On 19 September 2014 06:05, Richard A. O'Keefe <ok@cs.otago.ac.nz> wrote:

drink (NewGlass i) j = (NewGlass i) -- Eq 1
drink (Fill m i) j
| full (Fill m i) = Fill (NewGlass (size m)) ((size m) - j) -- Eq 2
| i >= j = Fill m (i-j)
| otherwise = drink m (j-1)

First, (Fill m i) isn't *any* kind of constructor.
Second, the first occurrence of (Fill m i) is a (data) pattern
containing the (data) constructor Fill, and the second occurrence
of (Fill m i) is an expression containing the (data) constructor
Fill. We may not know what Glass, NewGlass, and Fill *mean*,
but we know what they *are* (as Haskell thingies).

Your response has clarified most of my confusion.
Please bear with my naivety as seek to ride my mind of confusion over these two point:

1) I do not know what the phrase "(Fill m i) isn't *any* kind of constructor." means.

2) Does "Fill (NewGlass (size m)) ((size m) - j) " create two Glass Haskell thingies?

The context of this code is an attempt to formalize the drinking operation[1].
[1] www.ncgia.ucsb.edu/Publications/Tech_Reports/95/95-7.pdf

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