smlnj

问题 I'm using SML/NJ, and I need to use a set of functions that are in a certain file f1.sml inside another file f2.sml . However, I'm not running f2.sml directly, rather, I'm importing it from somewhere else. If I use the use command in f2.sml with the path to f1.sml relative to f2.sml perspective, by the time I import f2.sml , it will look for the supplied path from the running script perspective. I cannot use absolute paths, and I'd like not to merge the two files contents. Sorry if this is a

问题 For instance: vagrant@precise32:/vagrant$ rlwrap sml Standard ML of New Jersey v110.76 [built: Mon May 12 17:11:57 2014] - TextIO.StreamIO.inputLine ; [autoloading] [library $SMLNJ-BASIS/basis.cm is stable] [autoloading done] val it = fn : ?.TextIO.instream -> (string * ?.TextIO.instream) option - val s = TextIO.openIn "README.md" ; val s = - : TextIO.instream - TextIO.StreamIO.inputLine s ; stdIn:3.1-3.28 Error: operator and operand don't agree [tycon mismatch] operator domain: ?.TextIO

问题 Consider the following SML function: fn x => x x This produces the following error (Standard ML of New Jersey v110.72): stdIn:1.9-1.12 Error: operator is not a function [circularity] operator: 'Z in expression: x x I can sort of see why this isn't allowed -- for one, I'm not really sure how to write down what its type would be -- but it's not completely nonsensical; for instance, I could pass the identity function to it and get it back. Is there a name for this function? (Is there a way to

问题 I am just starting to learn SML and having issues. I want to define a datatype, for a list that is not homogeneous. Take for example val a = [1,[2,4,3],5,[2,6]] I have made this datatype datatype 'a MulList = List of 'a multiList list | E of 'a; but I get the following error /tmp/emacs-region29207RwC:8.34-8.43 Error: unbound type constructor: multiList uncaught exception Error raised at: ../compiler/TopLevel/interact/evalloop.sml:66.19-66.27 ../compiler/TopLevel/interact/evalloop.sml:44.55 ..

问题 everyone, what is difference between the following assignments in ML, val n = 5; and n := 1; 回答1: The former is a declaration of a new, immutable variable. The latter is how you re-assign the value of a reference cell. 来源： https://stackoverflow.com/questions/5168889/ml-assignment-operation

问题 Please help I have no idea how what a string option does. is it possible to convert string option to a string? 回答1: As already pointed out you could use pattern matching to get the desired result. So, something like this: fun foo(NONE) = "" | foo(SOME a) = a; But you could spare the trouble and use Option.valOf function from SML library instead by just doing: Option.valOf(SOME "my string"); (Or just valOf(SOME "my string"); as newacct pointed out in the comments.) 回答2: The "option" type in ML

问题 I'm new to Standard ML and I'm trying to get my head around the SML/NJ runtime environment. I want to adapt it to my needs. Specifically, I want to: Use IntInf by default Prevent it from truncating strings and IntInf to 70 characters. Here's what I've found in my 8+ hours reading documentation and experimenting. I can overload IntInf on top of int with the command open IntInf; I can control how many characters in a string are displayed with the variable Control.Print.stringDepth. For example,

问题 I have read a lot about continuations and a very common definition I saw is, it returns the control state. I am taking a functional programming course taught in SML. Our professor defined continuations to be: "What keeps track of what we still have to do" ; "Gives us control of the call stack" A lot of his examples revolve around trees. Before this chapter, we did tail recursion. I understand that tail recursion lets go of the stack to hold the recursively called functions by having an

问题 Basically, I want to have a function to return a polymorphic function, some thing like this: fun foo () = fn x => x So the foo function takes in a value of type unit and returns a polymorphic identity function and the compiler is happy with that, it gives me: val foo = fn : unit -> 'a -> 'a but once I actually call the foo function, the return value is not what I expected val it = fn : ?.X1 -> ?.X2 Can't generalize because of value restriction it says, any help? thanks in advance 回答1: For

问题 How do I go about passing command-line arguments to an SML script? I'm aware that there is a CommandLine.arguments() function of the right type ( unit -> string list ), but invoking the interpreter like so: $ sml script_name.sml an_argument another_one doesn't give me anything. Pointers? 回答1: Try this. (* arg.sml *) val args = CommandLine.arguments() fun sum l = foldr op+ 0 (map (valOf o Int.fromString) l) val _ = print ("size: " ^ Int.toString (length args) ^ "\n") val _ = print ("sum: " ^