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Projects are specified to omake with OMakefiles. The OMakefile has a format similar to a Makefile. An OMakefile has three main kinds of syntactic objects: variable definitions, function definitions, and rule definitions.
Variables are defined with the following syntax. The name is any sequence of alphanumeric
characters, underscore _, and hyphen -.
<name> = <value>
Values are defined as a sequence of literal characters and variable expansions. A variable
expansion has the form $(<name>), which represents the value of the <name>
variable in the current environment. Some examples are shown below.
CC = gcc CFLAGS = -Wall -g COMMAND = $(CC) $(CFLAGS) -O2
In this example, the value of the COMMAND variable is the string gcc -Wall -g -O2.
Unlike make(1), variable expansion is eager and functional (see also the section on Scoping). That is, variable values are expanded immediately and new variable definitions do not affect old ones. For example, suppose we extend the previous example with following variable definitions.
X = $(COMMAND) COMMAND = $(COMMAND) -O3 Y = $(COMMAND)
In this example, the value of the X variable is the string gcc -Wall -g -O2 as
before, and the value of the Y variable is gcc -Wall -g -O2 -O3.
Variables definitions may also use the += operator, which adds the new text to an existing definition. The following two definitions are equivalent.
# Add options to the CFLAGS variable CFLAGS = $(CFLAGS) -Wall -g # The following definition is equivalent CFLAGS += -Wall -g
Arrays can be defined by appending the [] sequence to the variable name and defining initial
values for the elements as separate lines. Whitespace is significant on each line. The following
code sequence prints c d e.
X[] =
a b
c d e
f
println($(nth 2, $(X)))
The following characters are special to omake: $():,=#\. To treat
any of these characters as normal text, they should be escaped with the backslash
character \.
DOLLAR = \$
Newlines may also be escaped with a backslash to concatenate several lines.
FILES = a.c\
b.c\
c.c
Note that the backslash is not an escape for any other character, so the following works as expected (that is, it preserves the backslashes in the string).
DOSTARGET = C:\WINDOWS\control.ini
An alternative mechanism for quoting special text is the use $"..." escapes. The number of
double-quotations is arbitrary. The outermost quotations are not included in the text.
A = $""String containing "quoted text" ""
B = $"""Multi-line
text.
The # character is not special"""
Functions are defined using the following syntax.
<name>(<params>) =
<indented-body>
The parameters are a comma-separated list of identifiers, and the body must be placed on a separate set of lines that are indented from the function definition itself. For example, the following text defines a function that concatenates its arguments, separating them with a colon.
ColonFun(a, b) =
return($(a):$(b))
The return expression can be used to return a value from the function. A return
statement is not required; if it is omitted, the returned value is the value of the last expression
in the body to be evaluated. NOTE: as of version 0.9.6, return is a control
operation, causing the function to immediately return. In the following example, when the argument
a is true, the function f immediately returns the value 1 without evaluating the print
statement.
f(a) =
if $(a)
return 1
println(The argument is false)
return 0
In many cases, you may wish to return a value from a section or code block without returning from
the function. In this case, you would use the value operator. In fact, the value
operator is not limited to functions, it can be used any place where a value is required. In the
following definition, the variable X is defined as 1 or 2, depending on the value of a,
then result is printed, and returned from the function.
f_value(a) =
X =
if $(a)
value 1
else
value 2
println(The value of X is $(X))
value $(X)
Functions are called using the GNU-make syntax, $(<name> <args)),
where <args> is a comma-separated list of values. For example,
in the following program, the variable X contains the
value foo:bar.
X = $(ColonFun foo, bar)
If the value of a function is not needed, the function may also be called using standard function call notation. For example, the following program prints the string “She says: Hello world”.
Printer(name) =
println($(name) says: Hello world)
Printer(She)
Comments begin with the # character and continue to the end of the line.
Files may be included with the include or open form. The included file must use
the same syntax as an OMakefile.
include $(Config_file)
The open operation is similar to an include, but the file is included at most once.
open Config
# Repeated opens are ignored, so this
# line has no effect.
open Config
If the file specified is not an absolute filenmame, both include and
open operations search for the file based on the
OMAKEPATH variable. In case of the open directive, the search is
performed at parse time, and the argument to open may not
contain any expressions.
Scopes in omake are defined by indentation level. When indentation is increased, such as in the body of a function, a new scope is introduced.
The section form can also be used to define a new scope. For example, the following code
prints the line X = 2, followed by the line X = 1.
X = 1
section
X = 2
println(X = $(X))
println(X = $(X))
This result may seem surprising–the variable definition within the
section is not visible outside the scope of the section.
The export form, which will be described in detail in
Section 5.3, can be used to circumvent this restriction by
exporting variable values from an inner scope. It must be the final
expression in a scope. For example, if we modify the previous example
by adding an export expression, the new value for the X
variable is retained, and the code prints the line X = 2 twice.
X = 1
section
X = 2
println(X = $(X))
export
println(X = $(X))
There are also cases where separate scoping is quite important. For example, each OMakefile is evaluated in its own scope. Since each part of a project may have its own configuration, it is important that variable definitions in one OMakefile do not affect the definitions in another.
To give another example, in some cases it is convenient to specify a
separate set of variables for different build targets. A frequent
idiom in this case is to use the section command to define a
separate scope.
section
CFLAGS += -g
%.c: %.y
$(YACC) $<
.SUBDIRS: foo
.SUBDIRS: bar baz
In this example, the -g option is added to the CFLAGS
variable by the foo subdirectory, but not by the bar and
baz directories. The implicit rules are scoped as well and in this
example, the newly added yacc rule will be inherited by the foo
subdirectory, but not by the bar and baz ones; furthermore
this implicit rule will not be in scope in the current directory.
Top level conditionals have the following form.
if <test>
<true-clause>
elseif <text>
<elseif-clause>
else
<else-clause>
The <test> expression is evaluated, and if it evaluates to a true value (see
Section 8.2 for more information on logical values, and Boolean functions), the code
for the <true-clause> is evaluated; otherwise the remaining clauses are evaluated. There may
be multiple elseif clauses; both the elseif and else clauses are optional.
Note that the clauses are indented, so they introduce new scopes.
When viewed as a predicate, a value corresponds to the Boolean false, if its string
representation is the empty string, or one of the strings false, no, nil,
undefined, or 0. All other values are true.
The following example illustrates a typical use of a conditional. The
OSTYPE variable is the current machine architecture.
# Common suffixes for files
if $(equal $(OSTYPE), Win32)
EXT_LIB = .lib
EXT_OBJ = .obj
EXT_ASM = .asm
EXE = .exe
export
elseif $(mem $(OSTYPE), Unix Cygwin)
EXT_LIB = .a
EXT_OBJ = .o
EXT_ASM = .s
EXE =
export
else
# Abort on other architectures
eprintln(OS type $(OSTYPE) is not recognized)
exit(1)
Pattern matching is performed with the switch and match forms.
switch <string>
case <pattern1>
<clause1>
case <pattern2>
<clause2>
...
default
<default-clause>
The number of cases is arbitrary.
The default clause is optional; however, if it is used it should
be the last clause in the pattern match.
For switch, the string is compared with the patterns literally.
switch $(HOST)
case mymachine
println(Building on mymachine)
default
println(Building on some other machine)
Patterns need not be constant strings. The following function tests
for a literal match against pattern1, and a match against
pattern2 with ## delimiters.
Switch2(s, pattern1, pattern2) =
switch $(s)
case $(pattern1)
println(Pattern1)
case $"##$(pattern2)##"
println(Pattern2)
default
println(Neither pattern matched)
For match the patterns are egrep(1)-style regular expressions.
The numeric variables $1, $2, ... can be used to retrieve values
that are matched by \(...\) expressions.
match $(NODENAME)@$(SYSNAME)@$(RELEASE)
case $"mymachine.*@\(.*\)@\(.*\)"
println(Compiling on mymachine; sysname $1 and release $2 are ignored)
case $".*@Linux@.*2\.4\.\(.*\)"
println(Compiling on a Linux 2.4 system; subrelease is $1)
default
eprintln(Machine configuration not implemented)
exit(1)
OMake is an object-oriented language. Generally speaking, an object is a value that contains fields
and methods. An object is defined with a . suffix for a variable. For example, the
following object might be used to specify a point (1, 5) on the two-dimensional plane.
Coord. =
x = 1
y = 5
print(message) =
println($"$(message): the point is ($(x), $(y)")
# Define X to be 5
X = $(Coord.x)
# This prints the string, "Hi: the point is (1, 5)"
Coord.print(Hi)
The fields x and y represent the coordinates of the point. The method print
prints out the position of the point.
We can also define classes. For example, suppose we wish to define a generic Point
class with some methods to create, move, and print a point. A class is really just an object with
a name, defined with the class directive.
Point. =
class Point
# Default values for the fields
x = 0
y = 0
# Create a new point from the coordinates
new(x, y) =
this.x = $(x)
this.y = $(y)
return $(this)
# Move the point to the right
move-right() =
x = $(add $(x), 1)
return $(this)
# Print the point
print() =
println($"The point is ($(x), $(y)")
p1 = $(Point.new 1, 5)
p2 = $(p1.move-right)
# Prints "The point is (1, 5)"
p1.print()
# Prints "The point is (2, 5)"
p2.print()
Note that the variable $(this) is used to refer to the current object. Also, classes and
objects are functional—the new and move-right methods return new objects. In
this example, the object p2 is a different object from p1, which retains the original
(1, 5) coordinates.
Classes and objects support inheritance (including multiple inheritance) with the extends
directive. The following definition of Point3D defines a point with x, y, and
z fields. The new object inherits all of the methods and fields of the parent classes/objects.
Z. =
z = 0
Point3D. =
extends $(Point)
extends $(Z)
class Point3D
print() =
println($"The 3D point is ($(x), $(y), $(z))")
# The "new" method was not redefined, so this
# defines a new point (1, 5, 0).
p = $(Point3D.new 1, 5)
Objects provide one way to manage the OMake namespace. There are also four special objects that are further used to control the namespace.
The private. section is used to define variables that are private to the current file/scope.
The values are not accessible outside the scope. Variables defined in a private. object can
be accessed only from within the section where they are defined.
Obj. =
private. =
X = 1
print() =
println(The value of X is: $(X))
# Prints:
# The private value of X is: 1
Obj.print()
# This is an error--X is private in Obj
y = $(Obj.X)
In addition, private definitions do not affect the global value of a variable.
# The public value of x is 1
x = 1
f() =
println(The public value of x is: $(x))
# This object uses a private value of x
Obj. =
private. =
x = 2
print() =
x = 3
println(The private value of x is: $(x))
f()
# Prints:
# The private value of x is: 3
# The public value of x is: 1
Obj.print()
Private variables have two additional properties.
export directive, unless they are
mentioned explicitly. private. =
FLAG = true
section
FLAG = false
export
# FLAG is still true
section
FLAG = false
export FLAG
# FLAG is now false
The protected. object is used to define fields that are local to an object. They can
be accessed as fields, but they are not passed dynamically to other functions. The purpose of a
protected variable is to prevent a variable definition within the object from affecting other parts
of the project.
X = 1
f() =
println(The public value of X is: $(X))
# Prints:
# The public value of X is: 2
section
X = 2
f()
# X is a protected field in the object
Obj. =
protected. =
X = 3
print() =
println(The protected value of X is: $(X))
f()
# Prints:
# The protected value of X is: 3
# The public value of X is: 1
Obj.print()
# This is legal, it defines Y as 3
Y = $(Obj.X)
In general, it is a good idea to define object variables as protected. The resulting code is more modular because variables in your object will not produce unexpected clashes with variables defined in other parts of the project.
The public. object is used to specify public dynamically-scoped variables. In the following
example, the public. object specifies that the value X = 4 is to be dynamically
scoped. Public variables are not defined as fields of an object.
X = 1
f() =
println(The public value of X is: $(X))
# Prints:
# The public value of X is: 2
section
X = 2
f()
Obj. =
protected. =
X = 3
print() =
println(The protected value of X is: $(X))
public. =
X = 4
f()
# Prints:
# The protected value of X is: 3
# The public value of X is: 4
Obj.print()
The static. object is used to specify values that are persistent across runs of OMake. They
are frequently used for configuring a project. Configuring a project can be expensive, so the
static. object ensure that the configuration is performed just once. In the following
(somewhat trivial) example, a static section is used to determine if the LATEX command is
available. The $(where latex) function returns the full pathname for latex, or
false if the command is not found.
static. =
LATEX_ENABLED = false
print(--- Determining if LaTeX is installed )
if $(where latex)
LATEX_ENABLED = true
export
if $(LATEX_ENABLED)
println($'(enabled)')
else
println($'(disabled)')
The OMake standard library provides a number of useful functions for
programming the static. tests, as described in
Chapter 13. Using the standard library, the above can
be rewritten as
open configure/Configure
static. =
LATEX_ENABLED = $(CheckProg latex)
As a matter of style, a static. section that is used for configuration should print what it
is doing using the ConfMsgChecking and
ConfMsgResult functions (of couse, most of helper functions in
the standard library would do that automatically).
The usual dot-notation can be used for private, protected, and public variables (but not static variables).
# Public definition of X
public.X = 1
# Private definition of X
private.X = 2
# Prints:
# The public value of X is: 1
# The private value of X is: 2
println(The public value of X is: $(public.X))
println(The private value of X is: $(private.X))
The scoping objects help provide a form of modularity. When you write a new file or program, explicit scoping declarations can be used to define an explicit interface for your code, and help avoid name clashes with other parts of the project. Variable definitions are public by default, but you can control this with private definitions.
# These variables are private to this file
private. =
FILES = foo1 foo2 foo3
SUFFIX = .o
OFILES = $(addsuffix $(SUFFIX), $(FILES))
# These variables are public
public. =
CFLAGS += -g
# Build the files with the -g option
$(OFILES):
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