,
10, and 16; however, if an inexact number is provided
with a radix other than 10, the
exn:application:mismatch exception is raised.

The add1 and sub1 procedures work on any number:

(add1z) returns z + 1.

(sub1z) returns z- 1.

The following procedures work on exact integers in their (semi-infinite) two's
complement representation:

(bitwise-iorn···^{1}) returns the bitwise ``inclusive or'' of
the ns.

(bitwise-andn···^{1}) returns the bitwise ``and'' of the
ns.

(bitwise-xorn···^{1}) returns the bitwise ``exclusive or'' of
the ns.

(bitwise-notn) returns the bitwise ``not'' of n.

(arithmetic-shiftn m) returns the bitwise ``shift'' of
n. The integer n is shifted left by m bits; i.e.,
m new zeros are introduced as rightmost digits. If m is
negative, n is shifted right by -m bits; i.e., the
rightmost m digits are dropped.

The random procedure generates pseudo-random integers:

(randomk) returns a random exact integer in the range
0 to k- 1 where k is an exact integer between 1
and 2^{31}- 1, inclusive. The number is provided by the current
pseudo-random number generator, which maintains an internal state for
generating numbers.^{4}

(random-seedk) seeds the current pseudo-random number
generator with k, an exact integer between 0 and 2^{31}- 1,
inclusive. Seeding a generator sets its internal state
deterministically; seeding a generator with a particular number
forces it to produce a sequence of pseudo-random numbers that is the
same across runs and across platforms.

(current-pseudo-random-generator) returns the current
pseudo-random number generator, and
(current-pseudo-random-generatorgenerator) sets the current
generator to generator. See also
section 7.4.1.10.

(make-pseudo-random-generator) returns a new pseudo-random
number generator. The new generator is seeded with a number derived
from (current-milliseconds).

(pseudo-random-generator?v) returns #t if v
is a pseudo-random number generator, #f otherwise.

The following procedures convert between Scheme numbers and common
machine byte representations:

(integer-byte-string->integerstring signed?[big-endian?])
converts the machine-format number encoded in string to
an exact integer. The string must contain either 2, 4, or 8
characters. If signed? is true, then the string is decoded as
a two's-complement number, otherwise it is decoded as an unsigned
integer. If big-endian? is true, then the first character's
ASCII value provides the most siginficant eight bits of the number,
otherwise the first character provides the least-significant eight
bits, and so on. The default value of big-endian? is the
result of system-big-endian?.

(integer->integer-byte-stringn size-n signed?[big-endian? to-string])
converts the exact integer n to a machine-format number encoded
in a string of length size-n, which must be 2, 4, or 8. If
signed? is true, then the number is encoded with two's
complement, otherwise it is encoded as an unsigned bit stream. If
big-endian? is true, then the most significant eight bits of
the number are encoded in the first character of the resulting
string, otherwise the least-significant bits are encoded in the first
character, and so on. The default value of big-endian? is the
result of system-big-endian?.

If to-string is provided, it must be a mutable string of length
size-n; in that case, the encoding of n is written into
to-string, and to-string is returned as the result. If
to-string is not provided, the result is a newly allocated
string.

If n cannot be encoded in a string of the requested size and
format, the exn:misc:application exception is raised. If to-string is
provided and it is not of length size-n, the
exn:misc:application exception is raised.

(floating-point-byte-string->realstring[big-endian?])
converts the IEEE floating-point number encoded in string
to an inexact real number. The string must contain
either 4 or 8 characters. If big-endian? is true, then the
first character's ASCII value provides the most siginficant eight
bits of the IEEE representation, otherwise the first character
provides the least-significant eight bits, and so on. The default
value of big-endian? is the result of
system-big-endian?.

(real->floating-point-byte-stringx size-n[big-endian? to-string])
converts the real number x to its IEEE representation in a
string of length size-n, which must be 4 or 8. If
big-endian? is true, then the most significant eight bits of
the number are encoded in the first character of the resulting
string, otherwise the least-significant bits are encoded in the first
character, and so on. The default value of big-endian? is the
result of system-big-endian?.

If to-string is provided, it must be a mutable string of length
size-n; in that case, the encoding of n is written into
to-string, and to-string is returned as the result. If
to-string is not provided, the result is a newly allocated
string.

If to-string is provided and it is not of length size-n,
the exn:misc:application exception is raised.

(system-big-endian?) returns #t if the native
encoding of numbers is big-endian for the machine running MzScheme,
#f if the native encoding is little-endian.

MzScheme character values range over the characters for ``extended
ASCII'' values 0 to 255 (where the ASCII extensions are
platform-specific). The procedure char->integer returns
the extended ASCII value of a character and integer->char
takes an extended ASCII value and returns the corresponding
character. If integer->char is given an integer that is
not in 0 to 255 inclusive, the exn:application:type exception is raised.

The procedures char->latin-1-integer and
latin-1-integer->char support conversions between characters in
the platform-specific character set and platform-independent Latin-1
(ISO 8859-1) values:

(char->latin-1-integerchar) returns the integer in 0 to
255 inclusive corresponding to the Latin-1 value for char, or
#f if char (in the platform-specific character set) has
no corresponding character in Latin-1.

(latin-1-integer->chark) returns the character
corresponding to the Latin-1 mapping of k, or #f if the
platform-specific character set does not support the corresponding
Latin-1 character. If k is not in 0 to 255 inclusive, the
exn:application:type exception is raised.

For Unix and Mac OS, char->latin-1-integer and
latin-1-integer->char are the same as char->integer
and integer->char. For Windows, the platform-specific set
and Latin-1 match except for the range #x80 to #x9F
(which are unprintable control characters in Latin-1).

The character comparison procedures -- char=?,
char<?, char-ci=?, etc. -- take two or more
character arguments and check the arguments pairwise (like the
numerical comparison procedures). Two characters are eq?
whenever they are char=?. The expression (char<?char1char2) produces the same result as (< (char->integerchar1)
(char->integerchar2)), etc. The procedures
char-whitespace?, char-alphabetic?,
char-numeric?, char-upper-case?, and
char-upper-case?, char-upcase, and
char-downcase are fully portable; their results do not
depend on the platform or locales.

In addition to the standard character procedures, MzScheme provides
the following locale-sensitive procedures (see
section 7.4.1.11):

(char-locale<?char1 char2···^{1})

(char-locale>?char1 char2···^{1})

(char-locale-ci=?char1 char2···^{1})

(char-locale-ci<?char1 char2···^{1})

(char-locale-ci>?char1 char2···^{1})

(char-locale-whitespace?char)

(char-locale-alphabetic?char)

(char-locale-numeric?char)

(char-locale-upper-case?char)

(char-locale-lower-case?char)

(char-locale-upcasechar)

(char-locale-downcasechar)

For example, since ASCII character 112 is a lowercase ``p'' and
Latin-1 character 246 is a lowercase ``ddoto'' (with an umlaut),
(char-locale<? (integer->char112) (integer->char246))
tends to produce #f, though it always produces #t
if the current locale is disabled.

A string can be mutable or immutable. When an immutable string is
provided to a procedure like string-set!, the
exn:application:type exception is raised.

String constants generated by read are
immutable. (string->immutable-stringstring) returns an immutable
string with the same content as string, returning string
if it is already an immutable string. (See also immutable?
in section 3.8.)

When a string is created with make-string without a fill value,
it is initialized with the null character (#\nul) in all
positions.

The string comparison procedures -- string=?,
string<?, string-ci=?, etc. -- take two or more
string arguments and check the arguments pairwise (like the numerical
comparison procedures). String comparisons using the standard
functions are fully portable; the results do not depend on the
platform or locales.

In addition to the string character procedures, MzScheme provides
the following locale-sensitive procedures (see
section 7.4.1.11):

For information about symbol parsing and printing, see
section 14.3 and section 14.4, respectively.

MzScheme provides two ways of generating an uninterned
symbol, i.e., a symbol that is not eq?, eqv?, or
equal? to any other symbol, although it may print the same
as another symbol:

(string->uninterned-symbolstring) is like
(string->symbolstring), but the resulting
symbol is a new uninterned symbol. Calling
string->uninterned-symbol twice with the same string
returns two distinct symbols.

(gensym[symbol/string]) creates an uninterned symbol with
an automatically-generated name. The optional symbol/string
argument is a prefix symbol or string.

Regular (interned) symbols are only weakly held by the internal symbol
table. This weakness can never affect the result of a eq?,
eqv?, or equal? test, but a symbol placed into a weak box
(see section 13.1) or used as the key in a weak hash table (see
section 3.12) may disappear.

When a vector is created with make-vector without a fill
value, it is initialized with 0 in all positions. A vector
can be immutable, such as a vector returned by syntax-e, but
vectors generated by read are mutable. (See also
immutable? in section 3.8.)

A cons cell can be mutable or immutable. When an immutable cons cell
is provided to a procedure like set-cdr!, the
exn:application:type exception is raised. Cons cells generated by read are always mutable.

The global variable null is bound to the empty list.

(reverse!list) is the same as (reverse list), but
list is destructively reversed using set-cdr!.

(append!list···^{1}) destructively appends the lists.

(list*v···^{1}) is similar to (listv···^{1})
but the last argument is used directly as the cdr of the last
pair constructed for the list:

(list*1234) ; => '(123 . 4)

(cons-immutablev1 v2) returns an immutable pair whose
car is v1 and cdr is v2.

(list-immutablev···^{1}) is like (listv···^{1}), but using
immutable pairs.

(list*-immutablev···^{1}) is like (list*v···^{1}), but using
immutable pairs.

(immutable?v) returns #t if v is an immutable
cons cell, string, vector, or box, #f otherwise.

The list-ref and list-tail procedures accept an
improper list as a first argument. If either procedure is applied to
an improper list and an index that would require taking the car
or cdr of a non-cons-cell, the
exn:application:mismatch exception is raised.

The member, memv, and memq procedures
accept an improper list as a second argument. If the membership
search reaches the improper tail, the
exn:application:mismatch exception is raised.

The assoc, assv, and assq procedures
accept an improperly formed association list as a second argument.
If the association search reaches an improper list tail or a list
element that is not a pair, the exn:application:mismatch exception is raised.

MzScheme provides boxes, records with a single mutable
field:

(boxv) returns a new box that contains v.

(unboxbox) returns the content of box. For any
v, (unbox (box v)) returns v.

(set-box!box v) sets the content of box to
v.

(box?v) returns #t if v is a box, #f
otherwise.

Two boxes are equal? if the contents of the boxes are
equal?.

A box returned by syntax-e (see section 12.2.2) is
immutable; if set-box! is applied to such a box, the
exn:application:type exception is raised. A box produced by read (via
#&) is mutable. (See also immutable? in
section 3.8.)

When compiling a lambda or case-lambda expression,
MzScheme looks for a 'method-arity-error property
attached to the expression (see section 12.6.2). If it is present
with a true value, and if no case of the procedure accepts zero
arguments, then the procedure is marked so that an
exn:application:arity exception involving the procedure
will hide the first argument, if one was provided. (Hiding the first
argument is useful when the procedure implements a method, where the
first argument is implicit in the original source). The property
affects only the format of exn:application:arity exceptions,
not the result of procedure-arity.

A primitive procedure is a built-in procedure that is
implemented in low-level language. Not all built-in procedures are
primitives, but almost all R5RS procedures are primitives, as
are most of the procedures described in this manual.

(primitive?v) returns #t if v is a primitive
procedure or #f otherwise.

(primitive-result-arityprim-proc) returns the arity of the
result of the primitive procedure prim-proc (as opposed to the
procedure's input arity as returned by arity; see
section 3.10.1). For most primitives, this procedure returns 1,
since most primitives return a single value when applied. For
information about arity values, see section 3.10.1.

(primitive-closure?v) returns #t if v is
internally implemented as a primitive closure rather than an simple
primitive procedure, #f otherwise. This information is
intended for use by the mzc compiler.

(make-hash-table[flag-symbol flag-symbol]) creates and
returns a new hash table. If provided, each flag-symbol must
one of the following:

'weak -- creates a hash table with weakly-held
keys (see section 13.1).

'equal -- creates a hash table that compares
keys using equal? instead of eq? (needed, for
example, when using strings as keys).

By default, key comparisons use eq?. If the second
flag-symbol is redundant, the
exn:application:mismatch exception is raised.

(hash-table?v) returns #t if v was created by
make-hash-table, #f otherwise.

(hash-table-put!hash-table key-v v) maps key-v to
v in hash-table, overwriting any existing mapping for
key-v.

(hash-table-gethash-table key-v[failure-thunk]) returns the
value for key-v in hash-table. If no value is found for
key-v, then the result of invoking failure-thunk (a
procedure of no arguments) is returned. If failure-thunk is not
provided, the exn:application:mismatch exception is raised when no value is
found for key-v.

(hash-table-remove!hash-table key-v) removes the value
mapping for key-v if it exists in hash-table.

(hash-table-maphash-table proc) applies the procedure proc
to each element in hash-table, accumulating the results into a
list. The procedure proc must take two arguments: a key and its
value. See the caveat below about concurrent access.

(hash-table-for-eachhash-table proc) applies the procedure
proc to each element in hash-table (for the side-effects
of proc) and returns void. The procedure proc must
take two arguments: a key and its value. See the caveat below about
concurrent access.

(eq-hash-codev) returns a number; for any two eq?
values, the returned number is always the same. The number is an
exact integer that is itself guaranteed to be eq? with any
value representing the same exact integer (i.e., it is a fixnum).

(equal-hash-codev) returns a number; for any two equal?
values, the returned number is always the same. The number is an
exact integer that is itself guaranteed to be eq? with any
value representing the same exact integer (i.e., it is a fixnum). If
v contains a cycle consisting of pairs, vectors, boxes, and
fully-inspectable structures, then equal-hash-code applied
to v will loop indefinitely.

Caveat concerning concurrent access: A hash table can be
manipulated with hash-table-get, hash-table-put!,
and hash-table-remove! concurrently by multiple threads,
and the operations are protected by a table-specific semaphore as
needed. A few caveats apply, however:

If a thread is terminated while applying
hash-table-get, hash-table-put!, or
hash-table-remove! to a hash table that uses equal?
comparisons, all current and future operations on the hash table
block indefinitely.

The hash-table-map and hash-table-for-each
procedures do not use the table's semaphore. Consequently, if a hash
table is modified by another thread while a map for for-each is in
process, arbitrary key-value pairs can be dropped or duplicated in
the map or for-each.

Caveat concerning mutable keys: If a key into an
equal?-based hash table is mutated (e.g., a key string is
modified with string-set!), then the hash table's behavior
put and get operations become unpredictable.

^{2} 30 bits for
a 32-bit architecture, 62 bits for a 64-bit architecture.

^{3} This definition of eqv?
technically contradicts R5RS, but R5RS does not address
strange ``numbers'' like +nan.0.

^{4} The random number generator uses a
relatively standard Unix random() implementation in its
degree-seven polynomial mode.

^{5} All fields of the
arity-at-least structure type are accessible by all
inspectors (see section 4.6).