Re: Module Behavior
- To: mathgroup at smc.vnet.net
- Subject: [mg84680] Re: [mg84660] Module Behavior
- From: Carl Woll <carlw at wolfram.com>
- Date: Wed, 9 Jan 2008 03:50:23 -0500 (EST)
- References: <200801080837.DAA04375@smc.vnet.net>
Marcelo Mayall wrote:
>One of the main features of the function Module is that you can specify
>symbols to be treated as local. For example:
>
>In[1]:= Module[{a, b}, a = b; b = 1;]
>In[2]:= {Names["a$*"], Names["b$*"]}
>
>Out[2]= {{}, {}}
>
>However, if we change the local symbol "b" to "b[1]" it does not treat
>as local anymore.
>
>In[3]:= Module[{a, b}, a = b[1]; b[1] = 1;]
>In[4]:= {Names["a$*"], Names["b$*"]}
>
>Out[4]= {{}, {"b$69"}}
>
>
The difference here is that you are giving a an own value, while you are
giving b a down value. If a Temporary variable has only OwnValues
definitions, it is removed at the end of a Module. If a Temporary
variable has any DownValues definitions, the variable persists.
Carl Woll
Wolfram Research
>And each time you execute this command line a new variable "b$*" will be
>created.
>
>In[14]:= Module[{a, b}, a = b[1]; b[1] = 1;]
>In[15]:= {Names["a$*"], Names["b$*"]}
>
>Out[15]= {{}, {"b$69", "b$77", "b$79", "b$81", "b$84", "b$86", "b$88",
>"b$90", "b$92", "b$94"}}
>
>
>Shouldn't the function Module treat the symbol "b[1]" as local too?
>Is this an expected or unexpected result?
>
>Regards,
>Marcelo Mayall
>
>
>
- References:
- Module Behavior
- From: "Marcelo Mayall" <mmayall@bol.com.br>
- Module Behavior