OMAKE-LANGUAGE(1)

NAME
omake is a flexible build system designed for building a wide variety of projects. This document describes the language concepts and syntax. For an overview of omake, see the omake(1) man page.

OMAKE CONCEPTS AND SYNTAX

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

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.

  ADDING TO A VARIABLE DEFINITION

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

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)))

  SPECIAL CHARACTERS AND QUOTING

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"""

  FUNCTION DEFINITIONS

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

Comments begin with the # character and continue to the end of the line.

  FILE INCLUSION

Files may be included with the include form. The included file must use the same syntax as an OMakefile.

    include files.omake

  SCOPING, SECTIONS

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 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.

  CONDITIONALS

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 the Logic section), 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.

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)

  MATCHING

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)

OBJECTS

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.

  CLASSES

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.

  INHERITANCE

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)

SPECIAL OBJECTS/SECTIONS

Objects provide one way to manage the OMake namespace. There are also four special objects that are further used to control the namespace.

  PRIVATE.

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.

1.  Private variables are local to the file in which they are defined.

2.  Private variables are not exported by the 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

  PROTECTED.

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.

  PUBLIC.

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()

  STATIC.

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)')

As a matter of style, a static. section that is used for configuration should print what it is doing, using --- as a print prefix.

  SHORT SYNTAX FOR SCOPING OBJECTS

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))

  MODULAR PROGRAMMING

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):

REFERENCES

  SEE ALSO

omake(1), omake-quickstart(1), omake-options(1), omake-root(1), omake-language(1), omake-shell(1), omake-rules(1), omake-base(1), omake-system(1), omake-pervasives(1), osh(1), make(1)

  VERSION

Version: 0.9.6.9 of April 11, 2006.

  LICENSE AND COPYRIGHT

(C)2003-2006, Mojave Group, Caltech

This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

  AUTHOR

Jason Hickey et. al..br Caltech 256-80
Pasadena, CA 91125, USA
Email: omake-devel@metaprl.org
WWW: http://www.cs.caltech.edu/~jyh