Smalltalk, using 'value' on BlockClosure

Question

I am trying to create a method for the existing BlockClosure class. This is a method we wrote on the board in class, but it is not behaving exactly as I'd want it to. This is the code:

BlockClosure extend[
   times: count[
      count = 0
      ifTrue:
      [^self value.]
      ifFalse:
      [self value. self times: count - 1.].
   ]
].

I tried testing it out by inputting this into the gst interpreter:

st> x:= 5
5 
st> y := [x-1] times: 4.
a BlockClosure

But I want y to equal 1 in this case. Why is y's value becoming "a BlockClosure"?

EDIT: The correct times method.

BlockClosure extend[
   times: count[
      count = 0
      ifFalse:
      [self value. ^self times: count - 1.].
   ]
].

score 2 · Accepted Answer · answered Mar 03 '13 at 23:39

2

First of all, you're missing the ^ in the ifFalse: branch of the conditional statement, which is preventing the return value from propagating back from the recursive call:

ifFalse:
[self value. ^self times: count - 1]

Secondly, this will actually set y to 4 instead, because you're computing x - 1 with the same x value each time. What you probably mean to do is reassign back to x each time:

y := [x := x - 1] times: 4

answered Mar 03 '13 at 23:39

Ash Wilson

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Thank you! Turns out it still returns "a BlockClosure", but that is the value of y. If I check the x value though, it has changed. – Isaac Mar 04 '13 at 01:15
It returns a BlockClosure because your fixed "times:" method does not have an explicit return, so it implicitly returns self. – codefrau Mar 04 '13 at 11:55

Smalltalk, using 'value' on BlockClosure

1 Answers1