Tcl 8.4 array key setting cannot accept inline function call

Question

In other dynamic typed, interpeted languages (Ruby, PERL...), one can defined a key in a hash as an inline of a function call. For example (in Ruby:

a[ foo(1) ] = bar

I have tried to do the same in Tcl 8.4, but failed, see tclsh log below:

% proc add1 { x } { expr {$x + 1 } }
% array set p {}
% set p( [add1 1]) 0
wrong # args: should be "set varName ?newValue?"

Needsless to say, that I assign a variable to the output of of add1 1, and use the variable value, it does work:

% set a [add1 1]
2
% set p($a) 0
0

It is a style issue, no doubt, but I like inlining functions, and not using intermediate vriables. Any suggestions?

Jerry · Accepted Answer · 2014-08-21 14:47:45Z

5

It's not really 'pretty' as such, but you can use eval to do something like that:

eval "set p([add1 1]) 0"

First, you give the string "set p([add1 1]) 0" to eval and since it is between quotes, you get a first level of substitution: [add1 1] is evaluated before being passed which means the final string passed to eval is set p(2) 0. eval then evaluates this.

EDIT:

Actually, it works without eval too, your error struck me as strange but didn't pay much attention to a detail. You need to remove the space after the first paren:

set p([add1 1]) 0

Otherwise, set interprets that you're giving the two arguments [add1 1]) and 0 to the variable name p(.

edited Aug 21, 2014 at 14:47

answered Aug 21, 2014 at 12:02

Jerry

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2 Comments

user1134991 Over a year ago

Yup, that is what I was looking for... Thanks!

This isn't my real name Over a year ago

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Hai Vu · Accepted Answer · 2014-08-22 03:31:18Z

0

Here is another way it works, which uses array set:

array set p {}
array set p [list [add1 1] 0]
array set p [list [add1 2] 0]
parray p

Output:

p(2) = 0
p(3) = 0

answered Aug 22, 2014 at 3:31

Hai Vu

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