X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=docs%2Fusers_guide%2Fghci.xml;h=579cf23208a1acb8b66f4198765c5a8d5d94a055;hb=f9f8667fd33c6963477327fd9c6b8ee52f7c040b;hp=86bfa8fc0c185e0e43caa379723b885966ef49b6;hpb=67b3443720b8dd58472cb92bc167adc97b935da4;p=ghc-hetmet.git
diff --git a/docs/users_guide/ghci.xml b/docs/users_guide/ghci.xml
index 86bfa8f..579cf23 100644
--- a/docs/users_guide/ghci.xml
+++ b/docs/users_guide/ghci.xml
@@ -929,6 +929,7 @@ right :: [a]
left:
+[qsort.hs:2:15-46] *Main> :set -fprint-evld-with-show
[qsort.hs:2:15-46] *Main> :print left
left = (_t1::[a])
@@ -948,6 +949,13 @@ left = (_t1::[a])
underscore, in this case
_t1.
+ The flag -fprint-evld-with-show instructs
+ :print to reuse
+ available Show instances when possible. This happens
+ only when the contents of the variable being inspected
+ are completely evaluated.
+
+
If we aren't concerned about preserving the evaluatedness of a
variable, we can use :force instead of
:print. The :force command
@@ -1017,6 +1025,7 @@ right :: [a]
The execution continued at the point it previously stopped, and has
now stopped at the breakpoint for a second time.
+
Setting breakpoints
@@ -1106,10 +1115,14 @@ right :: [a]
Single-stepping is a great way to visualise the execution of your
program, and it is also a useful tool for identifying the source of a
- bug. The concept is simple: single-stepping enables all the
- breakpoints in the program and executes until the next breakpoint is
- reached, at which point you can single-step again, or continue
- normally. For example:
+ bug. GHCi offers two variants of stepping. Use
+ :step to enable all the
+ breakpoints in the program, and execute until the next breakpoint is
+ reached. Use :steplocal to limit the set
+ of enabled breakpoints to those in the current top level function.
+ Similarly, use :stepmodule to single step only on
+ breakpoints contained in the current module.
+ For example:
*Main> :step main
@@ -1118,10 +1131,11 @@ _result :: IO ()
The command :step
- expr begins the evaluation of
+ expr begins the evaluation of
expr in single-stepping mode. If
expr is ommitted, then it single-steps from
- the current breakpoint.
+ the current breakpoint. :stepover
+ works similarly.
The :list command is particularly useful when
single-stepping, to see where you currently are:
@@ -1330,9 +1344,13 @@ a :: a
:trace and :history to establish
the context. However, head is in a library and
we can't set a breakpoint on it directly. For this reason, GHCi
- provides the flag -fbreak-on-exception which causes
- the evaluator to stop when an exception is thrown, just as it does when
- a breakpoint is hit. This is only really useful in conjunction with
+ provides the flags -fbreak-on-exception which causes
+ the evaluator to stop when an exception is thrown, and
+ -fbreak-on-error, which works similarly but stops only on
+ uncaught exceptions. When stopping at an exception, GHCi will act
+ just as it does when a breakpoint is hit, with the deviation that it
+ will not show you any source code location. Due to this, these
+ commands are only really useful in conjunction with
:trace, in order to log the steps leading up to the
exception. For example:
@@ -1923,6 +1941,12 @@ Prelude> :. cmds.ghci
will be printed. If name has
been loaded from a source file, then GHCi will also display
the location of its definition in the source.
+ For types and classes, GHCi also summarises instances that
+ mention them. To avoid showing irrelevant information, an instance
+ is shown only if (a) its head mentions name,
+ and (b) all the other things mentioned in the instance
+ are in scope (either qualified or otherwise) as a result of
+ a :load or :module commands.