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
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Function with different argument types
I read about polymorphism in function and saw this example
fun len nil = 0
| len rest = 1 + len (tl rest)
All the other examples dealt with nil arg too.
I wanted to check the polymorphism concept on other types, like
fun func (a : int) : int =…
URL87
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getting expression doesn't match error
I am trying to implement a node delete function for a Binary Search Tree in SML/nj.
However I am getting a constraint error, that I don't understand why...
datatype 'a tree = Empty | Node of 'a * 'a tree * 'a tree;
datatype 'a stree = STree of ('a *…
omega
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SML/NJ - the "fun act(f,x) = f(x) ;" signature
Declare on the follow function -
fun act(f,x) = f(x);
Makes the signature -
val act = fn : ('a -> 'b) * 'a -> 'b
What does ('a -> 'b) * 'a -> 'b means ?
URL87
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1 answer
mutex/lock/semaphore in SML
Does SML have a mutex/lock/semaphore/etc library? I couldn't find one anywhere in the docs. I couldn't even find a multithreading library anywhere. Does it exist?
Peter
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How to pattern match nested lists?
In sml/nj, I want to create a function that takes a list of non-empty lists, and returns a list of the first elements of each of those non-empty lists.
fun get_first [] = []
| get_first x::xs = (hd x)::get_first xs;
get_first: ('a list) list -> 'a…
omega
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SML - Build a new list with the elements of the original list - Error: operator and operand don't agree [literal]
Given a list of numbers , I want to create a new list where the element at index i
is the sum of all the i-1 elements before .
For example :
[1,4,6,9] -> [1,5,11,20]
I've written the following code :
fun sum nil = 0
| sum [x]=x
|…
JAN
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Check Whether or Not An Input is a Fibonacci Number
fun isfib(a) =
findfib(a,1,1)
and
findfib(b,x,y) =
val z = x + y
if b <= 1 then true
else if z > b then false
else if z = b then true
else fib(b,y,z)
I'm placing an input into the program and recursively trying to find out if…
user1672578
0
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1 answer
Handling anonymous functions in SML datatypes
I have the following datatype and 3 examples of tests:
datatype 'a test = Test of ('a -> bool) * string;
val pos = Test (fn x => x > 0, "pos");
val even = Test (fn x => x mod 2 = 0, "even");
val small = Test (fn x => x < 100, "small");
I'm still…
user595334
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1 answer
How to pattern match a function?
H,
I am trying to do pattern matching, but the input to the function is a curried function, how can you pattern match something like that?
Can anyone show me some examples please?
omega
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2 answers
foldl operation in SML
I perform the following foldl operation
foldl (fn (acc,y) => if acc>y then acc else y+1) 0 [1,3]
So, I expect this to produce me an result of 4 but it produces an output of 3. What am I missing ?
My trace is something like this:
acc: 0 y: 1
acc:…
Sibi
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SML Case and pattern matching
I have the follwing function that is suppose to return the value of a card. I'm not sure why the case Num => Num is giving the following error:
Error: Types of rules don't agree, Earlier rules rank->int this rule
rank->int->rank
Why would…
Komal Waseem
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number_in_month exercise (How to return nothing instead of an empty list in SML)
I am doing a programming assignment with SML. One of the functions requires me to return a list of triple tuples of ints ( (int * int * int) list ) use to other lists. The function sorts through dates and months to see if any of them coincide, if…
Sloth
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What is wrong with my function
i have the following function that is supposed to return true if the passed argument is a reasonable date and false otherwise. the problem is that it is returning false even for obviously reasonable dates and i can't figure out what is wrong with…
guthik
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SML: List.nth() function does not works inside Let..in..end?
I am back again with a basic question.! ;)
I have learned some of the List functions. "List.nth" is one of them. When I use this function in SML command window, It is working fine. But when used inside Let..in..end; block , It is not working.
I…
InnovWelt
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4 answers
number_in_month exercise
I am fresh on SML and doing a homework by that. "Write a function number_in_month that takes a list of dates and a month (i.e., an int) and returns how many dates in the list are in the given month."
That's what I worked out and cannot see anything…
Xiong Xiong
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