topic Making an associative array with values having expression evaluation results in Discussions

Making an associative array with values having expression evaluation results

miguello — Fri, 09 Jun 2023 16:09:39 GMT

As usual I'm having trouble with Eval and Expr.

I need to create an associative array where values would be evaluated results of some expressions.

For instance I need to create

aaa=[
"2x2" => 4
]

but 4 there is a result of evaluated expression Expr(2*2)

Lame variant that obviously doesn't work is here:

aaa=[
"2x2" => 2*2
]

But then I'll say that 2*2 is an Expr:

aaa=[
"2x2" => Expr(2*2)
]

and then I'll use Eval Expr to evaluate all expressions inside the argument and return expression with evaluated subexpressions:

Eval Expr(
aaa=[
"2x2" => Expr(2*2)
]
)

and it already doesn't work - it doesn't evaluate Expr(2*2)

The next step would be to evaluate resultant expression:

Eval(
Eval Expr(
aaa=[
"2x2" => Expr(2*2)
]
)
)

but obviously it doesn't work.

Why does it not work and what is the correct way?

Re: Making an associative array with values having expression evaluation results

ErraticAttack — Tue, 09 May 2023 23:38:18 GMT

JMP is nothing if not inconsistent. You can do it via lists, which is what I do in these circumstances:

val1 = "Steve";
val2 = "The";
val3 = "Turtle";
aaa = Associative Array(
	{"key1", "key2", "key3"},
	Eval List( {val1, val2, val3} )
);

show( aaa )

Re: Making an associative array with values having expression evaluation results

Craige_Hales — Wed, 10 May 2023 01:10:09 GMT

Why does it not work

The square bracket form is a compile time constant, both for arrays and associative arrays. The constant between the square brackets is cloned at run time and stored into aaa.

@ErraticAttack is the way I'd do it too.

Re: Making an associative array with values having expression evaluation results

ErraticAttack — Wed, 10 May 2023 05:35:20 GMT

@Craige_Hales Good to know! Sounds like you have some behind-the-scenes development experience on this!

Re: Making an associative array with values having expression evaluation results

miguello — Wed, 10 May 2023 18:21:12 GMT

Ok, understood. I thought that it was Associative Array specific, but looks like it is syntax specific :)