The Glorious Glasgow Haskell Compilation System User's Guide ...

The Glorious Glasgow Haskell
Compilation System User’s Guide,
Version 6.10.4 33 / 224
:set [option...] Sets various options. See Section 2.8 for a list of available options and Section 4.17.10 for a list of GHCispecific
flags. The :set command by itself shows which options are currently set. It also lists the current dynamic flag
settings, with GHCi-specific flags listed separately.
:set args arg ...
:set editor cmd
:set prog prog
Sets the list of arguments which are returned when the program calls System.getArgs.
Sets the command used by :edit to cmd.
Sets the string to be returned when the program calls System.getProgName.
:set prompt prompt Sets the string to be used as the prompt in GHCi. Inside prompt, the sequence %s is replaced by the
names of the modules currently in scope, and %% is replaced by %.
:set stop [num] cmd Set a command to be executed when a breakpoint is hit, or a new item in the history is selected. The
most common use of :set stop is to display the source code at the current location, e.g. :set stop :list.
If a number is given before the command, then the commands are run when the specified breakpoint (only) is hit. This can
be quite useful: for example, :set stop 1 :continue effectively disables breakpoint 1, by running :continue
whenever it is hit (although GHCi will still emit a message to say the breakpoint was hit). What’s more, with cunning use
of :def and :cmd you can use :set stop to implement conditional breakpoints:
*Main> :def cond \expr -> return (":cmd if (" ++ expr ++ ") then return \"\" else
return \":continue\"")
*Main> :set stop 0 :cond (x < 3)
Ignoring breakpoints for a specified number of iterations is also possible using similar techniques.
:show bindings
:show breaks
Show the bindings made at the prompt and their types.
List the active breakpoints.
:show context List the active evaluations that are stopped at breakpoints.
:show modules Show the list of modules currently loaded.
:show packages
Show the currently active package flags, as well as the list of packages currently loaded.
:show languages Show the currently active language flags.
:show [args|prog|prompt|editor|stop]
Displays the specified setting (see :set).
:sprint Prints a value without forcing its evaluation. :sprint is similar to :print, with the difference that unevaluated
subterms are not bound to new variables, they are simply denoted by ‘_’.
:step [expr] Single-step from the last breakpoint. With an expression argument, begins evaluation of the expression with
a single-step.
:trace [expr] Evaluates the given expression (or from the last breakpoint if no expression is given), and additionally logs
the evaluation steps for later inspection using :history. See Section 2.5.5.
:type expression Infers and prints the type of expression, including explicit forall quantifiers for polymorphic types.
The monomorphism restriction is not applied to the expression during type inference.
:undef name
:unset option...
Undefines the user-defined command name (see :def above).
Unsets certain options. See Section 2.8 for a list of available options.
:! command... Executes the shell command command.
←↪
2.8 The :set command
The :set command sets two types of options: GHCi options, which begin with ‘+’, and “command-line” options, which begin
with ‘-’.
NOTE: at the moment, the :set command doesn’t support any kind of quoting in its arguments: quotes will not be removed
and cannot be used to group words together. For example, :set -DFOO=’BAR BAZ’ will not do what you expect.