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Re: no empty (zero) string predicate in Elisp


From: Emanuel Berg
Subject: Re: no empty (zero) string predicate in Elisp
Date: Sun, 26 Apr 2015 20:39:09 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)

Rusi <address@hidden> writes:

> Rather befuddled here... Do you want or not want
> empty-string-p??

Of course I want it! That's why I wrote it myself and
then suggested it be included.

> Your first post said you've defined it and you want
> it not in ELPA but emacs. Now you are saying you
> want a binary -- presumably (== "" whatever).

No, I meant *unary* - I just wrote:

    "Pascal J. Bourguignon" <address@hidden>
    writes:

    > The only problem with that, is that a binary
    > operator has 2 arguments:
    >     
    >     (binop a b)
    >
    > therefore if you want a binary operator, you
    > want:
    >
    >     (string= s "")
    >
    > On the other hand, if you want only one
    > argument, then you want a unary operator:
    >
    >     (unary a)

    Indeed! You have to read what I think, not what
    I write...

    OK, let's try again: I want a *unary* function
    because this involves a *single* argument (sounds
    logical, right?) - the function's value only
    depends on a property of this single argument.

    In math notation:


                /  true       x = ""
        f(x) = 
                \  false        else


    The implementation one the other hand may contain
    everything else that is needed, including the ""
    for comparison (in this case and in that
    implementation).

    While the *implementation* can be optimized for
    speed, the *function* and its interface should be
    formulated for clarity and "building blockness" as
    to facilitate ease of combination with other
    functions...

    This is the building block, toolchain, bottom-up
    approach which is the opposite of the fancy game
    of "programming" by drawing super-ambitious UML
    and class diagrams - "if you don't do it, it won't
    work ultimately", which is wrong - that approach
    very often fails, and when it does, instead of
    simply replacing the failing link, the whole thing
    must be done again, maybe with some slightly
    modified approach, "new ideas", etc.

    > and when this unary operator returns a boolean,
    > you call it a predicate
    >
    >     (emptyp s)

    Cool. "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).

-- 
underground experts united
http://user.it.uu.se/~embe8573


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