With all this discussion of tacit modifiers, I fear their lower-order
cousins are going out of style!
The proof of completeness for trains
(https://code.jsoftware.com/wiki/Essays/Trains#Proof_of_Completeness)
contains two concerning notes:
Without loss of generality, assume that [sentence] s contains no
copulae; for if it does, d=.rhs (say), recursively replace instances of
d by (rhs)
This transformation is problematic if rhs performs side effects; for it
may cause those effects to be performed more than once, or not at all; or
to be sequenced differently relatively to other side effects.
In some cases, it may nevertheless possible to straightforwardly express
an effectful verb tacitly. For instance:
{{ a=. 0 [ echo y
a + y + a }}
becomes:
(] + [ + ]) (0 [ echo)
but some are not so straightforward
{{ a=. 0 [ echo y
b=. 0 [ echo y
a + b + y + a + b }}
It can be done, of course, but not without cheating (e.g. by using boxes,
or by observing that + is commutative).
Question: what is a clear and concise definition of the subset of
effectful explicit verbs which may be made tacit without cheating?
Suppose s is a sentence [that] makes no use of x. or y. as arguments to
an adverb or conjunction
A shame; on multiple occasions, I have wanted to do exactly this, and have
had to write explicit code. (In some cases, it is possible to get around
the problem by passing a gerund to the conjunction; but that is not
general; it is somewhat obscure; and frequently requires redundant [ or ].)
Suggestion: a new primitive adverb. Call it 'n.'. Like [:, it is
syntactically regular, but semantically irregular. Just as there is a
rule for the evaluation of forks whose left tines are [: which takes
precedence over the regular rule for the evaluation of forks, so are there
rules for the evaluation of sentences containing n. which take precedence
over the rules for evaluation of ordinary sentences:
[x] u C (v n.) y
[x] u C ([x] v y) y
[x] u n. C v y
[x] ([x] u y) C v y
[x] u n. A y
[x] ([x] u y) A y
Objections:
- n. assumes that modifiers return verbs. Something like 'u n. A'
_must_ be assumed to be a verb for this mechanism to make any sense.
Evaluation of A must be deferred, which is even more irregular than [:.
- The common case of u C (f y) requires many parentheses if the input is
modified by a train: u C ((f g h)n.). (On the other hand, this is no
worse than the explicit code, which must write u C ((f g h) y).
NARS2000 suggests a mitigation in the form of higher-order modifiers:
assuming a higher-order ~, one might write (f g h)n. ~C u. This is not
a serious suggestion.)
-E
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