Can not call "function" in GNU Smalltalk

I want to define block and call it in this way:

add := [ :a :b |
    ^(a+b).
].

n := add value: 1 value: 2.

But when I try it, I get an error:

$ gst 3.1.st 
Object: 3 error: return from a dead method context
SystemExceptions.BadReturn(Exception)>>signal (ExcHandling.st:254)
SystemExceptions.BadReturn class(Exception class)>>signal (ExcHandling.st:151)
SmallInteger(Object)>>badReturnError (Object.st:1389)
UndefinedObject>>executeStatements (3.1.st:3)

How can I call a function in GNU Smalltalk?

Well, I dropped the return statement, and this code works fine. But when I try to define more complicated function, for example:

nod := [ :a :b |
    (a=b) ifTrue: [a].
    (a>b) ifTrue: [nod value: (a-b) value: b].
    (a<b) ifTrue: [nod value: a value: (b-a)].
].

n := nod value: 1 value: 2.
n printNl.

It prints nil. And if I define with "early exit":

nod := [ :a :b |
    (a=b) ifTrue: [^a].
    (a>b) ifTrue: [nod value: (a-b) value: b].
    (a<b) ifTrue: [nod value: a value: (b-a)].
].

n := nod value: 1 value: 2.
n printNl.

It gives me the same error: return from a dead method context.

I solve this problem in this way:

nod := [ :a :b |
    (a=b) ifTrue: [
        a
    ] ifFalse: [
        (a>b) ifTrue: [nod value: (a-b) value: b] ifFalse: [nod value: a value: (b-a)].
    ]
].

n := nod value: 1 value: 2.
n printNl.

But I think, it is not beautiful way.

Solution

Drop the return statement (^) from your code and it will work fine.

In smalltalk, returning exits the method in which the return statement appears. It's used for early exits, for example a < b ifTrue: [^a] ifFalse:[^b].

In this case, you don't want the block to exit the containing method, you just want it to evaluate to something when sending it value:value:. A block evaluates to the last statement in it, so just make it a regular statement there and it will do the trick.

The error message you got, by the way, also explains the problem: you're trying to return 3 from a method which is already dead.