[mercury-users] Mercury needs a Tutorial

[David Powers]

Looks good - I'll keep comments/corrections brief.

In your program you have

:- import_module io.

In your explanation you have

:- use_module io.


The idea of programs having input/output parameters will be familiar to those 
who learnt strict Jensen&Wirth Pascal (program asdf(input,output)).


Is "token" the appropriate word to describe "__" (something higher level
like operator perhaps)?

Rather than "some punctuation symbol" how about "something non-alphabetic" 
(e.g. numbers start with digits).

"Think mathematically and you'll be fine!" is the last thing I would say to my 
students...  They'd run a mile...

Most examples came out centred (line by line), which looks a bit strange...  I 
guess this'll work out in the wash, or it may be exmh (I see you did centre 
tables - the part before <p> was centred within the table, while the part 
afterwards was indented as well as can be expected as I saw in the fibonacci 
example).

Given that doing the factorial examples like this in Prolog would
return the sum of the appropriate number of 1's, do I assume that = acts like 
Prolog's is and evaluates expressions.  Moreoever the fibonacci example would 
fail due to predicates not being evaluated and the non-existence of functions.  
Interesting.  It may be worth explicitly highlighting differences from Prolog 
like this.  The use of {...} needs to be spelled out a little more explicitly, 
at least actually quoting the relevant line rather than expecting the reader to 
look back, hunt for the braces (hard in my font) and figure what you are 
talking about and why (--> adds to all predicates, not functions in both head 
and tail and factorial doesn't do I/O and the definition doesn't have I/O 
arguments.  I'm a Prolog programmer and NL expert, and I had to make a little 
effort to connect your {...} comment with the DCG shorthand and had skimmed 
past them without noticing. (Unlike those who suggested that introducing DCG 
notation in your first example was too much, I think it is appropriate to show 
the simpler surface form.)

In teaching Prolog I strongly discourage use of ; (probably pretty common), and 
also -> ; (less common).  Possibly it is only the nesting of these I should 
discourage, particularly as there are optimizations which are lost by doing so. 
It may be worth commenting on this (to Prolog programmers) if there are special 
reasons why these are used in Mercury where they would not be in Prolog.

So far so good...

Thanks for the effort, Looking forward to the next installment!

David
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