Scala way to write lisp-like progn?

Question

Is there in Scala some language construction like lisp's progn?
Thanks!

Please add pseudo scala code with such `progn` you want to evaluate and the result of evaluation. Note that in scala `{a; b; c}` returns result of `c`. — senia, Jan 14 '14 at 12:56

score 5 · Accepted Answer · answered Jan 14 '14 at 13:50

5

Yep, curly braces.

progn evaluates forms, in the order in which they are given.

The values of each form but the last are discarded.

Examples:

 (progn) =>  NIL
 (progn 1 2 3) =>  3
 (progn (values 1 2 3)) =>  1, 2, 3
 (setq a 1) =>  1
 (if a
      (progn (setq a nil) 'here)
      (progn (setq a t) 'there)) =>  HERE
 a =>  NIL

Now the same, but in scala:

scala> {}

// Unit is not written explicitly, but it is here
scala> {1; 2; 3}
// warnings omitted
// res1: Int = 3

scala> {(1, 2, 3)}
// res2: (Int, Int, Int) = (1,2,3)

// no direct analog for setq, skipping other examples

And to ensure you that evaluates forms, in the order in which they are given:

scala> {println('1'); println('2'); println('3')}
1
2
3

answered Jan 14 '14 at 13:50

om-nom-nom

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One more noob question:) What about PROG1, PGOG2? – The Architect Jan 14 '14 at 18:22
I doubt there is built in mechanisms for both. For PROG1 there is an analog (in some sense) -- [function commonly called `tap` (aka kestrel combinator)](http://stackoverflow.com/q/16742060/298389) – om-nom-nom Jan 14 '14 at 18:29
1

@om-nom-nom Both seem to be very easy to implement with Scala macros. – ghik Jan 14 '14 at 19:43
@ghik yeah, but I don't think it is really needed, ordinary scala possibilities will do the job – om-nom-nom Jan 14 '14 at 21:10

Scala way to write lisp-like progn?

1 Answers1