@node Guile Scheme concepts
@chapter Guile Scheme concepts

Most Scheme implementations go beyond what is specified in the R4RS
document @footnote{Remember?  R4RS is the Revised^4 report on the
Algorithmic Language Scheme}, mostly because R4RS does not give
specifications (or even recommendations) regarding some issues that are
quite important in practical programming.

Here is a list of how Guile implements some of these much-needed Scheme
extensions; other Scheme implementations do so quite similarly.

@menu
* Scheme slang::                
* Read-eval-print loops::       
* Extra data types::            
* Miscellaneous features::      
@end menu

@node Scheme slang
@section Scheme slang
@cindex slang

Even if you read some of the nice books on Scheme, or the R4RS report,
you might not find some of the terms frequently used by Scheme hackers,
both in the manual and in the @url{news:comp.lang.scheme} newsgroup.

Here is a glossary of some of the terms that make Scheme beginners and
intermediate users say ``huh?''

@table @strong
@item thunk
@cindex thunk
A Scheme procedure that takes no arguments.  In this example,
@code{thunk} and @code{another-thunk} are both thunks:
@lisp
(define (thunk)
  (display "Dude, I'm a thunk!")
  (newline))
(define another-thunk
  (lambda ()
    (display "Me too!\n")
    (newline)))
@end lisp

@item closure
@cindex closure
A closure is a procedure.  However, the term emphasizes the fact that a
Scheme procedure remembers (or @dfn{closes over}) the variables that
were visible when the @code{lambda} expression was
evaluated.

In the example below, we might refer to @code{q} as a closure, because
it has closed over the value of @code{x}:
@lisp
(define p
  (lambda (x)
    (lambda (y)
      (+ x y))))
(define q (p 5.7))

(q 10)
@result{} 15.7
@end lisp

However, strictly speaking, every Scheme procedure is really a closure,
since it closes over the top-level environment.

@item alist
@itemx association list

@item plist
@itemx property list

@end table


@node Read-eval-print loops
@section Read-eval-print loops
@cindex Read-eval-print loop
@cindex REPL

To explicitly mention the Scheme read-eval-print loop (REPL) seems weird
because we are all accustomed to firing up an interpreter and having it
read and execute commands.

But the REPL is not specified in R4RS; rather, it is proposed by the
Scheme Bible @cite{Structure and Interpretation of Computer Programs}
(also known as @emph{SICP}), and implemented in some form in all Scheme
interpreters.
@cindex Structure and Interpretation of Computer Programs
@cindex SICP

[FIXME: Someone needs to tell me what needs to be said about Guile's
REPL.]

@node Extra data types
@section Extra data types

The fundamental Scheme data types specified in R4RS are @emph{numbers}
(both exact and inexact), @emph{characters}, @emph{strings},
@emph{symbols}, @emph{vectors}, @emph{pairs} and @emph{lists} [FIXME: is
this complete?].

Many Scheme interpreters offer more types, and Guile is no exception.
Guile is based on Aubrey Jaffer's SCM interpreter, and thus inherits
@emph{uniform arrays}, [FIXME: any others?  How about records?].

On top of that, Guile allows you to add extra types, but that is covered
in @ref{Adding types to Guile}.  Here I will simply document all the
extra Scheme types shipped with Guile.

@menu
* Conventional arrays::         
* Uniform arrays::              
* Bit vectors::                 
* Complex numbers::             
@end menu

@node Conventional arrays
@subsection Conventional arrays

@node Uniform arrays
@subsection Uniform arrays
@cindex arrays - uniform

The motivation for uniform arrays in Scheme is performance.  A vector
provides a performance increase over lists when you want a fixed-size
indexable list.  But the elements in a vector can be of different types,
and this makes for larger storage requirements and slightly lower
performance.

A uniform array is similar to a vector, but all elements have to be of
the same type.

arrays, uniform arrays, bit vectors:

@deffn procedure array-fill ra fill
@end deffn
@deffn procedure serial-array-copy! src dst
@end deffn
@deffn procedure serial-array-map ra0 proc [lra]
@end deffn
@deffn procedure array-map ra0 proc [lra]
@end deffn
@deffn procedure array-for-each proc ra0 [lra]
@end deffn
@deffn procedure array-index-map! ra proc
@end deffn
@deffn procedure array-copy! src dst
@end deffn
@deffn procedure array-copy! src dst
@end deffn
@deffn procedure array-copy! src dst
@end deffn
@deffn procedure array-copy! src dst
@end deffn
@deffn procedure array-copy! src dst
@end deffn
@deffn procedure array? ra [prot]
@end deffn
@deffn procedure array-rank ra
@end deffn
@deffn procedure array-dimensions ra
@end deffn
@deffn procedure dimensions->uniform-array dims prot fill ...
@end deffn
@deffn procedure make-shared-array ra mapfunc dims ...
@end deffn
@deffn procedure transpose-array arg ...
@end deffn
@deffn procedure enclose-array axes ...
@end deffn
@deffn procedure array-in-bounds? arg ...
@end deffn
@deffn procedure array-ref ra arg ..
@end deffn
@deffn procedure uniform-vector-ref vec pos
@end deffn
@deffn procedure array-set! ra obj arg ...
@end deffn
@deffn procedure uniform-array-set1! ua obj arg
@end deffn
@deffn procedure array-contents ra [strict]
@end deffn
@deffn procedure uniform-array-read! ra [port-or-fd] [start] [end]
@end deffn
@deffn procedure uniform-array-write! ra [port-or-fd] [start] [end]
@end deffn
@deffn procedure bit-count item seq
@end deffn
@deffn procedure bit-position item v k
@end deffn
@deffn procedure bit-set! v kv obj
@end deffn
@deffn procedure bit-count* v kv obj
@end deffn
@deffn procedure bit-invert v
@end deffn
@deffn procedure array->list ra
@end deffn
@deffn procedure list->uniform-array ndim prot list
@end deffn
@deffn procedure array-prototype ra
@end deffn

Uniform arrays can be written and read, but @code{read} won't recognize
them unless the optional @code{read-sharp} parameter is supplied,
e.g, 
@smalllisp
(read port #t read-sharp)
@end smalllisp

where @code{read-sharp} is the default procedure for parsing extended
sharp notations.

Reading an array is not very efficient at present, since it's implemented
by reading a list and converting the list to an array.

@c FIXME: must use @deftp, but its generation of TeX code is buggy.
@c Must fix it when TeXinfo gets fixed.
@deftp {Scheme type} {uniform array}

@end deftp

@node Bit vectors
@subsection Bit vectors

@node Complex numbers
@subsection Complex numbers

@c FIXME: must use @deftp, but its generation of TeX code is buggy.
@c Must fix it when TeXinfo gets fixed.
@deftp {Scheme type} complex
Standard complex numbers.
@end deftp

@node Miscellaneous features
@section Miscellaneous features

@defun defined? symbol
Returns @code{#t} if a symbol is bound to a value, @code{#f} otherwise.
This kind of procedure is not specified in R4RS because @c FIXME: finish
this thought
@end defun

@defun object-properties OBJ
and so forth
@end defun