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Greg Hendershott 2012-10-31 17:16:34 -04:00
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@ -7,7 +7,8 @@
(for-syntax racket/base) (for-syntax racket/base)
(for-label racket) (for-label racket)
(for-label racket/stxparam) (for-label racket/stxparam)
(for-label syntax/parse)) (for-label syntax/parse)
(for-label racket/splicing))
@(define evaluator @(define evaluator
(parameterize ([sandbox-output 'string] (parameterize ([sandbox-output 'string]
[sandbox-error-output 'string]) [sandbox-error-output 'string])
@ -16,14 +17,18 @@
@(define-syntax-rule (i body ...) @(define-syntax-rule (i body ...)
(interaction #:eval evaluator body ...)) (interaction #:eval evaluator body ...))
@image["fear-of-macros.jpg"]
@title[#:version ""]{Fear of Macros} @title[#:version ""]{Fear of Macros}
@author[@hyperlink["https://github.com/greghendershott/fear-of-macros/issues" @author[@hyperlink["http://www.greghendershott.com"
"Greg Hendershott"]] "Greg Hendershott"]]
@smaller{Copyright (c) 2012 by Greg Hendershott. All rights reserved.} @image["fear-of-macros.jpg"]
@para[@smaller{Copyright (c) 2012 by Greg Hendershott. All rights reserved.}]
@para[@smaller["Last updated " @para[@smaller["Last updated "
(parameterize ([date-display-format 'iso-8601]) (parameterize ([date-display-format 'iso-8601])
(date->string (current-date) #t))]] (date->string (current-date) #t))]]
@para{Feedback and corrections are @hyperlink["https://github.com/greghendershott/fear-of-macros/issues" "welcome here"].}
Contents:
@table-of-contents{} @table-of-contents{}
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@ -109,6 +114,7 @@ similar for macro. There is. One of the more-recent Racket macro
enhancements is @racket[syntax-parse]. enhancements is @racket[syntax-parse].
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{Transformers} @section{Transformers}
@ -217,6 +223,7 @@ When Racket expands our program, it sees the occurrence of
calls our function with the old syntax, and we return the new syntax, calls our function with the old syntax, and we return the new syntax,
which is used to evaluate and run our program. which is used to evaluate and run our program.
@; ----------------------------------------------------------------------------
@subsection{What's the input?} @subsection{What's the input?}
@ -298,6 +305,9 @@ When we want to transform syntax, we'll generally take the pieces we
were given, maybe rearrange their order, perhaps change some of the were given, maybe rearrange their order, perhaps change some of the
pieces, and often introduce brand-new pieces. pieces, and often introduce brand-new pieces.
@; ----------------------------------------------------------------------------
@subsection{Actually transforming the input} @subsection{Actually transforming the input}
Let's write a transformer function that reverses the syntax it was Let's write a transformer function that reverses the syntax it was
@ -342,6 +352,7 @@ compiler, and @italic{that} syntax is evaluated:
(values "i" "am" "backwards") (values "i" "am" "backwards")
] ]
@; ----------------------------------------------------------------------------
@subsection{Compile time vs. run time} @subsection{Compile time vs. run time}
@ -509,6 +520,8 @@ So let's try that:
(our-if-using-match-v2 #t "true" "false") (our-if-using-match-v2 #t "true" "false")
] ]
@; ----------------------------------------------------------------------------
@subsection{@racket[begin-for-syntax]} @subsection{@racket[begin-for-syntax]}
We used @racket[for-syntax] to @racket[require] the We used @racket[for-syntax] to @racket[require] the
@ -577,6 +590,7 @@ them available at compile time.}
} }
] ]
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{Pattern matching: syntax-case and syntax-rules} @section{Pattern matching: syntax-case and syntax-rules}
@ -655,6 +669,8 @@ Sometimes, we need to go a step beyond the pattern and template. Let's
look at some examples, how we can get confused, and how to get it look at some examples, how we can get confused, and how to get it
working. working.
@; ----------------------------------------------------------------------------
@subsection{"A pattern variable can't be used outside of a template"} @subsection{"A pattern variable can't be used outside of a template"}
Let's say we want to define a function with a hyphenated name, a-b, Let's say we want to define a function with a hyphenated name, a-b,
@ -1072,6 +1088,7 @@ it
] ]
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{Robust macros: syntax-parse} @section{Robust macros: syntax-parse}
@ -1082,14 +1099,17 @@ TO-DO.
TO-DO. TO-DO.
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{What's the point of @racket[racket/splicing]?} @section{What's the point of @racket[splicing-let]?}
I stared at @racket[racket/splicing] for the longest time, not I stared at @racket[racket/splicing] for the longest time. What does
understanding exactly how it works, or why I'd want to use it. As with it do? Why would I use it? Why is it in the Macros section of the
other aspects of Racket macros, step number one was to de-mythologize reference?
it. This:
Step one, @elem[#:style "strike"]{cut a hole in the box}
de-mythologize it. For example, using @racket[splicing-let] like this:
@#reader scribble/comment-reader @#reader scribble/comment-reader
(i (i
@ -1103,7 +1123,7 @@ it. This:
x x
) )
is shorthand for this: is equivalent to:
@#reader scribble/comment-reader @#reader scribble/comment-reader
(i (i
@ -1118,10 +1138,10 @@ y
) )
This is the classic Lisp/Scheme/Racket idiom sometimes called "let This is the classic Lisp/Scheme/Racket idiom sometimes called "let
over lambda". @margin-note*{A over lambda". @margin-note*{A
@hyperlink["http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/msg03277.html" "koan"] @hyperlink["http://people.csail.mit.edu/gregs/ll1-discuss-archive-html/msg03277.html" "koan"]
about closures and objects.} A closure hides @racket[y], which can't about closures and objects.} A closure hides @racket[y], which can
be accessed directly, only via @racket[get-y]. only be accessed via @racket[get-y].
So why would we care about the splicing forms? They can be more So why would we care about the splicing forms? They can be more
concise, especially when there are multiple body forms: concise, especially when there are multiple body forms:
@ -1154,7 +1174,7 @@ The splicing variation is more convenient than the usual way:
When there are many body forms---and you are generating them in a When there are many body forms---and you are generating them in a
macro---the splicing variations can be much easier. macro---the splicing variations can be much easier.
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{References and Acknowledgments} @section{References and Acknowledgments}
@ -1201,6 +1221,7 @@ projected between the lines. My point is, the Racket documentation is
very good. The @italic{Guide} provides helpful examples and very good. The @italic{Guide} provides helpful examples and
tutorials. The @italic{Reference} is very clear and precise. tutorials. The @italic{Reference} is very clear and precise.
@; ----------------------------------------------------------------------------
@; ---------------------------------------------------------------------------- @; ----------------------------------------------------------------------------
@section{Epilogue} @section{Epilogue}
@ -1218,7 +1239,6 @@ later translated by D.T. Suzuki in his @italic{Essays in Zen
Buddhism}.} Buddhism}.}
} }
Translated into Racket: Translated into Racket:
@racketblock[ @racketblock[
@ -1231,4 +1251,5 @@ Translated into Racket:
(lambda () (lambda ()
(and (eq? 'mountains 'mountains) (and (eq? 'mountains 'mountains)
(eq? 'rivers 'rivers)))) (eq? 'rivers 'rivers))))
] ]