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author | Ludovic Courtès <ludo@gnu.org> | 2010-12-16 15:14:33 +0100 |
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committer | Ludovic Courtès <ludo@gnu.org> | 2010-12-16 23:45:23 +0100 |
commit | 18f06db925a67cb6b174a9210f7bed8adced4e00 (patch) | |
tree | a4ca1837512a3c5a0f179d4f38f740f4792af601 /doc/ref/api-procedures.texi | |
parent | 0bfba83a038ba03924eb82841407d387310181d5 (diff) | |
download | guile-18f06db925a67cb6b174a9210f7bed8adced4e00.tar.gz |
Add `compose', `negate', and `const'.
* module/ice-9/boot-9.scm (compose, negate, const): New procedures.
* doc/ref/api-procedures.texi (Higher-Order Functions): New node.
* test-suite/Makefile.am (SCM_TESTS): Add `tests/procs.test'.
* test-suite/tests/procs.test: New file.
Diffstat (limited to 'doc/ref/api-procedures.texi')
-rw-r--r-- | doc/ref/api-procedures.texi | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/doc/ref/api-procedures.texi b/doc/ref/api-procedures.texi index 8fc7f33f5..c087f4c7e 100644 --- a/doc/ref/api-procedures.texi +++ b/doc/ref/api-procedures.texi @@ -13,6 +13,7 @@ * Compiled Procedures:: Scheme procedures can be compiled. * Optional Arguments:: Handling keyword, optional and rest arguments. * Case-lambda:: One function, multiple arities. +* Higher-Order Functions:: Function that take or return functions. * Procedure Properties:: Procedure properties and meta-information. * Procedures with Setters:: Procedures with setters. @end menu @@ -573,6 +574,62 @@ arguments, and on the predicate; keyword arguments may be present but do not contribute to the ``success'' of a match. In fact a bad keyword argument list may cause an error to be raised. +@node Higher-Order Functions +@subsection Higher-Order Functions + +@cindex higher-order functions + +As a functional programming language, Scheme allows the definition of +@dfn{higher-order functions}, i.e., functions that take functions as +arguments and/or return functions. Utilities to derive procedures from +other procedures are provided and described below. + +@deffn {Scheme Procedure} const value +Return a procedure that accepts any number of arguments and returns +@var{value}. + +@lisp +(procedure? (const 3)) @result{} #t +((const 'hello)) @result{} hello +((const 'hello) 'world) @result{} hello +@end lisp +@end deffn + +@deffn {Scheme Procedure} negate proc +Return a procedure with the same arity as @var{proc} that returns the +@code{not} of @var{proc}'s result. + +@lisp +(procedure? (negate number?)) @result{} #t +((negate odd?) 2) @result{} #t +((negate real?) 'dream) @result{} #t +((negate string-prefix?) "GNU" "GNU Guile") + @result{} #f +(filter (negate number?) '(a 2 "b")) + @result{} (a "b") +@end lisp +@end deffn + +@deffn {Scheme Procedure} compose proc rest ... +Compose @var{proc} with the procedures in @var{rest}, such that the last +one in @var{rest} is applied first and @var{proc} last, and return the +resulting procedure. The given procedures must have compatible arity. + +@lisp +(procedure? (compose 1+ 1-)) @result{} #t +((compose sqrt 1+ 1+) 2) @result{} 2.0 +((compose 1+ sqrt) 3) @result{} 2.73205080756888 +(eq? (compose 1+) 1+) @result{} #t + +((compose zip unzip2) '((1 2) (a b))) + @result{} ((1 2) (a b)) +@end lisp +@end deffn + +@deffn {Scheme Procedure} identity x +Return X. +@end deffn + @node Procedure Properties @subsection Procedure Properties and Meta-information |