Standard ML of New Jersey (SML/NJ)
SML/NJ is a popular implementation of the Standard ML programming language that was co-developed jointly by Bell Laboratories and Princeton University. It is released under a BSD like license.
References:
Questions tagged [smlnj]
866 questions
3
votes
1 answer
Pattern matching in SML - representing a list as (x::y)
I just started learning functional programming and I find myself very confused by the concept of pattern matching (i'm using SML). Take for example the following expression to insert an element in an ordered list:
fun insert (n,nil) = [n]
| insert…
macalaca
- 988
- 1
- 13
- 31
3
votes
3 answers
Confusing SML statement
I have this statement:
let val x =
let val x = 5
in(fn y =>(y,x+y))
end
in
let val y=3 and z=10
in x z
end
end;
The output is :
(10,15)
I've been trying to track how this answer was produced but am getting…
user2796815
- 465
- 2
- 11
- 18
3
votes
2 answers
SML map function
I have the function:
map(map(fn x =>[x])) [[],[1],[2,3,4]];
Which produces:
val it = [[],[[1]],[[2],[3],[4]]]
I don't understand how this function works. Doesn't each map function need both a function and a list? It seems that there isn't enough…
user2796815
- 465
- 2
- 11
- 18
3
votes
1 answer
How do I get an unhandled exception to be reported in SML/NJ?
I have the following SML program in a file named testexc.sml:
structure TestExc : sig
val main : (string * string list -> int)
end =
struct
exception OhNoes;
fun main(prog_name, args) = (
raise OhNoes
…
user3093557
- 51
- 3
3
votes
1 answer
Better display of boolean formulas
I want to implement a method for showing a propositional formula in SML. The solutions that I found so far was of this type:
fun show (Atom a) = a
| show (Neg p) = "(~ " ^ show p ^ ")"
| show (Conj(p,q)) = "(" ^ show p ^ " & " ^ show q ^ ")"
|…
TheAptKid
- 1,559
- 3
- 25
- 47
3
votes
4 answers
Filtering elements of one list by looking at boolean values from the second list
I have two lists of equal length. I want to filter the elements of the first list by looking, if the element, with the same index in the second list, has a true boolean value.
Example:
[1,2,3,4,5]:int list
[true,false,false,true,false]:bool…
TheAptKid
- 1,559
- 3
- 25
- 47
3
votes
1 answer
Does using closures in sml affect the speed of running code in the interactive compiler?
If I have a program say:
fun foo x =
let
fun bar y = y * y
in
x + (bar x)
end
foo 123;
When I run this program in SML/NJ without compiling, will it have to process the declaration of bar each
time foo is called? As it…
Henrik Sommerland
- 597
- 8
- 13
3
votes
2 answers
SML/NJ: How to use HashTable?
I really want to create a HashTable in SML, it seems there already is a structure for this in SML/NJ.
The question is, how do I use it? I've not fully understood how to use structures in SML, and some of the very basic examples in the book I read…
Horse SMith
- 1,003
- 2
- 12
- 25
3
votes
3 answers
How do I use the Queue library in SML/NJ
I see that the SML/NJ includes a queue structure. I can't figure out how to use it. How do I use the additional libraries provided by SML/NJ?
Joshua
- 26,234
- 22
- 77
- 106
3
votes
1 answer
Using folding procedures in sml
fun Dbt (nil,_) = nil
| Dbt (x::xs,y::ys) = (x::y)::(Dbt(xs,ys))
| Dbt (x::xs,nil) = [x]::(Dbt(xs,nil));
Is there a way of defining this function non-recursively by using higher order and or in built functions in sml??I have tried all I can…
Emma
- 323
- 3
- 16
3
votes
2 answers
Understanding sigs and structs with casting a built-in list type to a custom stack type
Suppose I have the beginning of the definition for a Stack like the following:
signature STACK = sig
type 'a stack
end;
structure Stack :> STACK = struct
type 'a stack = 'a list
end;
Clearly this doesn't work, because I can't cast a list to a…
AJcodez
- 31,780
- 20
- 84
- 118
3
votes
3 answers
SML/NJ - Pattern Matching an Dynamic Typing
Is it possible to write functions with dynamically typed input parameters?
I tried pattern matching, but apparently it does not work like this.
I wish to do something like this:
fun firstStr (0,n:string) = n
| firstStr (b:string,n:string) = if b>n…
Artium
- 5,147
- 8
- 39
- 60
3
votes
1 answer
Why do I have unexpected '#' in the output for this code?
I am trying to create a deriv function to differentiate
using a datatype as follows:
datatype Symex = RCOEFF of real
| COEFF of string
| VAR of string
| POWER of Symex * int
| NEG …
KVV
- 61
- 4
3
votes
2 answers
filtering values into two lists
So i'm new to sml and am trying to understand the ins/out out of it. Recently i tried creating a filter which takes two parameters: a function (that returns a boolean), and a list of values to run against the function. What the filter does is it…
theStig
- 612
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3
votes
2 answers
Signature inside of a structure
I want to place signature/structure pair inside a structure, like so:
structure Outer :> OUTER =
struct
signature INNER =
sig
...
end
structure Inner :> INNER =
struct
...
end
end
but even the simplest of…
Andrew Keeton
- 22,195
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- 72