Binary matcing
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Alexander Kuleshov
May 12, 2013, 3:44:56 AM5/12/13
to Lisp Flavoured Erlang
Hi all,
I try to write function with lfe which passes binary. How can i match
arg?
For example:
(defun foo (#b 40 rest)
(defun foo ( _ )
'ok)
But i got illegal binary error.
I need something in erlang analog:
foo(<<$40, Rest/binary>>) ->
....;
foo(_) ->
ok.
How can i make it?
Thank you.
I try to write function with lfe which passes binary. How can i match
arg?
For example:
(defun foo (#b 40 rest)
(defun foo ( _ )
'ok)
But i got illegal binary error.
I need something in erlang analog:
foo(<<$40, Rest/binary>>) ->
....;
foo(_) ->
ok.
How can i make it?
Thank you.
rvirding
May 12, 2013, 1:20:51 PM5/12/13
to lisp-flavo...@googlegroups.com
You need to use another format for defun.
On Sunday, May 12, 2013 9:44:56 AM UTC+2, Alexander Kuleshov wrote:
The #b syntax for a binary literal, for example #b(1 2 3). It is equivalent to literal binaries like <<1,2,3>> with byte segments in vanilla erlang.
To get pattern matching in a function definition you need to use another format for defun which allows you define multiple clauses with argument patterns and bodies. It looks like:
(defun foo
(((binary 40 (binary rest))) ...)
((...) ...)
((_) 'ok))
Each clause has the form
((<argpattern> ...) <body expr> ...)
Note there is no argument list for the whole function here! The "classic" defun syntax is valid but only when giving argument variables with no pattern matching, for example:
(defun bar (a b) (+ a b))
So for example you can define the member function as either:
(defun member (x es)
(case es
((cons x _) 'true)
((cons _ es) (member x es))
(() 'false)))
(defun member
((x (cons x . _)) 'true)
((x (cons _ es)) (member x es))
((_ ()) 'false)))
They are equivalent. The first is more classic lisp style but using pattern matching, while the second is more classic erlang style with clauses.
There is a short description of defun's and binary syntax in the doc/user_guide.txt. There are more tutorials, documentation and examples on the LFE page at http://lfe.github.io/ . Definitely check it out!
Robert
On Sunday, May 12, 2013 9:44:56 AM UTC+2, Alexander Kuleshov wrote:
Hi all,
I try to write function with lfe which passes binary. How can i match
arg?
For example:
(defun foo (#b 40 rest)
(defun foo ( _ )
'ok)
But i got illegal binary error.
The #b syntax for a binary literal, for example #b(1 2 3). It is equivalent to literal binaries like <<1,2,3>> with byte segments in vanilla erlang.
I need something in erlang analog:
foo(<<$40, Rest/binary>>) ->
....;
foo(_) ->
ok.
How can i make it?
To get pattern matching in a function definition you need to use another format for defun which allows you define multiple clauses with argument patterns and bodies. It looks like:
(defun foo
(((binary 40 (binary rest))) ...)
((...) ...)
((_) 'ok))
Each clause has the form
((<argpattern> ...) <body expr> ...)
Note there is no argument list for the whole function here! The "classic" defun syntax is valid but only when giving argument variables with no pattern matching, for example:
(defun bar (a b) (+ a b))
So for example you can define the member function as either:
(defun member (x es)
(case es
((cons x _) 'true)
((cons _ es) (member x es))
(() 'false)))
(defun member
((x (cons x . _)) 'true)
((x (cons _ es)) (member x es))
((_ ()) 'false)))
They are equivalent. The first is more classic lisp style but using pattern matching, while the second is more classic erlang style with clauses.
There is a short description of defun's and binary syntax in the doc/user_guide.txt. There are more tutorials, documentation and examples on the LFE page at http://lfe.github.io/ . Definitely check it out!
Robert
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