Brian Schott asked:
> Is the following behavior predictable
> from the Dictionary?
Yes. The fundamental rule to keep in mind is the shapes of arguments to the
dyad must share a common prefix with respect to the
rank of that dyad. The dyad + has ranks 0 0 so its frames include the
entire shapes of its arguments. Hence, the shape of
one of its arguments must be a (possibly total) prefix of the shape of the
other.
In your example cases:
NB. Brian's example arguments
a=: '' ; 1
a=: a,: '' ;~ 1
a=: a, '' ; ''
a=: a, 1 ; i.0
a=: a, 1 ; i.0 0
a=: a, 1 2;i.0 0
a=: a, '' ;1 2
a=: a, 10 ;1 2
NB. Display of examples attempted
egs =: 4 : ' ''('',(5!:5<''x''),'') + '',5!:5<''y'' '&.>/"1
NB. Display whether the attempted addition
NB. succeeded or failed.
add =: 'ok'"_@:+ :: ('err'"_)&.>/"1
NB. Determines whether shapes share a common prefix
NB. wrt rank of + (i.e. 0 0 0 )
pfx =: [: ([: -:&.>/ <.&#&>/ {.&.> ])"1 $&.>
NB. Correspondence: 3 columns
NB. 0. example sentence
NB. 1. result (ok or err)
NB. 2. do arguments share a prefix?
cor =: egs ,. add ,. pfx
cor a
+-------------+---+-+
|('') + 1 |ok |1|
+-------------+---+-+
|(1) + '' |ok |1|
+-------------+---+-+
|('') + '' |ok |1|
+-------------+---+-+
|(1) + i.0 |ok |1|
+-------------+---+-+
|(1) + i.0 0 |ok |1|
+-------------+---+-+
|(1 2) + i.0 0|err|0|
+-------------+---+-+
|('') + 1 2 |err|0|
+-------------+---+-+
|(10) + 1 2 |ok |1|
+-------------+---+-+
-Dan
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