> no, i have to create the string '[ :foo | foo bar]' on the fly. (because
i
> don't know bar). i need to create this block at *run time*.
> 
Sorry Dave, I didn't get the quotes in the first place. 
In this case, you are looking for a way to create a BlockContext like this:

b := BlockContext new.
b
 home: aContextPart
 startpc: position
 nargs: anInteger

Well, nargs shouldn't be a problem (1), startpc could probably be 1 as
well, but home...
When I try the following:

b := BlockContext new.
b
 home: (Display restoreAfter:[])
 startpc: 1
 nargs: 0
b value

my Squeak is unexpectedly terminated...
Hope this helps.

Reinier.