localtime Monks

I stumbled over pugs via the Perl 6 mailing list yesterday. As I had all the prerequisites installed I fetched the darcs repository and compiled it on my XP box at work.

I attempted the following on my windows command line:

C:\dev\fun\pugs>pugs -e "sub hi { \"Hello, \" ~ $_ } ; hi( \"Perl 6!\n
+\" )"
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This gave me my very first working Perl 6 script! Wohoo! It also gave me the syntax-tree of the one-liner.:

*** Evl: Syn ";" {{ Syn ":=" {{ Var "&prefix:hi" (line 1, column 8); s
+ub {...} }
}; App "&prefix:hi" [] [Val (VStr "Perl 6!\n")] }}
***  Evl: Syn ":=" {{ Var "&prefix:hi" (line 1, column 8); sub {...} }
+}
***  Ret: sub {...}
***  Evl: App "&prefix:hi" [] [Val (VStr "Perl 6!\n")]
***   Evl: Syn "[]" {{ Syn "," {{ "Perl 6!\n" }}; 0 }}
***    Evl: Syn "," {{ "Perl 6!\n" }}
***    Ret: ("Perl 6!\n")
***   Ret: ("Perl 6!\n")
***   Evl: Syn "[]" {{ Syn "," {{ "Perl 6!\n" }}; (1, ...) }}
***    Evl: Syn "," {{ "Perl 6!\n" }}
***    Ret: ("Perl 6!\n")
***   Ret: ()
***   Evl: Syn ";" {{ App "&infix:~" [] [Val (VStr "Hello, "),Var "$_"
+ (line 1,
column 22)] }}
***    Evl: App "&infix:~" [] [Val (VStr "Hello, "),Var "$_" (line 1, 
+column 22)
]
***     Evl: Var "$_" (line 1, column 22)
***     Ret: ("Perl 6!\n")
***     Evl: Syn "[]" {{ Syn "," {{  }}; (0, ...) }}
***      Evl: Syn "," {{  }}
***      Ret: ()
***     Ret: ()
***    Ret: "Hello, Perl 6!\n"
***   Ret: "Hello, Perl 6!\n"
***  Ret: "Hello, Perl 6!\n"
*** Ret: "Hello, Perl 6!\n"
Hello, Perl 6!
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Dandy! But I couldn't stop yet. I dug up Featherweight Perl, which had some examples translated from "A gentle introduction to Haskell" (which is, I have to admit, not very gentle). This is where I hit a wall. The following code:

multi sub quicksort () { () }
multi sub quicksort ( $x, *@xs ) {
  @xs.grep( { $_ < $x } ).quicksort,
  $x,
  @xs.grep( { $_ >= $x } ).quicksort
}
quicksort(1,5,2,4,3)
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Produces a listing that to me is quite puzzling:

C:\dev\fun\pugs>pugs ex.pl

Fail: cannot cast: VError "\nunexpected \")\"\nexpecting term" (NonTer
+m (line 1, column 27))
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It looks like the parentheses that specify the return value of the function with the empty list arrives as a surprise. I have no idea why this happens, and while I do know that pugs is in flux I'm curious if someone can explain what's going on. I looked at the pugs code, but my Haskell-fu is very weak, so that didn't help me much. (One day, Haskell, I shall master your curried Monads!)

Anyhow. It was a fun little experiment, and it's great to see initiatives like this. Kudos to Autrijus Tang.