Show package:ghc-internal
The
Show class, and related operations.
Conversion of values to readable
Strings.
Derived instances of
Show have the following properties, which
are compatible with derived instances of
Read:
- The result of show is a syntactically correct Haskell
expression containing only constants, given the fixity declarations in
force at the point where the type is declared. It contains only the
constructor names defined in the data type, parentheses, and spaces.
When labelled constructor fields are used, braces, commas, field
names, and equal signs are also used.
- If the constructor is defined to be an infix operator, then
showsPrec will produce infix applications of the
constructor.
- the representation will be enclosed in parentheses if the
precedence of the top-level constructor in x is less than
d (associativity is ignored). Thus, if d is
0 then the result is never surrounded in parentheses; if
d is 11 it is always surrounded in parentheses,
unless it is an atomic expression.
- If the constructor is defined using record syntax, then
show will produce the record-syntax form, with the fields given
in the same order as the original declaration.
For example, given the declarations
infixr 5 :^:
data Tree a = Leaf a | Tree a :^: Tree a
the derived instance of
Show is equivalent to
instance (Show a) => Show (Tree a) where
showsPrec d (Leaf m) = showParen (d > app_prec) $
showString "Leaf " . showsPrec (app_prec+1) m
where app_prec = 10
showsPrec d (u :^: v) = showParen (d > up_prec) $
showsPrec (up_prec+1) u .
showString " :^: " .
showsPrec (up_prec+1) v
where up_prec = 5
Note that right-associativity of
:^: is ignored. For example,
- show (Leaf 1 :^: Leaf 2 :^: Leaf 3) produces the
string "Leaf 1 :^: (Leaf 2 :^: Leaf 3)".
Converting values to readable strings: the
Show class and
associated functions.
A specialised variant of
showsPrec, using precedence context
zero, and returning an ordinary
String.
The
shows functions return a function that prepends the
output
String to an existing
String. This allows
constant-time concatenation of results using function composition.
Pretty print the type. ShowType :: k -> ErrorMessage
Gets the string for a constructor
Show a type representation
Provides one possible concrete representation for
Version. For
a version with
versionBranch = [1,2,3] and
versionTags = ["tag1","tag2"], the output will be
1.2.3-tag1-tag2.
Get a string representation of the current execution stack state.
Render a stacktrace as a string
Show a signed
RealFloat value to full precision using standard
decimal notation for arguments whose absolute value lies between
0.1 and
9,999,999, and scientific notation
otherwise.
Show
non-negative Integral numbers in base 2.
Show a signed
RealFloat value using scientific (exponential)
notation (e.g.
2.45e2,
1.5e-3).
In the call
showEFloat digs val, if
digs is
Nothing, the value is shown to full precision; if
digs
is
Just d, then at most
d digits after the
decimal point are shown.
Show a signed
RealFloat value using standard decimal notation
(e.g.
245000,
0.0015).
In the call
showFFloat digs val, if
digs is
Nothing, the value is shown to full precision; if
digs
is
Just d, then at most
d digits after the
decimal point are shown.
Show a signed
RealFloat value using standard decimal notation
(e.g.
245000,
0.0015).
This behaves as
showFFloat, except that a decimal point is
always guaranteed, even if not needed.
Show a signed
RealFloat value using standard decimal notation
for arguments whose absolute value lies between
0.1 and
9,999,999, and scientific notation otherwise.
In the call
showGFloat digs val, if
digs is
Nothing, the value is shown to full precision; if
digs
is
Just d, then at most
d digits after the
decimal point are shown.
Show a signed
RealFloat value using standard decimal notation
for arguments whose absolute value lies between
0.1 and
9,999,999, and scientific notation otherwise.
This behaves as
showFFloat, except that a decimal point is
always guaranteed, even if not needed.
Show a floating-point value in the hexadecimal format, similar to the
%a specifier in C's printf.
>>> showHFloat (212.21 :: Double) ""
"0x1.a86b851eb851fp7"
>>> showHFloat (-12.76 :: Float) ""
"-0x1.9851ecp3"
>>> showHFloat (-0 :: Double) ""
"-0x0p+0"
Show
non-negative Integral numbers in base 16.
Show
non-negative Integral numbers in base 10.