I was using the Pow function of the BigInteger class in F# when my compiler told me :
This construct is deprecated. This member has been removed to ensure that this
type is binary compatible with the .NET 4.0 type System.Numerics.BigInteger
Fair enough I guess, but I didn't found a replacement immediately.
Is there one? Should we only use our own Pow functions? And (how) will it be replaced in NET4.0?
You can use the pown function
let result = pown 42I 42
pown works on any type that 'understands' multiplication and 'one'.
If you look at F# from the perspective of being based on OCaml, then the OCaml Num module has power_num. Since OCaml type num are arbitrary-precision rational numbers they can handle any size number, e.g. they are not limited by the CPU register because they can do the math symbolically. Also since num is defined as
type num =
| Int of int
| Big_int of Big_int.big_int
| Ratio of Ratio.ratio
they can handle very small numbers with out loss of precision because of the Ratio type.
Since F# does not have the num type, Jack created the FSharp.Compatibility.OCaml module which has num.fs and is available via NuGet.
So you can get all the precision you want using this, and the num functions can handle negative exponents.
Related
I am beginning to learn how to use units of measure in F# but I haven't found the answer to this simple question yet. How do you print the resultant units after a calculation. I know that FSI prints them so they should be available somehow.
For example:
[<Measure>] type m;;
[<Measure>] type s;;
let d = 10<m>;;
val d : int<m> = 10
let t = 2<s>;;
val t : int<s> = 2
I want to do something like this:
printfn "Results: %A %A" (d / t) (UOM (d / t));;
"Results: 5 m/s"
Thanks in advance
Unfortunately, this is not possible.
Units of measure exist only at compile time. When you compile the program, they will be ereased (because .NET doesn't have any way of representing units for types). This means that at the runtime, the result of your calculation will be just float. I don't think there is any way other than just writing units as string in your code...
There was a related question some time ago. It has some more details and also explains why you cannot get information about units using reflection.
Why can not use reflection in f#
I have a simple F# function cost receiving a single parameter amount which is used for some calculations. It is a float so I need to pass in something like cost 33.0 which in math is the same as cost 33. The compiler complaints about it, and I understand why, but I would like being able to call it like that, I tried to create another function named the same and used type annotation for both of them and I also get compiler warnings. Is there a way to do this like C# does?
There are two mechanisms in F# to achieve this, and both do not rely on implicit casts "like C#":
(A) Method overloading
type Sample =
static member cost (amount: float) =
amount |> calculations
static member cost (amount: int) =
(amount |> float) |> calculations
Sample.cost 10 // compiles OK
Sample.cost 10. // compiles OK
(B) Using inlining
let inline cost amount =
amount + amount
cost 10 // compiles OK
cost 10. // compiles OK
F# doesn't allow overloading of let-bound functions, but you can overload methods on classes like in C#.
Sometimes, you can change the model to work on a Discriminated Union instead of a set of overloaded primitives, but I don't think it would be particularly sensible to do just to be able to distinguish between floats and integers.
if you want to use an int at call site but have a float inside the function body ; why not simply cast it ?
let cost amount =
// cast amount from to float (reusing the name amount to shadow the first one)
let amount = float amount
// rest of your function
I'm learning compilers and creating a code generator for a simple language that deals with two types: characters and integers.
After the user input has been scanned by the scanner and then parsed by the parser, I get an AST representation of the input. I have made a code generation for an even simpler language which only processes expressions with integers, operators and variables.
However with this new language I sometimes get a subtree for a type declaration, like this:
(IS TYPE (x) (INT))
which says x is of type INT.
Should there be a case in my code generator which deals with these type declarations? Or is this simply for the semantic analyzer to type check, so I should just assume the types have been checked and ignore this part of the tree and simply assign the value for x?
Both situations are possible, you need to describe more about your language, to see if you really need to add that feature to your code generator, or skip it as unnecessary, and avoid extra work with this difficult and interesting topic of designing a programming language.
Is you "code generator" a program that recieves as an input code in a programming language (maybe small one) and outputs code in another programming language (maybe small one) ?
This tool is usually called a "translator".
Is you "code generator" a program that receive as an input a programming language and outputs assembler / bytecode like programming language ?
This tool is usually called a "compiler".
Note: "pile" is a synonym for "stack".
Usually an A.S.T., stores the type of an operation, or function call. Example, in c:
...
int a = 3;
int b = 5;
float c = (float)(a * b);
...
The last line, generates an A.S.T. similar to this, (skip A.S.T. for other lines):
..................................................................
..................................................................
......................+--------------+............................
......................| [root] |............................
......................| (no type) = |............................
......................+------+-------+............................
.............................|....................................
.................+-----------+------------+.......................
.................|........................|.......................
...........+-----+-----+....+-------------+-------------+.........
...........| (int) c |....| (float) (cast operation) |.........
...........+-----------+....+-------------+-------------+.........
..........................................|.......................
....................................+-----+-----+.................
....................................| (int) () |.................
....................................+-----+-----+.................
..........................................|.......................
....................................+-----+-----+.................
....................................| (int) * |.................
....................................+-----+-----+.................
..........................................|.......................
..............................+-----------+-----------+...........
..............................|.......................|...........
........................+-----+-----+...........+-----+-----+.....
........................| (int) a |...........| (float) b |.....
........................+-----------+...........+-----------+.....
..................................................................
..................................................................
Note that the "(float)" cast its like an operator or a function,
similar to your question.
Good Luck.
If this is a declaration
(IS TYPE (x) (INT))
then x should be laid out in memory. In the case of C and automatic variables, local auto variables are allocated on stack. To allocate needed size of stack you should know sizes of all local vars and sizes are from types.
If this variable is stored in a register, you should select a register of needed size (think about x86 with: AL, AX, EAX, RAX - the same register with different sizes), if your target has such.
Also, type is needed when there is an ambiguous operation in AST, which can operate on different data sizes (e.g. char, short, int - or 8-bit, 16-bit, 32-bit, etc). And for some assemblers, size of data is encoded into instruction itself; so codegen should remember sizes of variables.
Or, if the type of operation was not recorded in AST, the ADD:
(ADD (x) (y))
may mean both float and int additions (ADD or FADD instructions), so types of x and y are needed in codegen to select right variant.
I am beginning to learn how to use units of measure in F# but I haven't found the answer to this simple question yet. How do you print the resultant units after a calculation. I know that FSI prints them so they should be available somehow.
For example:
[<Measure>] type m;;
[<Measure>] type s;;
let d = 10<m>;;
val d : int<m> = 10
let t = 2<s>;;
val t : int<s> = 2
I want to do something like this:
printfn "Results: %A %A" (d / t) (UOM (d / t));;
"Results: 5 m/s"
Thanks in advance
Unfortunately, this is not possible.
Units of measure exist only at compile time. When you compile the program, they will be ereased (because .NET doesn't have any way of representing units for types). This means that at the runtime, the result of your calculation will be just float. I don't think there is any way other than just writing units as string in your code...
There was a related question some time ago. It has some more details and also explains why you cannot get information about units using reflection.
Why can not use reflection in f#
let myuint64 = 10uL
match myuint64 with
| -1 -> ()
| _ -> ()
How do I define the given -1 as a uint64 value?
> match 0UL-1UL with
- |System.UInt64.MaxValue -> "-1"
- |_ -> "???"
- ;;
val it : string = "-1"
Let me leave alone the fact that you can't really represent a negative value with a data type that can only store positive values (and zero of course).
If, on the other hand, you were storing it in a signed value, -1 would be stored as all bits set.
So basically, I will assume you want to find a way to represent -1 as a bit-wise value that will be compatible with -1 as a signed value.
The value would then be, in C# and C/C++ syntax, 0xffffffffffffffff. Exactly how to specify that in F# I don't know.
I don't know F# at all, but if it's anything like any other languages, a UInt64 can't be -1. Ever. UInt means unsigned integer, which means it can only represent positive values.
To expand on other answers:
When a type starts with a u it means unsigned. What signed/unsigned means is this:
Numbers are stored using a certain number of bits. In the case of int64 and uint64, 64 bits are used. If the number is signed, the 1st bit is not used as part of the number itself, only the other 63 are. That bit is used to say whether the number is negative. If the number is unsigned, then all bits including the 1st bit are used as part of the number and the number is always non-negative (ie: is positive or 0).
Well you could assign it -1 and on most architectures store the 2's complement in there. The signed and unsigned stuff are really only for the type checking. There is no negative sign in hardware.
I have no idea if f# type checker is smart enough to know that a lexical constant -1 is a negative number and should not be put in a uint64.
C definitely does not care.
#include <stdio.h>
#include <inttypes.h>
main()
{
uint64_t x = -1;
printf("0x%x\n", x); // 0xffffffff
}
if F# will convert it for you then -1UL would work. If not then you can specify it as 0xFFFFFFFFFFFFFFFFUL and add a comment to remember that it's -1.
Don't have the F# tools installed at the moment so I cannot verify this.
If you want to go with a signed int:
-1: int64
but you can't match a negative number to a uint, as others have stated.