[Swift-user] swift understanding/tutorial

[Daniel S. Katz]

Hi,

I'm just working through the swift examples in the tutorial (http://www.ci.uchicago.edu/swift/guides/tutorial.php).  Some thoughts/comments follow...




This is confusing to me.  If the "file to use" is t, it feels to me that t should be an input parameter, as it tells greeting where to write its output.

It seems that the following should work:

type messagefile;

app () greeting(messagefile t) {
    echo "Hello, world!" stdout=@filename(t);
}

messagefile outfile <"hello.txt">;

greeting(outfile );


but it doesn't, as it appears procedures require a return value.

So I next tried the following, which seemed like it should work:

type messagefile;
int useless;

app (int x) greeting(messagefile t) { 
    echo "Hello, world!" stdout=@filename(t);
}

messagefile outfile <"hello.txt">;

useless = greeting(outfile );


but it also didn't, at least not when hello.txt doesn't already exist.  The command and output are:

tmp:swift dsk$ swift check.swift 
Swift 0.9 swift-r2860 cog-r2388

RunID: 20101014-1003-tq1hn851
Progress:
Failed to transfer wrapper log from check-20101014-1003-tq1hn851/info/4 on localhost
Progress:  Stage in:1
Failed to transfer wrapper log from check-20101014-1003-tq1hn851/info/6 on localhost
Progress:  Stage in:1
Failed to transfer wrapper log from check-20101014-1003-tq1hn851/info/8 on localhost
Execution failed:
	Exception in echo:
Arguments: [Hello, world!]
Host: localhost
Directory: check-20101014-1003-tq1hn851/jobs/8/echo-8dycd50k
stderr.txt: 

stdout.txt: 

----

Caused by:
	File not found: /Users/dsk/Desktop/swift-0.9/examples/swift/./hello.txt


So, clearly there is something about Swift that I'm missing, and that I'm not gathering from the tutorial web page.

I'm writing this with two goals - first, to figure out what basic concept I'm missing, and second, to perhaps expand the tutorial web page so that others don't have this issue.

Thanks.
Dan

-- 
Daniel S. Katz
University of Chicago
(773) 834-7186 (voice)
(773) 834-3700 (fax)
d.katz at ieee.org or dsk at ci.uchicago.edu
http://www.ci.uchicago.edu/~dsk/




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