Main data type

So-called Literals are one of:

• An unboxed (machine) literal (MachInt, MachFloat, etc.), which is presumed to be surrounded by appropriate constructors (Int#, etc.), so that the overall thing makes sense.
• The literal derived from the label mentioned in a "foreign label" declaration (MachLabel)

Creates a Literal of type Int#

Creates a Literal of type Word#

Creates a Literal of type Int64#

Creates a Literal of type Word64#

Creates a Literal of type Float#

Creates a Literal of type Double#

Creates a Literal of type Char#

Creates a Literal of type Addr#, which is appropriate for passing to e.g. some of the "error" functions in GHC.Err such as GHC.Err.runtimeError

Find the Haskell Type the literal occupies

True if code space does not go bad if we duplicate this literal Currently we treat it just like litIsTrivial

True if there is absolutely no penalty to duplicating the literal. False principally of strings.

"Why?", you say? I'm glad you asked. Well, for one duplicating strings would blow up code sizes. Not only this, it's also unsafe.

Consider a program that wants to traverse a string. One way it might do this is to first compute the Addr# pointing to the end of the string, and then, starting from the beginning, bump a pointer using eqAddr# to determine the end. For instance,

-- Given pointers to the start and end of a string, count how many zeros
-- the string contains.
countZeros :: Addr -> -> Int
countZeros start end = go start 0
  where
    go off n
      | off `addrEq#` end = n
      | otherwise         = go (off `plusAddr#` 1) n'
      where n' | isTrue off 0 0#) = n + 1
               | otherwise                                 = n

Consider what happens if we considered strings to be trivial (and therefore duplicable) and emitted a call like countZeros "hello" plusAddr# 5). The beginning and end pointers do not belong to the same string, meaning that an iteration like the above would blow up terribly. This is what happened in #12757.

Ultimately the solution here is to make primitive strings a bit more structured, ensuring that the compiler can't inline in ways that will break user code. One approach to this is described in #8472.

Tests whether the literal represents a zero of whatever type it is

Returns the Integer contained in the Literal, for when that makes sense, i.e. for Char, Int, Word and LitInteger.