#inject:into: What a Gem!

Hello Forum,

I just accomplished something in about ten minutes that has taken me
many times that in other languages, even Eiffel. I decided to create a
method in my ActiveTreeModel class that would build a TreeModel from the
bracketed notation of a tree (as explained in Knuth's AoP, Vol. 1). The
bracketed notation is a very efficient way to represent a tree (in most,
but not all, circumstances).

Given the following array,

#(#a #b #(#c #d #e) #f #g #(#h #i #(#j)))

build a tree. It should look like this:

a
b
c
d
e
f
g
h
i
j

I was able to accomplish this with merely the following code:

ActiveTreeModel>>addFromBracketNotation: anArray asChildOf: parent

anArray inject: nil
into:
[:elementBefore :element |
(element isKindOf: Array)
ifTrue:
[self addFromArray: element asChildOf:
elementBefore]
ifFalse: [self add: element asChildOf: parent]]

This kind of parsing is usually a mess in other languages. Smalltalk
just seems to smile and take it all in stride. I expected to have to
spend hours doing this. I think the only reason it took a whopping ten
minutes, instead of five, was due to the need to change from "(element
countElements > 1)" to "(element isKindOf: Array)". I was bitten by the
following scenario:

#(#b) #countElements returns 1.
#c #countElements also returns 1.

Notationally, however, the two are very different.

Cheers,

Eric

.

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