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Unit library

This unit contains basic Scheme definitions. This unit is used by default, unless the program is compiled with the -explicit-use option.

Arithmetic

[procedure] (sub1 N)

Binary integer operations

Binary integer operations. arithmetic-shift shifts the argument N1 by N2 bits to the left. If N2 is negative, than N1 is shifted to the right. These operations only accept exact integers or inexact integers in word range (32 bit signed on 32-bit platforms, or 64 bit signed on 64-bit platforms).

[procedure] (bitwise-and N1 ...)
[procedure] (bitwise-ior N1 ...)
[procedure] (bitwise-xor N1 ...)
[procedure] (bitwise-not N)
[procedure] (arithmetic-shift N1 N2)

bit-set?

[procedure] (bit-set? N INDEX)

Returns #t if the bit at the position INDEX in the integer N is set, or #f otherwise. The rightmost/least-significant bit is bit 0.

Arithmetic fixnum operations

These procedures do not check their arguments, so non-fixnum parameters will result in incorrect results. fxneg negates its argument.

On division by zero, fx/ and fxmod signal a condition of kind (exn arithmetic).

fxshl and fxshr perform arithmetic shift left and right, respectively.

[procedure] (fx+ N1 N2)
[procedure] (fx- N1 N2)
[procedure] (fx* N1 N2)
[procedure] (fx/ N1 N2)
[procedure] (fxmod N1 N2)
[procedure] (fxneg N)
[procedure] (fxmin N1 N2)
[procedure] (fxmax N1 N2)
[procedure] (fx= N1 N2)
[procedure] (fx> N1 N2)
[procedure] (fx< N1 N2)
[procedure] (fx>= N1 N2)
[procedure] (fx<= N1 N2)
[procedure] (fxand N1 N2)
[procedure] (fxior N1 N2)
[procedure] (fxxor N1 N2)
[procedure] (fxnot N)
[procedure] (fxshl N1 N2)
[procedure] (fxshr N1 N2)

fixnum?

`[procedure] (fixnum? X)`

Returns #t if X is a fixnum, or #f otherwise.

Fixnum limits

most-positive-fixnum

most-negative-fixnum

fixnum-bits

fixnum-precision

Arithmetic floating-point operations

arguments (except flonum?, which returns #f). In unsafe mode, these procedures do not check their arguments. A non-flonum argument in unsafe mode can crash the system.

[procedure] (flonum? X)
[procedure] (fp+ X Y)
[procedure] (fp- X Y)
[procedure] (fp* X Y)
[procedure] (fp/ X Y)
[procedure] (fpneg X)
[procedure] (fpmin X Y)
[procedure] (fpmax X Y)
[procedure] (fp= X Y)
[procedure] (fp> X Y)
[procedure] (fp< X Y)
[procedure] (fp>= X Y)
[procedure] (fp<= X Y)

flonum?

`[procedure] (flonum? X)`

Returns #t if X is a flonum, or #f otherwise.

Flonum limits

maximum-flonum

minimum-flonum

flonum-epsilon

flonum-precision

flonum-decimal-precision

flonum-maximum-exponent

flonum-minimum-exponent

flonum-maximum-decimal-exponent

flonum-minimum-decimal-exponent

finite?

[procedure] (finite? N)

Returns #f if N is negative or positive infinity, and #t otherwise.

signum

`[procedure] (signum N)`

Returns 1 if N is positive, -1 if N is negative or 0 if N is zero. signum is exactness preserving.

File Input/Output

current-output-port

[procedure] (current-output-port [PORT])

Returns default output port. If PORT is given, then that port is selected as the new current output port.

Note that the default output port is not buffered. Use set-buffering-mode! if you need a different behavior.

current-error-port

[procedure] (current-error-port [PORT])

Returns default error output port. If PORT is given, then that port is selected as the new current error output port.

Note that the default error output port is not buffered. Use set-buffering-mode! if you need a different behavior.

flush-output

[procedure] (flush-output [PORT])

Write buffered output to the given output-port. PORT defaults to the value of (current-output-port).

port-name

[procedure] (port-name [PORT])

Fetch filename from PORT. This returns the filename that was used to open this file. Returns a special tag string, enclosed into parentheses for non-file ports. PORT defaults to the value of (current-input-port).

port-position

[procedure] (port-position [PORT])

Returns the current position of PORT as two values: row and column number. If the port does not support such an operation an error is signaled. This procedure is currently only available for input ports. PORT defaults to the value of (current-input-port).

set-port-name!

[procedure] (set-port-name! PORT STRING)

Sets the name of PORT to STRING.

Files

delete-file

[procedure] (delete-file STRING)

Deletes the file with the pathname STRING. If the file does not exist, an error is signaled.

directory-exists?

[procedure] (directory-exists? STRING)

Returns STRING if a directory with the given pathname exists, or #f otherwise.

file-exists?

[procedure] (file-exists? STRING)

Returns STRING if a file or directory with the given pathname exists, or #f otherwise.

rename-file

[procedure] (rename-file OLD NEW)

Renames the file or directory with the pathname OLD to NEW. If the operation does not succeed, an error is signaled.

String ports

get-output-string

[procedure] (get-output-string PORT)

Returns accumulated output of a port created with (open-output-string).

open-input-string

[procedure] (open-input-string STRING)

Returns a port for reading from STRING.

open-output-string

[procedure] (open-output-string)

Returns a port for accumulating output in a string.

Feature identifiers

CHICKEN maintains a global list of features naming functionality available in the current system. Additionally the cond-expand form accesses this feature list to infer what features are provided. Predefined features are chicken, and the SRFIs (Scheme Request For Implementation) provided by the base system: srfi-23, srfi-30, srfi-39. If the eval unit is used (the default), the features srfi-0, srfi-2, srfi-6, srfi-8, srfi-9 and srfi-10 are defined. When compiling code (during compile-time) the feature compiling is registered. When evaluating code in the interpreter (csi), the feature csi is registered.

features

[procedure] (features)

Returns a list of all registered features that will be accepted as valid feature-identifiers by cond-expand.

feature?

[procedure] (feature? ID ...)

Returns #t if all features with the given feature-identifiers ID ... are registered.

register-feature!

[procedure] (register-feature! FEATURE ...)

Register one or more features that will be accepted as valid feature-identifiers by cond-expand. FEATURE ... may be a keyword, string or symbol.

unregister-feature!

[procedure] (unregister-feature! FEATURE ...)

Unregisters the specified feature-identifiers. FEATURE ... may be a keyword, string or symbol.

Keywords

Keywords are special symbols prefixed with #: that evaluate to themselves. Procedures can use keywords to accept optional named parameters in addition to normal required parameters. Assignment to and bindings of keyword symbols is not allowed. The parameter keyword-style and the compiler/interpreter option -keyword-style can be used to allow an additional keyword syntax, either compatible to Common LISP, or to DSSSL.

get-keyword

[procedure] (get-keyword KEYWORD ARGLIST [THUNK])

Returns the argument from ARGLIST specified under the keyword KEYWORD. If the keyword is not found, then the zero-argument procedure THUNK is invoked and the result value is returned. If THUNK is not given, #f is returned.

```(define (increase x . args)
(+ x (get-keyword #:amount args (lambda () 1))) )
(increase 123)                                      ==> 124
(increase 123 #:amount 10)                          ==> 133```

Note: the KEYWORD may actually be any kind of object.

keyword?

[procedure] (keyword? X)

Returns #t if X is a keyword symbol, or #f otherwise.

keyword->string

[procedure] (keyword->string KEYWORD)

Transforms KEYWORD into a string.

string->keyword

[procedure] (string->keyword STRING)

Returns a keyword with the name STRING.

Exceptions

CHICKEN implements the (currently withdrawn) SRFI-12 exception system. For more information, see the SRFI-12 document.

condition-case

`[syntax] (condition-case EXPRESSION CLAUSE ...)`

Evaluates EXPRESSION and handles any exceptions that are covered by CLAUSE ..., where CLAUSE should be of the following form:

`CLAUSE = ([VARIABLE] (KIND ...) BODY ...)`

If provided, VARIABLE will be bound to the signaled exception object. BODY ... is executed when the exception is a property- or composite condition with the kinds given KIND ... (unevaluated). If no clause applies, the exception is re-signaled in the same dynamic context as the condition-case form.

```(define (check thunk)
(condition-case (thunk)
[(exn file) (print "file error")]
[(exn) (print "other error")]
[var () (print "something else")] ) )

(check (lambda () (open-input-file "")))   ; -> "file error"
(check (lambda () some-unbound-variable))  ; -> "othererror"
(check (lambda () (signal 99)))            ; -> "something else"

(condition-case some-unbound-variable
[(exn file) (print "ignored")] )      ; -> signals error
```

breakpoint

[procedure] (breakpoint [NAME])

Programmatically triggers a breakpoint (similar to the ,br top-level csi command).

All error-conditions signaled by the system are of kind exn. The following composite conditions are additionally defined:

 (exn arity) Signaled when a procedure is called with the wrong number of arguments. (exn type) Signaled on type-mismatch errors, for example when an argument of the wrong type is passed to a built-in procedure. (exn arithmetic) Signaled on arithmetic errors, like division by zero. (exn i/o) Signaled on input/output errors. (exn i/o file) Signaled on file-related errors. (exn i/o net) Signaled on network errors. (exn bounds) Signaled on errors caused by accessing non-existent elements of a collection. (exn runtime) Signaled on low-level runtime-system error-situations. (exn runtime limit) Signaled when an internal limit is exceeded (like running out of memory). (exn match) Signaled on errors raised by failed matches (see the section on match). (exn syntax) Signaled on syntax errors. (exn breakpoint) Signaled when a breakpoint is reached.

Notes:

• All error-exceptions (of the kind exn) are non-continuable.
• Error-exceptions of the exn kind have additional arguments and location properties that contain the arguments passed to the exception-handler and the name of the procedure where the error occurred (if available).
• When the posix unit is available and used, then a user-interrupt (signal/int) signals an exception of the kind user-interrupt.
• the procedure condition-property-accessor accepts an optional third argument. If the condition does not have a value for the desired property and if the optional argument is given, no error is signaled and the accessor returns the third argument.
• In composite conditions all properties are currently collected in a single property-list, so in the case that to conditions have the same named property, only one will be visible.

Environment information and system interface

argv

[procedure] (argv)

Return a list of all supplied command-line arguments. The first item in the list is a string containing the name of the executing program. The other items are the arguments passed to the application. This list is freshly created on every invocation of (argv). It depends on the host-shell whether arguments are expanded ('globbed') or not.

exit

[procedure] (exit [CODE])

Exit the running process and return exit-code, which defaults to 0 (Invokes exit-handler).

Note that pending dynamic-wind thunks are not invoked when exiting your program in this way.

build-platform

[procedure] (build-platform)

Returns a symbol specifying the toolset which has been used for building the executing system, which is one of the following:

```cygwin
mingw32
gnu
intel
unknown```

chicken-version

[procedure] (chicken-version [FULL])

Returns a string containing the version number of the CHICKEN runtime system. If the optional argument FULL is given and true, then a full version string is returned.

errno

[procedure] (errno)

Returns the error code of the last system call.

get-environment-variable

```[procedure] (get-environment-variable STRING)
[procedure] (getenv STRING)```

Returns the value of the environment variable STRING or #f if that variable is not defined. See also SRFI-98. getenv is an alias for get-environment-variable.

machine-byte-order

[procedure] (machine-byte-order)

Returns the symbol little-endian or big-endian, depending on the machine's byte-order.

machine-type

[procedure] (machine-type)

Returns a symbol specifying the processor on which this process is currently running, which is one of the following:

```alpha
mips
hppa
ultrasparc
sparc
ppc
ppc64
ia64
x86
x86-64
unknown```

on-exit

[procedure] (on-exit THUNK)

Schedules the zero-argument procedures THUNK to be executed before the process exits, either explicitly via exit or implicitly after execution of the last top-level form. Note that finalizers for unreferenced finalized data are run before exit procedures.

software-type

[procedure] (software-type)

Returns a symbol specifying the operating system on which this process is currently running, which is one of the following:

```windows
unix
macos
ecos
unknown```

software-version

[procedure] (software-version)

Returns a symbol specifying the operating system version on which this process is currently running, which is one of the following:

```linux
freebsd
netbsd
openbsd
macosx
hpux
solaris
sunos
unknown```

c-runtime

[procedure] (c-runtime)

Returns a symbol that designates what kind of C runtime library has been linked with this version of the Chicken libraries. Possible return values are static, dynamic or unknown. On systems not compiled with the Microsoft C compiler, c-runtime always returns unknown.

system

[procedure] (system STRING)

Execute shell command. The functionality offered by this procedure depends on the capabilities of the host shell. If the forking of a subprocess failed, an exception is raised. Otherwise the return status of the subprocess is returned unaltered.

On a UNIX system, that value is the raw return value of waitpid(2), which contains signal, core dump and exit status. It is 0 on success. To pull out the signal number or exit status portably requires POSIX calls, but in a pinch you can use something like this:

```;; Returns two values: #t if the process exited normally or #f otherwise;
;; and either the exit status, or the signal number if terminated via signal.
(define (process-status rc)
(define (wait-signaled? x) (not (= 0 (bitwise-and x 127))))
(define (wait-signal x) (bitwise-and x 127))
(define (wait-exit-status x) (arithmetic-shift x -8))
(if (wait-signaled? rc)
(values #f (wait-signal rc))
(values #t (wait-exit-status rc))))```
```#;> (process-status (system "exit 42"))
#t
42```

Execution time

cpu-time

[procedure] (cpu-time)

Returns the used CPU time of the current process in milliseconds as two values: the time spent in user code, and the time spent in system code. On platforms where user and system time can not be differentiated, system time will be always be 0.

current-milliseconds

[procedure] (current-milliseconds)

Returns the number of milliseconds since process- or machine startup.

current-seconds

[procedure] (current-seconds)

Returns the number of seconds since midnight, Jan. 1, 1970.

current-gc-milliseconds

[procedure] (current-gc-milliseconds)

Returns the number of milliseconds spent in major garbage collections since the last call of current-gc-milliseconds and returns an exact integer.

Interrupts and error-handling

enable-warnings

[procedure] (enable-warnings [BOOL])

Enables or disables warnings, depending on wether BOOL is true or false. If called with no arguments, this procedure returns #t if warnings are currently enabled, or #f otherwise. Note that this is not a parameter. The current state (whether warnings are enabled or disabled) is global and not thread-local.

error

[procedure] (error [LOCATION] [STRING] EXP ...)

Prints error message, writes all extra arguments to the value of (current-error-port) and invokes the current exception-handler. This conforms to SRFI-23. If LOCATION is given and a symbol, it specifies the location (the name of the procedure) where the error occurred.

get-call-chain

Returns a list with the call history. Backtrace information is only generated in code compiled without -no-trace and evaluated code. If the optional argument START is given, the backtrace starts at this offset, i.e. when START is 1, the next to last trace-entry is printed, and so on. If the optional argument THREAD is given, then the call-chain will only be constructed for calls performed by this thread.

Prints a backtrace of the procedure call history to PORT, which defaults to (current-output-port).

[procedure] (print-error-message EXN [PORT [STRING]])

Prints an appropriate error message to PORT (which defaults to the value of (current-output-port) for the object EXN. EXN may be a condition, a string or any other object. If the optional argument STRING is given, it is printed before the error-message. STRING defaults to "Error:".

procedure-information

[procedure] (procedure-information PROC)

Returns an s-expression with debug information for the procedure PROC, or #f, if PROC has no associated debug information.

reset

[procedure] (reset)

Reset program (Invokes reset-handler).

warning

[procedure] (warning STRING EXP ...)

Displays a warning message (if warnings are enabled with enable-warnings) and continues execution.

singlestep

[procedure] (singlestep THUNK)

Executes the code in the zero-procedure THUNK in single-stepping mode.

Garbage collection

gc

[procedure] (gc [FLAG])

Invokes a garbage-collection and returns the number of free bytes in the heap. The flag specifies whether a minor (#f) or major (#t) GC is to be triggered. If no argument is given, #t is assumed. An explicit #t argument will cause all pending finalizers to be executed.

memory-statistics

[procedure] (memory-statistics)

Performs a major garbage collection and returns a three element vector containing the total heap size in bytes, the number of bytes currently used and the size of the nursery (the first heap generation). Note that the actual heap is actually twice the size given in the heap size, because CHICKEN uses a copying semi-space collector.

set-finalizer!

[procedure] (set-finalizer! X PROC)

Registers a procedure of one argument PROC, that will be called as soon as the non-immediate data object X is about to be garbage-collected (with that object as its argument). Note that the finalizer will not be called while interrupts are disabled. This procedure returns X.

Finalizers are invoked asynchronously, in the thread that happens to be currently running.

set-gc-report!

[procedure] (set-gc-report! FLAG)

Print statistics after every GC, depending on FLAG. A value of #t shows statistics after every major GC. A true value different from #t shows statistics after every minor GC. #f switches statistics off.

Other control structures

promise?

[procedure] (promise? X)

Returns #t if X is a promise returned by delay, or #f otherwise.

String utilities

reverse-list->string

[procedure] (reverse-list->string LIST)

Returns a string with the characters in LIST in reverse order. This is equivalent to (list->string (reverse LIST)), but much more efficient.

Generating uninterned symbols

gensym

[procedure] (gensym [STRING-OR-SYMBOL])

Returns a newly created uninterned symbol. If an argument is provided, the new symbol is prefixed with that argument.

string->uninterned-symbol

[procedure] (string->uninterned-symbol STRING)

Returns a newly created, unique symbol with the name STRING.

Standard Input/Output

port?

[procedure] (port? X)

Returns #t if X is a port object or #f otherwise.

print

[procedure] (print [EXP1 ...])

Outputs the optional arguments EXP1 ... using display and writes a newline character to the port that is the value of (current-output-port). Returns (void).

print*

[procedure] (print* [EXP1 ...])

Similar to print, but does not output a terminating newline character and performs a flush-output after writing its arguments.

User-defined named characters

char-name

[procedure] (char-name SYMBOL-OR-CHAR [CHAR])

This procedure can be used to inquire about character names or to define new ones. With a single argument the behavior is as follows: If SYMBOL-OR-CHAR is a symbol, then char-name returns the character with this name, or #f if no character is defined under this name. If SYMBOL-OR-CHAR is a character, then the name of the character is returned as a symbol, or #f if the character has no associated name.

If the optional argument CHAR is provided, then SYMBOL-OR-CHAR should be a symbol that will be the new name of the given character. If multiple names designate the same character, then the write will use the character name that was defined last.

```(char-name 'space)                  ==> #\space
(char-name #\space)                 ==> space
(char-name 'bell)                   ==> #f
(char-name (integer->char 7))       ==> #f
(char-name 'bell (integer->char 7))
(char-name 'bell)                   ==> #\bell
(char->integer (char-name 'bell))   ==> 7```

Blobs

"blobs" are collections of unstructured bytes. You can't do much with them, but allow conversion to and from SRFI-4 number vectors.

make-blob

[procedure] (make-blob SIZE)

Returns a blob object of SIZE bytes, aligned on an 8-byte boundary, uninitialized.

blob?

[procedure] (blob? X)

Returns #t if X is a blob object, or #f otherwise.

blob-size

[procedure] (blob-size BLOB)

Returns the number of bytes in BLOB.

blob->string

[procedure] (blob->string BLOB)

Returns a string with the contents of BLOB.

string->blob

[procedure] (string->blob STRING)

Returns a blob with the contents of STRING.

blob=?

[procedure] (blob=? BLOB1 BLOB2)

Returns #t if the two argument blobs are of the same size and have the same content.

Vectors

vector-copy!

[procedure] (vector-copy! VECTOR1 VECTOR2 [COUNT])

Copies contents of VECTOR1 into VECTOR2. If the argument COUNT is given, it specifies the maximal number of elements to be copied. If not given, the minimum of the lengths of the argument vectors is copied.

Exceptions: (exn bounds)

vector-resize

[procedure] (vector-resize VECTOR N [INIT])

Creates and returns a new vector with the contents of VECTOR and length N. If N is greater than the original length of VECTOR, then all additional items are initialized to INIT. If INIT is not specified, the contents are initialized to some unspecified value.

The unspecified value

void

[procedure] (void)

Returns an unspecified value.

Continuations

call/cc

[procedure] (call/cc PROCEDURE)

An alias for call-with-current-continuation.

continuation-capture

[procedure] (continuation-capture PROCEDURE)

Creates a continuation object representing the current continuation and tail-calls PROCEDURE with this continuation as the single argument.

continuation?

[procedure] (continuation? X)

Returns #t if X is a continuation object, or #f otherwise. Please note that this applies only to continuations created by the Continuation API, but not by call/cc, i.e.: (call-with-current-continuation continuation?) returns #f, whereas (continuation-capture continuation?) returns #t.

continuation-graft

[procedure] (continuation-graft CONT THUNK)

Calls the procedure THUNK with no arguments and the implicit continuation CONT.

continuation-return

[procedure] (continuation-return CONT VALUE ...)

Returns the value(s) to the continuation CONT. continuation-return could be implemented like this:

```(define (continuation-return k . vals)
(continuation-graft
k
(lambda () (apply values vals)) ) )```

Setters

setter

[procedure] (setter PROCEDURE)

Returns the setter-procedure of PROCEDURE, or signals an error if PROCEDURE has no associated setter-procedure.

Note that (set! (setter PROC) ...) for a procedure that has no associated setter procedure yet is a very slow operation (the old procedure is replaced by a modified copy, which involves a garbage collection).

getter-with-setter

[procedure] (getter-with-setter GETTER SETTER)

Returns a copy of the procedure GETTER with the associated setter procedure SETTER. Contrary to the SRFI specification, the setter of the returned procedure may be changed.

Define new read-time constructor for #, read syntax. For further information, see the documentation for SRFI-10.

When the reader encounters the non-whitespace character CHAR while reading an expression from a given port, then the procedure PROC will be called with that port as its argument. The procedure should return a value that will be returned to the reader:

``` ; A simple RGB color syntax:

(lambda (port)
(apply vector
(map (cut string->number <> 16)
(string-chop (read-string 6 port) 2) ) ) ) )

(with-input-from-string "(1 2 %f0f0f0 3)" read)
; ==> (1 2 #(240 240 240) 3)```

If CHAR-OR-SYMBOL is a symbol, then a so-called read-mark handler is defined. In that case the handler procedure will be called when a character-sequence of the form

`#!SYMBOL`

is encountered.

You can undo special handling of read-syntax by passing #f as the second argument (if the syntax was previously defined via set-read-syntax!).

Note that all of CHICKEN's special non-standard read-syntax is handled directly by the reader. To disable built-in read-syntax, define a handler that triggers an error (for example).

Similar to set-read-syntax!, but allows defining new #<CHAR> ... reader syntax. If the first argument is a symbol, then this procedure is equivalent to set-read-syntax!.

Similar to set-sharp-read-syntax!, but intended for defining reader syntax of the form #<NUMBER><CHAR> .... The handler procedure PROC will be called with two arguments: the input port and the number preceding the dispatching character. If the first argument is a symbol, then this procedure is equivalent to set-read-syntax!.

Property lists

As in other Lisp dialects, CHICKEN supports "property lists" associated with symbols. Properties are accessible via a key that can be any kind of value but which will be compared using eq?.

get

` [procedure] (get SYMBOL PROPERTY [DEFAULT])`

Returns the value stored under the key PROPERTY in the property list of SYMBOL. If no such property is stored, returns DEFAULT. The DEFAULT is optional and defaults to #f.

put!

``` [procedure] (put! SYMBOL PROPERTY VALUE)
[setter] (set! (get SYMBOL PROPERTY) VALUE)```

Stores VALUE under the key PROPERTY in the property list of SYMBOL replacing any previously stored value.

remprop!

` [procedure] (remprop! SYMBOL PROPERTY)`

Deletes the first property matching the key PROPERTY in the property list of SYMBOL. Returns #t when a deletion performed, and #f otherwise.

symbol-plist

``` [procedure] (symbol-plist SYMBOL)
[setter] (set! (symbol-plist SYMBOL) LST)```

Returns the property list of SYMBOL or sets it.

get-properties

` [procedure] (get-properties SYMBOL PROPERTIES)`

Searches the property list of SYMBOL for the first property with a key in the list PROPERTIES. Returns 3 values: the matching property key, value, and the tail of property list after the matching property. When no match found all values are #f.

PROPERTIES may also be an atom, in which case it is treated as a list of one element.

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