:: String -> Int -package:hledger-lib -package:speculate -package:polysemy -package:ghc-boot -package:string-conversions -package:hxt

Raises an error with a printf-specific prefix on the message string.
Deprecated: error appends the call stack now
Panics and asserts.
Panics and asserts.
Panics and asserts.
Coerce a value from one type to another, bypassing the type-checker. There are several legitimate ways to use unsafeCoerce:
  1. To coerce e.g. Int to HValue, put it in a list of HValue, and then later coerce it back to Int before using it.
  2. To produce e.g. (a+b) :~: (b+a) from unsafeCoerce Refl. Here the two sides really are the same type -- so nothing unsafe is happening -- but GHC is not clever enough to see it.
  3. In Data.Typeable we have
eqTypeRep :: forall k1 k2 (a :: k1) (b :: k2).
TypeRep a -> TypeRep b -> Maybe (a :~~: b)
eqTypeRep a b
| sameTypeRep a b = Just (unsafeCoerce HRefl)
| otherwise       = Nothing

Here again, the unsafeCoerce HRefl is safe, because the two types really are the same -- but the proof of that relies on the complex, trusted implementation of Typeable.
  1. The "reflection trick", which takes advantage of the fact that in class C a where { op :: ty }, we can safely coerce between C a and ty (which have different kinds!) because it's really just a newtype. Note: there is no guarantee, at all that this behavior will be supported into perpetuity.
Highly, terribly dangerous coercion from one representation type to another. Misuse of this function can invite the garbage collector to trounce upon your data and then laugh in your face. You don't want this function. Really.
The function unsafeCoerce# allows you to side-step the typechecker entirely. That is, it allows you to coerce any type into any other type. If you use this function, you had better get it right, otherwise segmentation faults await. It is generally used when you want to write a program that you know is well-typed, but where Haskell's type system is not expressive enough to prove that it is well typed. The following uses of unsafeCoerce# are supposed to work (i.e. not lead to spurious compile-time or run-time crashes):
  • Casting any lifted type to Any
  • Casting Any back to the real type
  • Casting an unboxed type to another unboxed type of the same size. (Casting between floating-point and integral types does not work. See the GHC.Float module for functions to do work.)
  • Casting between two types that have the same runtime representation. One case is when the two types differ only in "phantom" type parameters, for example Ptr Int to Ptr Float, or [Int] to [Float] when the list is known to be empty. Also, a newtype of a type T has the same representation at runtime as T.
Other uses of unsafeCoerce# are undefined. In particular, you should not use unsafeCoerce# to cast a T to an algebraic data type D, unless T is also an algebraic data type. For example, do not cast Int->Int to Bool, even if you later cast that Bool back to Int->Int before applying it. The reasons have to do with GHC's internal representation details (for the cognoscenti, data values can be entered but function closures cannot). If you want a safe type to cast things to, use Any, which is not an algebraic data type. Warning: this can fail with an unchecked exception.
Warning: this can fail with an unchecked exception.
Warning: this can fail with an unchecked exception.
Convert to an Int. It is implementation-dependent what fromEnum returns when applied to a value that is too large to fit in an Int.
a constant function, returning the number of digits of floatRadix in the significand
exponent corresponds to the second component of decodeFloat. exponent 0 = 0 and for finite nonzero x, exponent x = snd (decodeFloat x) + floatDigits x. If x is a finite floating-point number, it is equal in value to significand x * b ^^ exponent x, where b is the floating-point radix. The behaviour is unspecified on infinite or NaN values.
The read function reads input from a string, which must be completely consumed by the input process. read fails with an error if the parse is unsuccessful, and it is therefore discouraged from being used in real applications. Use readMaybe or readEither for safe alternatives.
>>> read "123" :: Int
>>> read "hello" :: Int
*** Exception: Prelude.read: no parse
Deprecated: Use bitSizeMaybe or finiteBitSize instead
Return the number of set bits in the argument. This number is known as the population count or the Hamming weight. Can be implemented using popCountDefault if a is also an instance of Num.