~ chicken-core (master) /manual/Module (chicken base)
Trap1[[tags: manual]]2[[toc:]]34== Module (chicken base)56Core procedures and macros, acting as basic extensions to the R7RS7standard and other essential features.89This module is used by default, unless a program is compiled with10the {{-explicit-use}} option.1112=== Numeric predicates1314These allow you to make a more precise differentiation between number15types and their properties, not provided by R7RS.1617==== fixnum?1819<procedure>(fixnum? X)</procedure>2021Returns {{#t}} if {{X}} is a fixnum, or {{#f}} otherwise.2223==== flonum?2425<procedure>(flonum? X)</procedure>2627Returns {{#t}} if {{X}} is a flonum, or {{#f}} otherwise.2829==== bignum?3031<procedure>(bignum? X)</procedure>3233Returns {{#t}} if {{X}} is a bignum (integer larger than fits in a34fixnum), or {{#f}} otherwise.3536==== exact-integer?3738<procedure>(exact-integer? X)</procedure>3940Returns {{#t}} if {{X}} is an exact integer (i.e., a fixnum or a41bignum), or {{#f}} otherwise.4243This procedure is compatible with the definition from the R7RS44{{(scheme base)}} library.4546==== cplxnum?4748<procedure>(cplxnum? X)</procedure>4950Returns {{#t}} if {{X}} is a true complex number (it has an imaginary51component), or {{#f}} otherwise.5253Please note that {{complex?}} will always return {{#t}} for any number54type supported by CHICKEN, so you can use this predicate if you want55to know the representational type of a number.5657==== ratnum?5859<procedure>(ratnum? X)</procedure>6061Returns {{#t}} if {{X}} is a true rational number (it is a fraction62with a denominator that's not 1), or {{#f}} otherwise.6364Please note that {{rational?}} will always return {{#t}} for any65number type supported by CHICKEN except complex numbers and non-finite66flonums, so you can use this predicate if you want to know the67representational type of a number.6869==== nan?7071<procedure>(nan? N)</procedure>7273Returns {{#t}} if {{N}} is not a number (a IEEE flonum NaN-value). If74{{N}} is a complex number, it's considered nan if it has a real or75imaginary component that's nan.7677This procedure is compatible with the definition from the R7RS78{{(scheme inexact)}} library.7980==== infinite?8182<procedure>(infinite? N)</procedure>8384Returns {{#t}} if {{N}} is negative or positive infinity, and {{#f}}85otherwise. If {{N}} is a complex number, it's considered infinite if86it has a real or imaginary component that's infinite.8788This procedure is compatible with the definition from the R7RS89{{(scheme inexact)}} library.9091==== finite?9293<procedure>(finite? N)</procedure>9495Returns {{#t}} if {{N}} represents a finite number and {{#f}}96otherwise. Positive and negative infinity as well as NaNs are not97considered finite. If {{N}} is a complex number, it's considered98finite if both the real and imaginary components are finite.99100This procedure is compatible with the definition from the R7RS101{{(scheme inexact)}} library.102103==== equal=?104105<procedure>(equal=? X y)</procedure>106107Similar to the standard procedure {{equal?}}, but compares numbers108using the {{=}} operator, so {{equal=?}} allows structural comparison109in combination with comparison of numerical data by value.110111112=== Arithmetic113114==== add1/sub1115116<procedure>(add1 N)</procedure>117<procedure>(sub1 N)</procedure>118119Adds/subtracts 1 from {{N}}.120121122==== exact-integer-nth-root123124<procedure>(exact-integer-nth-root K N)</procedure>125126Like {{exact-integer-sqrt}}, but with any base value. Calculates127{{\sqrt[N]{K}}}, the {{N}}th root of {{K}} and returns two values128{{s}} and {{r}} where {{s^N + r = K}} and {{K < (s+1)^N}}.129130131==== Division with quotient and remainder132133<procedure>(quotient&remainder X Y)</procedure>134<procedure>(quotient&modulo X Y)</procedure>135136Returns two values: the quotient and the remainder (or modulo) of137{{X}} divided by {{Y}}. Could be defined as {{(values (quotient X Y)138(remainder X Y))}}, but is much more efficient when dividing very139large numbers.140141==== signum142143<procedure>(signum N)</procedure>144145For real numbers, returns {{1}} if {{N}} is positive, {{-1}} if {{N}}146is negative or {{0}} if {{N}} is zero. {{signum}} is exactness147preserving.148149For complex numbers, returns a complex number of the same angle but150with magnitude 1.151152153=== Weak pairs154155''Weak pairs'' behave identically to regular pairs, with one156exception: the car value may be garbage collected. When that happens,157it gets replaced with a sentinel "broken-weak-pointer" value.158159They are indistinguishable from regular pairs: {{car}}, {{cdr}}, etc160all work on them, {{pair?}} returns true, etc. The {{WRITE}}161representation is identical to regular pairs, so they will be read162back as pairs. In other words, they have no read/write invariance.163164They're the same as regular pairs for all intents and purposes.165However, there's a {{weak-pair?}} predicate which ''can'' distinguish166between regular pairs and weak pairs.167168NOTE: Due to internal limitations, {{set-car!}} on a weak pair169currently may cause it to hold onto the value for one more GC cycle in170some situations.171172==== weak-cons173174<procedure>(weak-cons obj[1] obj[2])</procedure><br>175176Returns a newly allocated weak pair whose car is obj[1] and whose cdr177is obj[2]. The pair is indistinguishable from normal pairs, except as178noted above.179180 (weak-cons 'a '()) ===> (a)181 (weak-cons '(a) '(b c d)) ===> ((a) b c d)182 (weak-cons "a" '(b c)) ===> ("a" b c)183 (weak-cons 'a 3) ===> (a . 3)184 (weak-cons '(a b) 'c) ===> ((a b) . c)185186 (import (chicken gc))187188 (let* ((x '(a b))189 (y (weak-cons x 'c)))190 (gc #t)191 (car x)) ===> (a b)192193 (let ((x (weak-cons '(a b) 'c)))194 (gc #t)195 (car x)) ===> #!bwp196197As the final two examples show, when something ''else'' still holds on198to the value that's stored in the car of a weak pair, it will not be199reclaimed. But if the value is ''only'' referenced by one or more200weak pairs, it is reclaimed and the car of the weak pair is replaced201with the ''broken-weak-pointer'' value {{#!bwp}}.202203<procedure>(weak-pair? obj)</procedure><br>204205This predicate returns {{#t}} if and only if {{obj}} is a weak pair.206207 (weak-pair? (weak-cons 'a '())) ===> #t208 (weak-pair? (cons 'a '())) ===> #f209 (weak-pair? (vector 'a '())) ===> #f210211<procedure>(bwp-object? obj)</procedure>212213This predicate returns {{#t}} if {{obj}} is the broken-weak-pointer214value, otherwise {{#f}}.215216217=== Input/Output218219==== current-error-port220221<procedure>(current-error-port [PORT])</procedure>222223Returns default error output port. If {{PORT}} is given, then that224port is selected as the new current error output port.225226Note that the default error output port is not buffered. Use227[[Module (chicken port)#set-buffering-mode!|{{set-buffering-mode!}}]]228if you need a different behaviour.229230==== print231232<procedure>(print [EXP1 ...])</procedure>233234Outputs the optional arguments {{EXP1 ...}} using {{display}} and235writes a newline character to the port that is the value of236{{(current-output-port)}}. Returns {{(void)}}.237238==== print*239240<procedure>(print* [EXP1 ...])</procedure>241242Similar to {{print}}, but does not output a terminating newline243character and performs a {{flush-output}} after writing its arguments.244245246=== Interrupts and error-handling247248==== enable-warnings249250<procedure>(enable-warnings [BOOL])</procedure>251252Enables or disables warnings, depending on wether {{BOOL}} is true or253false. If called with no arguments, this procedure returns {{#t}} if254warnings are currently enabled, or {{#f}} otherwise. Note that this is255not a parameter. The current state (whether warnings are enabled or256disabled) is global and not thread-local.257258259==== error260261<procedure>(error [LOCATION] [STRING] EXP ...)</procedure>262263Prints error message, writes all extra arguments to the value of264{{(current-error-port)}} and invokes the current265exception-handler. This conforms to266[[http://srfi.schemers.org/srfi-23/srfi-23.html|SRFI-23]]. If267{{LOCATION}} is given and a symbol, it specifies the ''location'' (the268name of the procedure) where the error occurred.269270271==== assert272273<macro>(assert EXP [OBJ ...])</macro>274275Evaluates {{EXP}}, if it returns #f, {{error}} is applied to {{OBJ ...}},276else the result of {{EXP}} is returned.277When compiling in unsafe mode, assertions of this kind are disabled.278279280==== get-call-chain281282<procedure>(get-call-chain [START [THREAD]])</procedure>283284Returns a list with the call history. Backtrace information is only285generated in code compiled without {{-no-trace}} and evaluated code.286If the optional argument {{START}} is given, the backtrace starts at287this offset, i.e. when {{START}} is 1, the next to last trace-entry is288printed, and so on. If the optional argument {{THREAD}} is given, then289the call-chain will only be constructed for calls performed by this290thread.291292293294==== print-call-chain295296<procedure>(print-call-chain [PORT [START [THREAD [HEADER]]]])</procedure>297298Prints a backtrace of the procedure call history to {{PORT}}, which299defaults to {{(current-output-port)}}. The output is prefixed by the300{{HEADER}}, which defaults to {{"\n\tCall history:\n"}}.301302303==== procedure-information304305<procedure>(procedure-information PROC)</procedure>306307Returns an s-expression with debug information for the procedure308{{PROC}}, or {{#f}}, if {{PROC}} has no associated debug information.309310311==== warning312313<procedure>(warning MESSAGE [EXP ...])</procedure>314315Displays a warning message (if warnings are enabled with {{enable-warnings}}),316from the {{MESSAGE}}, and optional {{EXP}} arguments, then continues execution.317{{MESSAGE}}, and {{EXP}}, may be {{any}} object.318319320=== Lists321322==== alist-ref323324<procedure>(alist-ref KEY ALIST [TEST [DEFAULT]])</procedure>325326Looks up {{KEY}} in {{ALIST}} using {{TEST}} as the comparison function (or {{eqv?}} if327no test was given) and returns the cdr of the found pair, or {{DEFAULT}} (which defaults to {{#f}}).328329330==== alist-update331332<procedure>(alist-update KEY VALUE ALIST [TEST])</procedure>333<procedure>(alist-update! KEY VALUE ALIST [TEST])</procedure>334335If the list {{ALIST}} contains a pair of the form {{(KEY . X)}}, then this procedure336replaces {{X}} with {{VALUE}} and returns {{ALIST}}. If {{ALIST}} contains no such item, then337{{alist-update}} returns {{((KEY . VALUE) . ALIST)}}. The optional argument338{{TEST}} specifies the comparison procedure to search a matching pair in {{ALIST}}339and defaults to {{eqv?}}. {{alist-update!}} is the destructive version of {{alist-update}}.340341342==== atom?343344<procedure>(atom? X)</procedure>345346Returns {{#t}} if {{X}} is not a pair.347348349==== butlast350351<procedure>(butlast LIST)</procedure>352353Returns a fresh list with all elements but the last of {{LIST}}.354355356==== chop357358<procedure>(chop LIST N)</procedure>359360Returns a new list of sublists, where each sublist contains {{N}}361elements of {{LIST}}. If {{LIST}} has a length that is not362a multiple of {{N}}, then the last sublist contains the remaining363elements.364365<enscript highlight=scheme>366(chop '(1 2 3 4 5 6) 2) ==> ((1 2) (3 4) (5 6))367(chop '(a b c d) 3) ==> ((a b c) (d))368</enscript>369370371==== compress372373<procedure>(compress BLIST LIST)</procedure>374375Returns a new list with elements taken from {{LIST}} with376corresponding true values in the list {{BLIST}}.377378<enscript highlight=scheme>379(define nums '(99 100 110 401 1234))380(compress (map odd? nums) nums) ==> (99 401)381</enscript>382383384==== flatten385386<procedure>(flatten LIST1 ...)</procedure>387388Returns {{LIST1 ...}} concatenated together, with nested lists389removed (flattened).390391392==== foldl393394<procedure>(foldl PROCEDURE INIT LIST)</procedure>395396Applies {{PROCEDURE}} to the elements from {{LIST}}, beginning from397the left:398399<enscript hightlight=scheme>400(foldl + 0 '(1 2 3)) ==> (+ (+ (+ 0 1) 2) 3)401</enscript>402403Note that the order of arguments taken by {{PROCEDURE}} is different404from the {{SRFI-1}} {{fold}} procedure, but matches the more natural405order used in Haskell and Objective Caml.406407408==== foldr409410<procedure>(foldr PROCEDURE INIT LIST)</procedure>411412Applies {{PROCEDURE}} to the elements from {{LIST}}, beginning from413the right:414415<enscript hightlight=scheme>416(foldr + 0 '(1 2 3)) ==> (+ 1 (+ 2 (+ 3 0)))417</enscript>418419420==== intersperse421422<procedure>(intersperse LIST X)</procedure>423424Returns a new list with {{X}} placed between each element.425426427==== join428429<procedure>(join LISTOFLISTS [LIST])</procedure>430431Concatenates the lists in {{LISTOFLISTS}} with {{LIST}} placed432between each sublist. {{LIST}} defaults to the empty list.433434<enscript highlight=scheme>435(join '((a b) (c d) (e)) '(x y)) ==> (a b x y c d x y e)436(join '((p q) () (r (s) t)) '(-)) ==> (p q - - r (s) t)437</enscript>438439{{join}} could be implemented as follows:440441<enscript highlight=scheme>442(define (join lstoflsts #!optional (lst '()))443 (apply append (intersperse lstoflists lst)) )444</enscript>445446447==== rassoc448449<procedure>(rassoc KEY LIST [TEST])</procedure>450451Similar to {{assoc}}, but compares {{KEY}} with the {{cdr}} of each pair in {{LIST}} using452{{TEST}} as the comparison procedures (which defaults to {{eqv?}}).453454455==== tail?456457<procedure>(tail? X LIST)</procedure>458459Returns true if {{X}} is one of the tails (cdr's) of {{LIST}}.460461462=== Vectors463464==== vector-resize465466<procedure>(vector-resize VECTOR N [INIT])</procedure>467468Creates and returns a new vector with the contents of {{VECTOR}} and469length {{N}}. If {{N}} is greater than the original length of470{{VECTOR}}, then all additional items are initialized to {{INIT}}. If471{{INIT}} is not specified, the contents are initialized to some472unspecified value.473474475==== subvector476477<procedure>(subvector VECTOR FROM [TO])</procedure>478479Returns a new vector with elements taken from {{VECTOR}} in the480given range. {{TO}} defaults to {{(vector-length VECTOR)}}.481482{{subvector}} was introduced in CHICKEN 4.7.3.483484485=== Combinators486487488==== constantly489490<procedure>(constantly X ...)</procedure>491492Returns a procedure that always returns the values {{X ...}} regardless of the number and value of its arguments.493494<enscript highlight=scheme>495(constantly X) <=> (lambda args X)496</enscript>497498499==== complement500501<procedure>(complement PROC)</procedure>502503Returns a procedure that returns the boolean inverse of {{PROC}}.504505<enscript highlight=scheme>506(complement PROC) <=> (lambda (x) (not (PROC x)))507</enscript>508509510==== compose511512<procedure>(compose PROC1 PROC2 ...)</procedure>513514Returns a procedure that represents the composition of the515argument-procedures {{PROC1 PROC2 ...}}.516517<enscript highlight=scheme>518(compose F G) <=> (lambda args519 (call-with-values520 (lambda () (apply G args))521 F))522</enscript>523524{{(compose)}} is equivalent to {{values}}.525526527==== conjoin528529<procedure>(conjoin PRED ...)</procedure>530531Returns a procedure that returns {{#t}} if its argument satisfies the532predicates {{PRED ...}}.533<enscript highlight=scheme>534((conjoin odd? positive?) 33) ==> #t535((conjoin odd? positive?) -33) ==> #f536</enscript>537538539==== disjoin540541<procedure>(disjoin PRED ...)</procedure>542543Returns a procedure that returns {{#t}} if its argument satisfies any544predicate {{PRED ...}}.545<enscript highlight=scheme>546((disjoin odd? positive?) 32) ==> #t547((disjoin odd? positive?) -32) ==> #f548</enscript>549550551==== each552553<procedure>(each PROC ...)</procedure>554555Returns a procedure that applies {{PROC ...}} to its arguments, and returns the result(s)556of the last procedure application. For example557558<enscript highlight=scheme>559(each pp eval)560</enscript>561562is equivalent to563564<enscript highlight=scheme>565(lambda args566 (apply pp args)567 (apply eval args) )568</enscript>569570{{(each PROC)}} is equivalent to {{PROC}} and {{(each)}} is equivalent to571{{void}}.572573574==== flip575576<procedure>(flip PROC)</procedure>577578Returns a two-argument procedure that calls {{PROC}} with its579arguments swapped:580<enscript highlight=scheme>581(flip PROC) <=> (lambda (x y) (PROC y x))582</enscript>583584585==== identity586587<procedure>(identity X)</procedure>588589Returns its sole argument {{X}}.590591592==== list-of?593594<procedure>(list-of? PRED)</procedure>595596Returns a procedure of one argument that returns {{#t}} when597applied to a list of elements that all satisfy the predicate procedure598{{PRED}}, or {{#f}} otherwise.599600<enscript highlight=scheme>601((list-of? even?) '(1 2 3)) ==> #f602((list-of? number?) '(1 2 3)) ==> #t603</enscript>604605606==== o607608<procedure>(o PROC ...)</procedure>609610A single value version of {{compose}} (slightly faster). {{(o)}} is equivalent611to {{identity}}.612613614=== User-defined named characters615616==== char-name617618<procedure>(char-name SYMBOL-OR-CHAR [CHAR])</procedure>619620This procedure can be used to inquire about character names or to621define new ones. With a single argument the behavior is as follows:622If {{SYMBOL-OR-CHAR}} is a symbol, then {{char-name}} returns623the character with this name, or {{#f}} if no character is defined624under this name. If {{SYMBOL-OR-CHAR}} is a character, then the625name of the character is returned as a symbol, or {{#f}} if the626character has no associated name.627628If the optional argument {{CHAR}} is provided, then629{{SYMBOL-OR-CHAR}} should be a symbol that will be the new name of630the given character. If multiple names designate the same character,631then the {{write}} will use the character name that was defined last.632633<enscript highlight=scheme>634(char-name 'space) ==> #\space635(char-name #\space) ==> space636(char-name 'bell) ==> #f637(char-name (integer->char 7)) ==> #f638(char-name 'bell (integer->char 7))639(char-name 'bell) ==> #\bell640(char->integer (char-name 'bell)) ==> 7641</enscript>642643644=== The unspecified value645646==== void647648<procedure>(void ARGUMENT ...)</procedure>649650Ignores {{ARGUMENT ...}} and returns an unspecified value.651652653=== Continuations654655==== call/cc656657<procedure>(call/cc PROCEDURE)</procedure>658659An alias for {{call-with-current-continuation}}.660661This procedure is compatible with the definition from the R7RS662{{(scheme base)}} library.663664=== Symbols665666==== Symbol utilities667668===== symbol-append669670<procedure>(symbol-append SYMBOL1 ...)</procedure>671672Creates a new symbol from the concatenated names of the argument symbols673{{(SYMBOL1 ...)}}.674675==== Uninterned symbols ("gensyms")676677Symbols may be "interned" or "uninterned". Interned symbols are678registered in a global table, and when read back from a port are679identical to a symbol written before:680681<enscript highlight=scheme>682(define sym 'foo)683684(eq? sym (with-input-from-string685 (with-output-to-string686 (lambda () (write sym)))687 read))688689 => #t690</enscript>691692Uninterned symbols on the other hand are not globally registered and so693multiple symbols with the same name may coexist:694695<enscript highlight=scheme>696(define sym (gensym 'foo)) ; sym is a uninterned symbol like "foo42"697698(eq? sym (with-input-from-string ; the symbol read will be an interned symbol699 (with-output-to-string700 (lambda () (write sym)))701 read))702703 => #f704705(eq? (string->uninterned-symbol "foo") (string->uninterned-symbol "foo"))706707 => #f708</enscript>709710Use uninterned symbols if you need to generate unique values that711can be compared quickly, for example as keys into a hash-table712or association list. Note that uninterned symbols lose their713uniqueness property when written to a file and read back in, as714in the example above.715716===== gensym717718<procedure>(gensym [STRING-OR-SYMBOL])</procedure>719720Returns a newly created uninterned symbol. If an argument is provided,721the new symbol is prefixed with that argument.722723724===== string->uninterned-symbol725726<procedure>(string->uninterned-symbol STRING)</procedure>727728Returns a newly created, unique symbol with the name {{STRING}}.729730731=== Setters732733SRFI-17 is fully implemented. For more information see:734[[http://srfi.schemers.org/srfi-17/srfi-17.html|SRFI-17]].735736==== setter737738<procedure>(setter PROCEDURE)</procedure>739740Returns the setter-procedure of {{PROCEDURE}}, or signals an error if741{{PROCEDURE}} has no associated setter-procedure.742743Note that {{(set! (setter PROC) ...)}} for a procedure that has no744associated setter procedure yet is a very slow operation (the old745procedure is replaced by a modified copy, which involves a garbage746collection).747748749==== getter-with-setter750751<procedure>(getter-with-setter GETTER SETTER)</procedure>752753Returns a copy of the procedure {{GETTER}} with the associated setter754procedure {{SETTER}}. Contrary to the SRFI specification, the setter755of the returned procedure may be changed.756757758=== Binding forms for optional arguments759760==== optional761762<macro>(optional ARGS DEFAULT)</macro>763764Use this form for procedures that take a single optional argument. If765{{ARGS}} is the empty list {{DEFAULT}} is evaluated and766returned, otherwise the first element of the list {{ARGS}}. It is767an error if {{ARGS}} contains more than one value.768769<enscript highlight=scheme>770(define (incr x . i) (+ x (optional i 1)))771(incr 10) ==> 11772(incr 12 5) ==> 17773</enscript>774775776==== let-optionals777778<macro> (let-optionals ARGS ((VAR1 DEFAULT1) ...) BODY ...)</macro>779780Binding constructs for optional procedure arguments. {{ARGS}} is781normally a rest-parameter taken from a lambda-list. {{let-optionals}}782binds {{VAR1 ...}} to available arguments in parallel, or to783{{DEFAULT1 ...}} if not enough arguments were provided.784{{let-optionals*}} binds {{VAR1 ...}} sequentially, so every variable785sees the previous ones. it is an error if any excess arguments are786provided.787788<enscript highlight=scheme>789(let-optionals '(one two) ((a 1) (b 2) (c 3))790 (list a b c) ) ==> (one two 3)791</enscript>792793==== let-optionals*794795<macro> (let-optionals* ARGS ((VAR1 DEFAULT1) ... [RESTVAR]) BODY ...)</macro>796797Binding constructs for optional procedure arguments. {{ARGS}} is798normally a rest-parameter taken from a lambda-list. {{let-optionals}}799binds {{VAR1 ...}} to available arguments in parallel, or to800{{DEFAULT1 ...}} if not enough arguments were provided.801{{let-optionals*}} binds {{VAR1 ...}} sequentially, so every variable802sees the previous ones. If a single variable {{RESTVAR}} is given,803then it is bound to any remaining arguments, otherwise it is an error804if any excess arguments are provided.805806<enscript highlight=scheme>807(let-optionals* '(one two) ((a 1) (b 2) (c a))808 (list a b c) ) ==> (one two one)809</enscript>810811=== Other binding forms812813==== and-let*814815<macro>(and-let* (BINDING ...) EXP1 EXP2 ...)</macro>816817Bind sequentially and execute body. {{BINDING}} can818be a list of a variable and an expression, a list with a single819expression, or a single variable. If the value of an expression820bound to a variable is {{#f}}, the {{and-let*}} form821evaluates to {{#f}} (and the subsequent bindings and the body822are not executed). Otherwise the next binding is performed. If823all bindings/expressions evaluate to a true result, the body is824executed normally and the result of the last expression is the825result of the {{and-let*}} form. See also the documentation for826[[http://srfi.schemers.org/srfi-2/srfi-2.html|SRFI-2]].827828==== letrec*829830<macro>(letrec* ((VARIABLE EXPRESSION) ...) BODY ...)</macro>831832Implements R6RS/R7RS {{letrec*}}. {{letrec*}} is similar to {{letrec}}833but binds the variables sequentially and is to {{letrec}} what834{{let*}} is to {{let}}.835836This special form is compatible with the definition from the R7RS837{{(scheme base)}} library.838839==== rec840841<macro>(rec NAME EXPRESSION)</macro><br>842<macro>(rec (NAME VARIABLE ...) BODY ...)</macro>843844Allows simple definition of recursive definitions. {{(rec NAME EXPRESSION)}} is845equivalent to {{(letrec ((NAME EXPRESSION)) NAME)}} and {{(rec (NAME VARIABLE ...) BODY ...)}}846is the same as {{(letrec ((NAME (lambda (VARIABLE ...) BODY ...))) NAME)}}.847848==== cut849850<macro>(cut SLOT ...)</macro><br>851<macro>(cute SLOT ...)</macro>852853[[http://srfi.schemers.org/srfi-26/srfi-26.html|Syntactic sugar for specializing parameters]].854855==== define-values856857<macro>(define-values (NAME ...) VALUEEXP)</macro>858<macro>(define-values (NAME1 ... NAMEn . NAMEn+1) VALUEEXP)</macro>859<macro>(define-values NAME VALUEEXP)</macro>860861Defines several variables at once, with the result values of expression862{{VALUEEXP}}, similar to {{set!-values}}.863864This special form is compatible with the definition from the R7RS865{{(scheme base)}} library.866867==== fluid-let868869<macro>(fluid-let ((VAR1 X1) ...) BODY ...)</macro>870871Binds the variables {{VAR1 ...}} dynamically to the values {{X1 ...}}872during execution of {{BODY ...}}. This implements873[[http://srfi.schemers.org/srfi-15/srfi-15.html|SRFI-15]].874875==== let-values876877<macro>(let-values (((NAME ...) VALUEEXP) ...) BODY ...)</macro>878879Binds multiple variables to the result values of {{VALUEEXP ...}}.880All variables are bound simultaneously. Like {{define-values}}, the881{{(NAME ...)}} expression can be any basic lambda list (dotted tail882notation is supported).883884This special form implements885[[http://srfi.schemers.org/srfi-11/srfi-11.html|SRFI-11]], and it is886also compatible with the definition from the R7RS {{(scheme base)}}887library.888889890==== let*-values891892<macro>(let*-values (((NAME ...) VALUEEXP) ...) BODY ...)</macro>893894Binds multiple variables to the result values of {{VALUEEXP ...}}.895The variables are bound sequentially. Like {{let-values}}, the896{{(NAME ...)}} expression can be any basic lambda list (dotted tail897notation is supported).898899This is also part of900[[http://srfi.schemers.org/srfi-11/srfi-11.html|SRFI-11]] and is also901compatible with the definition from the R7RS {{(scheme base)}}902library.903904<enscript highlight=scheme>905(let*-values (((a b) (values 2 3))906 ((p) (+ a b)) )907 p) ==> 5908</enscript>909910==== letrec-values911912<macro>(letrec-values (((NAME ...) VALUEEXP) ...) BODY ...)</macro>913914Binds the result values of {{VALUEEXP ...}} to multiple variables at915once. All variables are mutually recursive. Like {{let-values}}, the916{{(NAME ...)}} expression can be any basic lambda list (dotted tail917notation is supported).918919<enscript highlight=scheme>920(letrec-values (((odd even)921 (values922 (lambda (n) (if (zero? n) #f (even (sub1 n))))923 (lambda (n) (if (zero? n) #t (odd (sub1 n)))) ) ) )924 (odd 17) ) ==> #t925</enscript>926927928==== receive929930<macro>(receive (NAME ...) VALUEEXP BODY ...)</macro><br>931<macro>(receive (NAME1 ... NAMEn . NAMEn+1) VALUEEXP BODY ...)</macro><br>932<macro>(receive NAME VALUEEXP BODY ...)</macro><br>933<macro>(receive VALUEEXP)</macro>934935[[http://srfi.schemers.org/srfi-8/srfi-8.html|SRFI-8]].936Syntactic sugar for {{call-with-values}}. Binds variables937to the result values of {{VALUEEXP}} and evaluates {{BODY ...}},938similar {{define-values}} but lexically scoped.939940{{(receive VALUEEXP)}} is equivalent to {{(receive _ VALUEEXP _)}}.941This shortened form is not described by SRFI-8.942943==== set!-values944945<macro>(set!-values (NAME ...) VALUEEXP)</macro>946<macro>(set!-values (NAME1 ... NAMEn . NAMEn+1) VALUEEXP)</macro>947<macro>(set!-values NAME VALUEEXP)</macro>948949Assigns the result values of expression {{VALUEEXP}} to multiple950variables, similar to {{define-values}}.951952==== nth-value953954<macro>(nth-value N EXP)</macro>955956Returns the {{N}}th value (counting from zero) of the values returned957by expression {{EXP}}.958959960=== Substitution forms and macros961962==== define-constant963964<macro>(define-constant NAME CONST)</macro>965966Defines a variable with a constant value, evaluated at compile-time.967Any reference to such a constant should appear textually '''after'''968its definition. This construct is equivalent to {{define}} when969evaluated or interpreted. Constant definitions should only appear at970toplevel. Note that constants are local to the current compilation971unit and are not available outside of the source file in which they972are defined. Names of constants still exist in the Scheme namespace973and can be lexically shadowed. If the value is mutable, then the974compiler is careful to preserve its identity. {{CONST}} may be any975constant expression, and may also refer to constants defined via976{{define-constant}} previously, but it must be possible to977evaluate the expression at compile-time.978979==== define-inline980981<macro>(define-inline (NAME VAR ...) BODY ...)</macro><br>982<macro>(define-inline (NAME VAR ... . VAR) BODY ...)</macro><br>983<macro>(define-inline NAME EXP)</macro>984985Defines an inline procedure. Any occurrence of {{NAME}} will be replaced986by {{EXP}} or {{(lambda (VAR ... [. VAR]) BODY ...)}}. This is similar987to a macro, but variable names and scope are handled correctly.988989Inline substitutions take place '''after''' macro-expansion, and any990reference to {{NAME}} should appear textually '''after''' its991definition. Inline procedures are local to the current compilation unit992and are not available outside of the source file in which they are993defined. Names of inline procedures still exist in the Scheme namespace994and can be lexically shadowed. Inline definitions should only appear at995the toplevel.996997Note that the {{inline-limit}} compiler option does not affect inline998procedure expansion, and self-referential inline procedures may cause999the compiler to enter an infinite loop.10001001In the third form, {{EXP}} must be a lambda expression.10021003This construct is equivalent to {{define}} when evaluated or1004interpreted.100510061007=== Conditional forms10081009==== unless10101011<macro>(unless TEST EXP1 EXP2 ...)</macro>10121013Equivalent to:10141015<enscript highlight=scheme>1016(if (not TEST) (begin EXP1 EXP2 ...))1017</enscript>10181019==== when10201021<macro>(when TEST EXP1 EXP2 ...)</macro>10221023Equivalent to:10241025<enscript highlight=scheme>1026(if TEST (begin EXP1 EXP2 ...))1027</enscript>10281029=== Record structures10301031==== define-record10321033<macro>(define-record NAME SLOTNAME ...)</macro>10341035Defines a record type. This defines a number of procedures for1036creating, accessing, and modifying record members.10371038Call {{make-NAME}} to create an instance1039of the structure (with one initialization-argument for each slot, in1040the listed order).10411042{{(NAME? STRUCT)}} tests any object for being an instance of this1043structure.10441045Slots are accessed via {{(NAME-SLOTNAME STRUCT)}}1046and updated using {{(NAME-SLOTNAME-set!}} {{STRUCT}} {{VALUE)}}.10471048<enscript highlight=scheme>1049(define-record point x y)1050(define p1 (make-point 123 456))1051(point? p1) ==> #t1052(point-x p1) ==> 1231053(point-y-set! p1 99)1054(point-y p1) ==> 991055</enscript>10561057===== SRFI-17 setters10581059{{SLOTNAME}} may alternatively also be of the form10601061 (setter SLOTNAME)10621063In this case the slot can be read with {{(NAME-SLOTNAME STRUCT)}} as usual,1064and modified with {{(set! (NAME-SLOTNAME STRUCT) VALUE)}} (the slot-accessor1065has an associated SRFI-17 "setter" procedure) instead of1066the usual {{(NAME-SLOTNAME-set!}} {{STRUCT}} {{VALUE)}}.106710681069<enscript highlight=scheme>1070(define-record point (setter x) (setter y))1071(define p1 (make-point 123 456))1072(point? p1) ==> #t1073(point-x p1) ==> 1231074(set! (point-y p1) 99)1075(point-y p1) ==> 991076</enscript>10771078==== define-record-type10791080<macro>(define-record-type NAME (CONSTRUCTOR TAG ...) PREDICATE (FIELD ACCESSOR [MODIFIER]) ...)</macro>10811082SRFI-9 record types. For more information see the documentation for1083[[http://srfi.schemers.org/srfi-9/srfi-9.html|SRFI-9]].10841085As an extension the {{MODIFIER}} may have the form1086{{(setter PROCEDURE)}}, which will define a SRFI-17 setter-procedure1087for the given {{PROCEDURE}} that sets the field value.1088Usually {{PROCEDURE}} has the same name is {{ACCESSOR}} (but it1089doesn't have to).10901091This special form is also compatible with the definition from the R7RS1092{{(scheme base)}} library.10931094==== record-printer10951096<procedure>(record-printer NAME)</procedure><br>10971098Returns the procedure used to print records of the type {{NAME}} if1099one has been set with {{set-record-printer!}}, {{#f}} otherwise.11001101==== set-record-printer!11021103<procedure>(set-record-printer! NAME PROCEDURE)</procedure><br>1104<procedure>(set! (record-printer NAME) PROCEDURE)</procedure>11051106Defines a printing method for record of the type {{NAME}} by1107associating a procedure with the record type. When a record of this1108type is written using {{display, write}} or {{print}}, then1109the procedure is called with two arguments: the record to be printed1110and an output-port.11111112<enscript highlight=scheme>1113(define-record-type foo (make-foo x y z) foo?1114 (x foo-x)1115 (y foo-y)1116 (z foo-z))1117(define f (make-foo 1 2 3))1118(set-record-printer! foo1119 (lambda (x out)1120 (fprintf out "#,(foo ~S ~S ~S)"1121 (foo-x x) (foo-y x) (foo-z x))))1122(define-reader-ctor 'foo make-foo)1123(define s (with-output-to-string1124 (lambda () (write f))))1125s ==> "#,(foo 1 2 3)"1126(equal? f (with-input-from-string1127 s read))) ==> #t1128</enscript>11291130=== Other forms11311132==== load11331134<procedure>(load filename [evalproc])</procedure><br>11351136Filename should be a string naming an existing file containing Scheme1137source code. The load procedure reads expressions and definitions from1138the file and evaluates them sequentially. It is unspecified whether the1139results of the expressions are printed. The load procedure does not1140affect the values returned by current-input-port and1141current-output-port. Load returns an unspecified value.11421143CHICKEN offers a few extensions to the R7RS definition of {{load}}:11441145* The {{filename}} may also be an input port.1146* The expressions which are read one by one from the source file are passed to the procedure indicated by the extra optional {{evalproc}} argument, which defaults to {{eval}}.1147* On platforms that support it (currently BSD, Haiku, MacOS X, Linux, Solaris, and Windows), {{load}} can be used to load shared objects.11481149Example for loading compiled programs:11501151 % cat x.scm1152 (define (hello) (print "Hello!"))1153 % csc -s x.scm1154 % csi -q1155 #;1> (load "x.so")1156 ; loading x.so ...1157 #;2> (hello)1158 Hello!1159 #;3>11601161There are some limitations and caveats to the CHICKEN extensions you1162need to be aware of:11631164* The second argument to {{load}} is ignored when loading compiled code.1165* If source code is loaded from a port, then that port is closed after all expressions have been read.1166* A compiled file can only be loaded once. Subsequent attempts to load the same file have no effect.11671168==== include11691170<macro>(include STRING1 STRING2 ...)</macro>1171<macro>(include-ci STRING1 STRING2 ...)</macro>11721173Include toplevel-expressions from the given source files in the currently1174compiled/interpreted program. If the included file has the extension1175{{.scm}}, then it may be omitted. The file is searched for in the1176current directory and all directories specified by the {{-include-path}}1177option.11781179{{include-ci}} works as {{include}} but reads files in case-insensitive1180mode.11811182==== include-relative11831184<macro>(include-relative STRING)</macro>11851186Works like {{include}}, but the filename is searched for relative to the1187including file rather than the current directory.118811891190=== Making extra libraries and extensions available11911192==== require-extension11931194<macro>(require-extension ID ...)</macro>11951196This is equivalent to {{(require-library ID ...)}} but performs an implicit1197{{import}}, if necessary. Since version 4.4.0, {{ID}} may also be an import specification1198(using {{rename}}, {{only}}, {{except}} or {{prefix}}).11991200To make long matters short - just use {{require-extension}} and it will normally figure everything out for dynamically1201loadable extensions and core library units.12021203This implementation of {{require-extension}} is compliant with [[http://srfi.schemers.org/srfi-55/srfi-55.html|SRFI-55]]1204(see the [[http://srfi.schemers.org/srfi-55/srfi-55.html|SRFI-55]] document for more information).120512061207==== require-library12081209<macro>(require-library ID ...)</macro>12101211This form does all the necessary steps to make the libraries or extensions given1212in {{ID ...}} available. It loads syntactic extensions, if needed and generates1213code for loading/linking with core library modules or separately installed1214extensions.12151216During interpretation/evaluation {{require-library}} performs one of the1217following:12181219* If {{ID}} names a built-in feature, then nothing is done.1220* If {{ID}} names one of the syntactic extensions {{chicken-syntax chicken-ffi-syntax}}, then this extension will be loaded.1221* If {{ID}} names one of the core library units shipped with CHICKEN, then a {{(load-library 'ID)}} will be performed.1222* If {{ID}} names an installed extension with the {{syntax}} or {{require-at-runtime}} attribute, then the extensions is loaded at compile-time, probably doing a run-time {{(require ...)}} for any run-time requirements.1223* Otherwise, {{(require-library ID)}} is equivalent to {{(require 'ID)}}.12241225During compilation, one of the following happens instead:12261227* If {{ID}} names a built-in feature, then nothing is done.1228* If {{ID}} names one of the syntactic extensions {{chicken-syntax chicken-ffi-syntax}}, then this extension will be loaded at compile-time, making the syntactic extensions available in compiled code.1229* If {{ID}} names one of the core library units shipped with CHICKEN, or if the option {{-uses ID}} has been passed to the compiler, then a {{(declare (uses ID))}} is generated.1230* If {{ID}} names an installed extension with the {{syntax}} or {{require-at-runtime}} attribute, then the extension is loaded at compile-time, and code is emitted to {{(require ...)}} any needed run-time requirements.1231* Otherwise {{(require-library ID)}} is equivalent to {{(require 'ID)}}.12321233{{ID}} should be a pure extension name and should not contain any path prefixes (for example {{dir/lib...}} is illegal).12341235{{ID}} may also be a list that designates an extension-specifier. Currently the following extension specifiers are1236defined:12371238* {{(srfi NUMBER ...)}} is required for SRFI-55 compatibility and is fully implemented1239* {{(version ID NUMBER)}} is equivalent to {{ID}}, but checks at compile-time whether the extension named {{ID}} is installed and whether its version is equal or higher than {{NUMBER}}. {{NUMBER}} may be a string or a number, the comparison is done lexicographically (using {{string>=?}}).12401241=== Process shutdown12421243==== emergency-exit12441245<procedure>(emergency-exit [CODE])</procedure>12461247Exits the current process without flushing any buffered output (using1248the C function {{_exit}}). Note that the {{exit-handler}} is not called1249when this procedure is invoked. The optional exit status code {{CODE}}1250defaults to {{0}}.125112521253==== exit12541255<procedure>(exit [CODE])</procedure>12561257Exit the running process and return exit-code, which defaults to 01258(Invokes {{exit-handler}}).12591260Note that pending {{dynamic-wind}} thunks are ''not'' invoked when exiting your program in this way.126112621263=== exit-handler12641265<parameter>(exit-handler)</parameter>12661267A procedure of a single optional argument. When {{exit}} is called,1268then this procedure will be invoked with the exit-code as argument. The1269default behavior is to terminate the program.12701271Note that this handler is ''not'' invoked when {{emergency-exit}} is1272used.127312741275=== implicit-exit-handler12761277<parameter>(implicit-exit-handler)</parameter>12781279A procedure of no arguments. When the last toplevel expression of the1280program has executed, then the value of this parameter is called. The1281default behaviour is to invoke all pending finalizers.128212831284==== on-exit12851286<procedure>(on-exit THUNK)</procedure>12871288Schedules the zero-argument procedures {{THUNK}} to be executed before1289the process exits, either explicitly via {{exit}} or implicitly after1290execution of the last top-level form. Note that finalizers for1291unreferenced finalized data are run before exit procedures.129212931294=== System interface129512961297==== sleep12981299<procedure>(sleep SECONDS)</procedure>13001301Puts the program to sleep for {{SECONDS}}. If the scheduler is loaded1302(for example when srfi-18 is in use) then only the calling thread is put1303to sleep and other threads may continue executing. Otherwise, the whole1304process is put to sleep.130513061307=== File Input/Output13081309==== flush-output13101311<procedure>(flush-output [PORT])</procedure>13121313Write buffered output to the given output-port. {{PORT}} defaults1314to the value of {{(current-output-port)}}.13151316=== Port predicates13171318==== port-closed?13191320<procedure>(port-closed? PORT)</procedure>13211322Is the given {{PORT}} closed (in all directions)?132313241325=== Built-in parameters13261327Certain behavior of the interpreter and compiled programs can be1328customized via the following built-in parameters:13291330==== case-sensitive13311332<parameter>(case-sensitive)</parameter>13331334If true, then {{read}} reads symbols and identifiers in1335case-sensitive mode and uppercase characters in symbols are printed1336escaped. Defaults to {{#t}}.133713381339==== keyword-style13401341<parameter>(keyword-style)</parameter>13421343Enables alternative keyword syntax, where {{STYLE}} may be either1344{{#:prefix}} (as in Common Lisp), which recognizes symbols beginning1345with a colon as keywords, or {{#:suffix}} (as in DSSSL), which recognizes1346symbols ending with a colon as keywords.1347Any other value disables the alternative syntaxes. In the interpreter1348the default is {{#:suffix}}.134913501351==== parentheses-synonyms13521353<parameter>(parentheses-synonyms)</parameter>13541355If true, then the list delimiter synonyms {{#\[}} {{#\]}} and {{#\{}} {{#\}}} are enabled. Defaults to {{#t}}.135613571358==== symbol-escape13591360<parameter>(symbol-escape)</parameter>13611362If true, then the symbol escape {{#\|}} {{#\|}} is allowed when reading1363and printing expressions. Defaults to {{#t}}.136413651366---1367Previous: [[Module srfi-4]]13681369Next: [[Module (chicken bitwise)]]