On Tue, 16 Jan 2001, Fritz Ruehr wrote:
Erik Meijer said:
Not many other imperative languages have statements as first class citizens.
I don't have the details here (e.g., an Algol 68 report), but Michael Scott reports in his "Programming Language Pragmatics" text (p. 279) that:
"Algol 68 [allows], in essence, indexing into an array of statements, but the syntax is rather cumbersome."
Well, there are two ways it allows this. 1) The case statement is little more than array indexing case <int> in <stmt1>, <stmt2>, ... out <other statement> esac 2) You can create an array of procedures returning void results, for which if I remember correctly you have to write VOID: <stmt> to turn the <stmt> into a proc void. You can certainly index an array of these and the relevant proc will be called as soon as the indexing happens (you don't need to write () or anything). So (VOID: print ("a"), VOID: print ("b"))[2] would print "b". I can't remember if you need to specify the type of the array, though. The statements aren't first class, though, because their scope is restricted by the scope of variables that they reference. So begin [10] proc void x; # declare an array of procs # begin int n := 42; x[1] := void: (print (n)) end; x[1] end is invalid because at x[1] it would call the procedure, which would refer to n, which is out of scope (and quite possibly because of sundry syntax errors!). So Algol 68 isn't a counterexample to Erik's claim.
This is in reference to historical variations on switch-like statements (and consistent with a running theme, typical in PL texts, about the extremes of orthogonality found in Algol 68).
Although if they'd really wanted to be extreme they could have left out integer case clauses, because they are the same as indexing a [] proc void! Jón -- Jón Fairbairn Jon.Fairbairn@cl.cam.ac.uk 31 Chalmers Road jf@cl.cam.ac.uk Cambridge CB1 3SZ +44 1223 570179 (pm only, please)