.\" @(#)mkhprog.1	2.3 dated 92/06/23 at 15:02:17
.TH MKHPROG 1 local
.SH NAME
mkhprog \- make skeleton of a Haskell program
.SH SYNOPSIS
.B mkhprog
[
.B \-l
] [
.B \-m
module_name ] [
.B \-o
file_name ] [[\-flag type] ... ]
.SH DESCRIPTION
.I mkhprog
will make the skeleton of a Haskell program, which includes the code for
parsing command line arguments
that almost all programs need.
.PP
The program so made is normally written to the standard output.
It can be placed in a named file by using the
.B \-o
flag, see below.
To get a feel for the generated code, give the command:
.IP
mkhprog \-o Main.hs \-b Bool \-s String \-n Int
.PP
and look at the program produced in
.IR Main.hs .
.PP
Flags following any
.BR \-l ,
.B \-m
or
.B \-o
options are those to be interpreted by the generated program.
Each such flag must be followed by a Haskell type, which is the type of
the value associated with that flag by the generated program.
Thus
.IP
mkhprog \-b Bool \-s String \-n Int \-f Foo
.PP
produces a program which interprets a binary flag,
.IR b ,
a flag followed by a string argument,
.IR s ,
a flag followed by an
.I Int
argument,
.IR n ,
and a flag followed by an argument of type
.IR "Foo, f" .
That program would be invoked, for example, as
.IP
prog \-b \-n 17 \-s string \-f "MkFoo 3 True"
.PP
assuming
.I MkFoo 3 True
is a valid item of type
.IR Foo .
.PP
A special form of binary flag is available by using
.I +flag Bool
instead of
.I "\-flag Bool" :
this produces a program which interprets
.I \-flag
to set an internal value to
.IR False ,
and
.I +flag
to set an internal value to
.IR True .
.PP
Internally, the values of the flags, plus their command line
arguments, are passed to a function which can process them as it wishes.
.PP
Such values are initialized explicitly to the empty string in the case of
.IR String s ,
and
.I False
in the case of
.IR Bool s .
The user must declare the default value for other types.
.PP
The flags interpreted by
.I mkhprog
are:
.TP
.B \-l
produce a ``literate'' Haskell program, in which lines of code begin with
``> ''.
.TP
.BI \-m " module_name"
Produces a module called
.I module_name
rather than the default
.IR Main .
.TP
.BI \-o " file_name"
Writes the generated program to
.I file_name
rather than the standard output.
.SH POINTS TO NOTE
.I mkhprog
uses the Haskell function
.I reads
to read values other than
.IR String s
and
.IR Bool s .
Thus, while flags with type
.I String
do not need quotes round their argument, any other sorts of
.I String
will need quotes.
For example, if
.I Bar
is a type synonym for
.IR String ,
then a program generated with
.IP
mkhprog \-f Bar
.PP
will have to be invoked as
.IP
prog \-f \\"string\\"
.PP
Some Haskell compilers produce programs whose command line parameters are
not all available to a call of
.IR getArgs .
For example,
.I getArgs
may only pick up arguments following an isolated \-.
Check your documentation for details.
.PP
Because
.I mkhprog
interprets the
.BR \-l ,
.B \-m
and
.B \-o
flags, it can be difficult to generate a program which itself interprets them.
The easiest solution to this is to use a flag name which
.I mkhprog
does not interpret and then change its name in the generated program.
.SH ACKNOWLEDGEMENTS
The functionality and manual page of
.I mkhprog
are based on those of the C program
.IR mkprog ,
though the implementation is entirely different.