Re: no empty (zero) string predicate in Elisp

[Marcin Borkowski]

On 2015-04-26, at 21:06, Emanuel Berg <embe8573@student.uu.se> wrote:

> Marcin Borkowski <mbork@mbork.pl> writes:
>
>>> "Predicate" is a word from the grammars of human
>>> languages, but I don't know its exact meaning,
>>> neither there or in programming languages (until
>>> now as for programming).
>>
>> AFAIK, "predicate" is a word from /logic/, and it
>> means (more or less) a function which consumes one
>> or more arguments of any type and gives back
>> a truth-value.
>
> Doesn't all functions in logic do that?

First of all: IANAL (here L = logician;-)).  But...

For starters, in propositional calculus (AFAIK, also in first-order
logic) there are no "functions" per se, since there are no /sets/.
Furthermore, in the logic systems usually used by us mathematicians
there are no /types/.  AFAIK, the analogue of "type mismatch" in these
systems is just a plain old "syntax error".

What you probably refer to is the fact that in these simple logic
systems both predicates and logical connectives "generate"
truth-values.  However, there are other possibilities; analogues of
"functions" in these systems are called "terms".

Best,

-- 
Marcin Borkowski
http://octd.wmi.amu.edu.pl/en/Marcin_Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University