Learn From The Metsim Example Models
You may wonder if it is really necessary to go into APL in depth to use Metsim well. It depends what you consider "using Metsim well" to be. There are infinite capabilities - how much of it do you want to use?
The most accessible examples for all of us of good use of Metsim are the example models in the c:\METSIM\mex folder. maybe some are old, maybe some have fragments of things that are not used. In the examples Proware demonstrates the basics of good model construction and some use of APL expressions to do specific things. Some of those APL expressions are rather intriguing - we can see what they do, and we can see the promise they are hinting of. You can study some of these expressions and work out what they are doing (and that is how I started to learn some basics of APL), but you soon realise that a parallel approach works better. If you find an APL expression that you like (you can use it, you think you understand it) then why not use it as your incentive to study the few operators in it and make this your starting point for what will be a very productive adventure.
I suspect the first explorers sailing towards the horizon didn't head off expecting to arrive back where they started (they didn't plan to prove the world wasn't flat) - they just pursued a simple achieveable goal - find out what's out there a bit further. The results surprised them. They found what they observed very useful. They changed the way they thought and never looked back.
My experience in learning APL (an ongoing process) is that it is very easy to make some exremely satisfying progress - but then you find you should study the basics properly. Once you know you won't fall off the edge of the world you get more interested in studying - navigation by the stars, prevailing winds and currents, accurate time measurement (for estimating longtitude). Maybe I am using the flat earth analogy of non APL a bit too bluntly. I should move on.
After making some progress with a few APL expressions the hard way, you will find you want to study it in the proper order - using a well written text book, or a course (save time, focus on what you are doing, gain from experience, get alternative explanations, ask questions etc.). In the last few posts I used the comma symbol (the catenate or ravel operator) as an example of an APL symbol that is in plain sight and ran with it over the horizon to find out about describing data structure and re-arranging data etc.
So that is one operator that is better understood. There are not actually many in total - so that is pretty good progress - and many of the difficult concepts (all those repeated phrases) have been dealt with.