See also the
--print-libdir modes in Section 4.5, “Modes of operation”.
-v option makes GHC
verbose: it reports its version number
and shows (on stderr) exactly how it invokes each phase of
the compilation system. Moreover, it passes the
-v flag to most phases; each reports its
version number (and possibly some other information).
Please, oh please, use the
when reporting bugs! Knowing that you ran the right bits in
the right order is always the first thing we want to
To provide more control over the compiler's verbosity,
-v flag takes an optional numeric
-v on its own is
-v3, and the other levels
have the following meanings:
Disable all non-essential messages (this is the default).
Minimal verbosity: print one line per
compilation (this is the default when
--interactive is on).
Print the name of each compilation phase as it
is executed. (equivalent to
The same as
-v2, except that in
addition the full command line (if appropriate) for
each compilation phase is also printed.
The same as
-v3 except that the
intermediate program representation after each
compilation phase is also printed (excluding
preprocessed and C/assembly files).
These two flags control the way in which GHC displays types, in error messages and in GHCi.
-fprint-explicit-foralls makes GHC print explicit
quantification at the top level of a type; normally this is suppressed. For example, in GHCi:
ghci> let f x = x ghci> :t f f :: a -> a ghci> :set -fprint-explicit-foralls ghci> :t f f :: forall a. a -> a
However, regardless of the flag setting, the quantifiers are printed under these circumstances:
ghci> :t GHC.ST.runST GHC.ST.runST :: (forall s. GHC.ST.ST s a) -> a
If any of the quantified type variables has a kind that mentions a kind variable, e.g.
ghci> :i Data.Coerce.coerce coerce :: forall (k :: BOX) (a :: k) (b :: k). Coercible a b => a -> b -- Defined in GHC.Prim
-fprint-explicit-kinds makes GHC print kind arguments
in types, which are normally suppressed. This can be important when you are using kind polymorphism.
ghci> :set -XPolyKinds ghci> data T a = MkT ghci> :t MkT MkT :: forall (k :: BOX) (a :: k). T a ghci> :set -fprint-explicit-foralls ghci> :t MkT MkT :: forall (k :: BOX) (a :: k). T k a
Causes GHC to emit the full source span of the syntactic entity relating to an error message. Normally, GHC emits the source location of the start of the syntactic entity only.
test.hs:3:6: parse error on input `where'
test296.hs:3:6-10: parse error on input `where'
And multi-line spans are possible too:
test.hs:(5,4)-(6,7): Conflicting definitions for `a' Bound at: test.hs:5:4 test.hs:6:7 In the binding group for: a, b, a
Note that line numbers start counting at one, but column numbers start at zero. This choice was made to follow existing convention (i.e. this is how Emacs does it).
Set the minimum size of the heap to
This option is equivalent to
see Section 4.17.3, “RTS options to control the garbage collector”.
Prints a one-line summary of timing statistics for the
GHC run. This option is equivalent to
+RTS -tstderr, see Section 4.17.3, “RTS options to control the garbage collector”.