| Bug or desired behavior in lambda functions? [message #91136] |
Mon, 08 June 2015 10:34  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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Hello,
Despite what the documentation might suggest, and one might expect, it seems there is no way to use string variables to make lambda functions.
If I try to make a lambda function with the code inside lambda(), all is well:
IDL> l=lambda('x: x^2')
IDL> l(2)
4
However, if I put the same code in a string and pass it to lambda, it does not accept the code:
IDL> expr='x: x^2'
IDL> l=lambda(expr)
% LAMBDA: Code must be of the form "arg1,arg2,... : statement"
I expect this is caused by IDL parser's special behavior when it encounters lambda(), which is what allows this
IDL> l=lambda(x: x^2)
So I think when I put a variable name inside the lambda() call, the parser thinks is a string literal, and tries to parse the variable name as code.
Is this intended behavior, or a bug?
Paulo
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| Re: Bug or desired behavior in lambda functions? [message #91140 is a reply to message #91136] |
Mon, 08 June 2015 13:31  |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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The best workaround I found is using call_function:
IDL> expr='x: x^2'
IDL> l=call_function('lambda',expr)
IDL> l(3)
9
On Monday, June 8, 2015 at 2:34:12 PM UTC-3, Paulo Penteado wrote:
> Hello,
>
> Despite what the documentation might suggest, and one might expect, it seems there is no way to use string variables to make lambda functions.
>
> If I try to make a lambda function with the code inside lambda(), all is well:
>
> IDL> l=lambda('x: x^2')
> IDL> l(2)
> 4
>
> However, if I put the same code in a string and pass it to lambda, it does not accept the code:
>
> IDL> expr='x: x^2'
> IDL> l=lambda(expr)
> % LAMBDA: Code must be of the form "arg1,arg2,... : statement"
>
> I expect this is caused by IDL parser's special behavior when it encounters lambda(), which is what allows this
>
> IDL> l=lambda(x: x^2)
>
> So I think when I put a variable name inside the lambda() call, the parser thinks is a string literal, and tries to parse the variable name as code.
>
> Is this intended behavior, or a bug?
>
> Paulo
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| Re: Bug or desired behavior in lambda functions? [message #91146 is a reply to message #91136] |
Tue, 09 June 2015 06:09 |
PMallas
Messages: 2
Registered: June 2015
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Junior Member |
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On Monday, June 8, 2015 at 1:34:12 PM UTC-4, Paulo Penteado wrote:
> Hello,
>
> Despite what the documentation might suggest, and one might expect, it seems there is no way to use string variables to make lambda functions.
>
> If I try to make a lambda function with the code inside lambda(), all is well:
>
> IDL> l=lambda('x: x^2')
> IDL> l(2)
> 4
>
> However, if I put the same code in a string and pass it to lambda, it does not accept the code:
>
> IDL> expr='x: x^2'
> IDL> l=lambda(expr)
> % LAMBDA: Code must be of the form "arg1,arg2,... : statement"
>
> I expect this is caused by IDL parser's special behavior when it encounters lambda(), which is what allows this
>
> IDL> l=lambda(x: x^2)
>
> So I think when I put a variable name inside the lambda() call, the parser thinks is a string literal, and tries to parse the variable name as code.
>
> Is this intended behavior, or a bug?
>
> Paulo
I experimented with the same thing, I found this to work:
IDL> expr='x: x^2
IDL> l=lambda(expr)
% LAMBDA: Code must be of the form "arg1,arg2,... : statement"
% Execution halted at: $MAIN$
IDL> l=lambda(''+expr)
IDL> l(2)
4
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| Re: Bug or desired behavior in lambda functions? [message #91152 is a reply to message #91146] |
Tue, 09 June 2015 08:42 |
penteado
Messages: 866
Registered: February 2018
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Senior Member
Administrator |
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|
Neat trick!
Thanks.
> I experimented with the same thing, I found this to work:
>
> IDL> expr='x: x^2
> IDL> l=lambda(expr)
> % LAMBDA: Code must be of the form "arg1,arg2,... : statement"
> % Execution halted at: $MAIN$
> IDL> l=lambda(''+expr)
> IDL> l(2)
> 4
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