Literals in Programming Languages(gavilan.edu)

38 pointsby RohitS5vor 13 Jahren22 comments

http://www.gavilan.edu/csis/languages/literals.html

4 comments

jmmcdvor 13 Jahren

This article is only about primitive literals, not compound ones. I think the list and dict literals in Python are the #1 reason I like it better than C. I think the regexp literals in Perl were one of the main reasons people liked Perl better than C.

mahmudvor 13 Jahren

That line blurs when you have homoiconic syntax, specially one with a programmable reader. Common Lisp uses the # for dispatch macro character, you can define your own literals, in whatever environment you want.

http://www.franz.com/support/documentation/6.2/ansicl/subsec...

arethuzavor 13 Jahren

Can't you set any dispatch character you like using make-dispatch-macro-character ?

mahmudvor 13 Jahren

Oh yes, you can set your own dispatch characters, but the # is the dispatch character for the CL standard syntax.

DerekLvor 13 Jahren

C99 has array and struct literals:

  (int []) { 1, 2, 3 }
  (struct Point) { 3, 5 }
  (struct Point) { .x = 3, .y = 5 }

masklinnvor 13 Jahren

> This article is only about primitive literals, not compound ones.

It mentions array literals: http://www.gavilan.edu/csis/languages/literals.html#_Toc7587...

pilgrim689vor 13 Jahren

> I like [Python] better than C

Isn't it strange to compare Python/Perl to C and say that one is better than the other? It's apples to oranges. You wouldn't use Python or Perl to build an OS, and you wouldn't use C to prototype a web app.

jmmcdvor 13 Jahren

Sure, but I said "like", not "better". When I learned Python, I had that feeling described as weightlessness by xkcd [http://xkcd.com/353/], because I didn't have to write several lines and a loop to make a list. It made me happy. Fair comparisons don't really come into it.

tantalorvor 13 Jahren

> Booleans are ordinal values and usually false is less than true.

I was surprised to find this is true,

http://plato.stanford.edu/entries/truth-values/#3

jonsenvor 13 Jahren

So in fact you believed it was false before true then ;-)

ibottyvor 13 Jahren

well i believed that they are not ordered. (which they are not in some languages)

tantalorvor 13 Jahren

That's what I thought, but it appears truth values are typically defined with a partial ordering a <= b iff a && b == a, which gives false <= false < true <= true.

You could choose to ignore that partial ordering at your own peril.

cpetersovor 13 Jahren

In Visual Basic, False is 0 and True is -1.

etermvor 13 Jahren

-1 == 1 (mod 2) [But yes, this is Yet Another Reason vb can be irritating to the seasoned programmer.]

saurikvor 13 Jahren

(I always found VB's definition more obvious, given that -1 == ~0.)

ubernostrumvor 13 Jahren

In Python, bool is a subclass of int. The constants True and False have the values 1 and 0 respectively, and it's legal to do arithmetic with them :)

swahvor 13 Jahren

Factor has them for many data-structures: http://docs.factorcode.org/content/article-syntax-literals.h..., but they are simple to add in a concatenative language

(they might as well have been added by a user library).

anders0vor 13 Jahren

To nitpick, -14 isn't a literal in all languages. :)

(In Haskell, it's just sugar for negate 14, while in Standard ML it's spelt ~14. And I assume there are other exceptions too.)

pdwvor 13 Jahren

Even in C it's not a literal. The consequence is that in a 32-bit implementation, you can't write INT_MIN as -2147483648 (-2^31), because 2147483648 would overflow a signed int. Instead a workaround such as -2147483647-1 must be used.

shaurzvor 13 Jahren

Making the minus part of the literal can lead to parsing ambiguity. For example, "x-3" would parse as 2 tokens "x" and "-3" (instead of 3 tokens "x", "-" and "3") which would be a syntax error in C. The only workaround I can think of is making any expression followed by a negative number parse as a subtraction.

reycharlesvor 13 Jahren

> Making the minus part of the literal can lead to parsing ambiguity.

Not really. It's done in java. Usually, minus ("-") is parsed as a token and then unary minus on integer literals are transformed to a negative integer literal.

So, -2147483648 is read as MINUS INT_LITERAL and thus transformed into "-2147483648" as an INT_LITERAL, but -(2147483648) should be read as MINUS L_PAREN INT_LITERAL R_PAREN and should thus not be transformed.

anders0vor 13 Jahren

Huh. I always assumed it was in C. Shows what I know… :p