Questions tagged [special-form]
15 questions
15
votes
7 answers
can if be a proper function rather than a special form
I finally started learning functional languages (emacs lisp) and it makes explicit distinction between functions and special forms such as flow control , for example if.
Is there a fundamental/theoretical reason why special forms are distinct from…
Anycorn
- 50,217
- 42
- 167
- 261
8
votes
1 answer
Is there a way to get a collection of clojure special forms programatically?
Does something similar to this exist?:
(deftest fantasy
(is (= ["let" "def" "ns" "etc."] clojure.core/special-chars)))
Nick Orton
- 3,563
- 2
- 21
- 28
6
votes
1 answer
Why is do a special form?
In Clojure, why is do a special form, instead of a function implemented like this?
(defn do [& exprs]
(last exprs))
Sam Estep
- 12,974
- 2
- 37
- 75
5
votes
2 answers
Scheme/Racket: Fold with booleans
(foldr + 0 '(1 2 3 4))
returns 10 which is what I expect, but
(foldr and false '(true true false))
gives me the error
and: expected an open parenthesis before and, but found none
foldr takes a function (which takes two parameters, since I have…
newprogrammer
- 2,514
- 2
- 28
- 46
3
votes
5 answers
How is "+" Implemented in Common Lisp Using Special Operators/Forms
In On Lisp (page 9), one can find the following claim:
Functions are the building-blocks of Lisp programs. They are also the building-blocks of Lisp. In most languages the + operator is something quite different
from user-defined functions. But…
MadPhysicist
- 5,401
- 11
- 42
- 107
3
votes
2 answers
What does the 'do' special form do?
Documentation says:
(do exprs*)
Evaluates the expressions in order and returns the value of the last. If no expressions are supplied, returns nil.
However, I just did this:
(defn blah []
(print "how")
(print "now")
(print "brown")
…
user1992634
- 764
- 7
- 16
2
votes
3 answers
Clojure asterisks special forms (fn*, let*, etc...)
I discovered that a lot of "special forms" are just macros that use their asterisks version in the background (fn*, let* and all the others).
In case of fn, for example, it adds the destructuring capability into the mix which fn* alone does not…
Lazarus535
- 1,158
- 1
- 8
- 23
2
votes
1 answer
Dynamic symbols in Clojure Macro/Special Form
I have a question regarding how to define functions/macros which call other macros or special forms but where one of the symbols passed in needs to be dynamic.
The simplest version of this question is described below:
We can define variables using…
WuHoUnited
- 8,279
- 3
- 24
- 27
1
vote
3 answers
Is the "else" keyword, used as final case in a cond-expression, a special form in Scheme?
The cond-expression in Scheme is a special form, but is the else keyword, used as final case in a cond-expression, a special form? Or is it just a reserved keyword that is essentially equivalent to the truth-value #t ?
In the latter case, why cannot…
Kim Mens
- 325
- 1
- 13
1
vote
1 answer
Elixir macros, quoting bitstring patternmatch types
I am working on a project in which I am likely to be writing a lot of code of the form:
defmodule Kind
defstruct [name1, name2, name3]
@type t :: %Kind{name1: integer(), name2: integer(), name3: binary()}
def unpack(input) do
with…
Vivian
- 1,539
- 14
- 38
1
vote
2 answers
Renaming Clojure's special forms
What's the best way to rename Clojure's special forms?
For example, if I preferred defvar over def or defun over defn, what would be the best way to go about it?
Selam S
- 43
- 3
1
vote
2 answers
Scheme evaluating procedures and special forms
I have a question on the evaluation of Scheme, I just want to make sure I have a correct understanding on how procedures are evaluated.
So when the Scheme interpreter starts to evaluate a list, the first element is evaluated, this has to evaluate to…
Kieran Maguire
- 35
- 4
1
vote
2 answers
What would the consequences be of allowing special forms to be treated as normal values?
I discovered that special forms can not be passed as arguments or saved in variables, both in Clojure:
user=> (defn my-func
[op]
(op 1 2 3))
#'user/my-func
user=> (my-func +)
6
user=> (my-func if)
java.lang.Exception: Unable to…
Matt Fenwick
- 48,199
- 22
- 128
- 192
0
votes
1 answer
How to use “and” with “seq-reduce” in Elisp?
I’m trying to write something like this:
(setq l '(nil t nil nil))
(seq-reduce 'and l t)
I get this error:
Invalid function: and
My understanding, after a bit of googling, is that this is due to and being a special form.
What would be a good way…
Philippe-André Lorin
- 994
- 7
- 25
-1
votes
2 answers
Primitive procedures and special forms in Scheme
In Scheme, are primitive procedures considered special forms?
Also, a bit too general but how is define different from other special forms?
Tomer
- 231
- 2
- 3
- 8