This file has been translated from LaTeX by HeVeA.

File: omake-doc, Node: Section 6-2,	Next: Section 6-3,	Prev: Section 6-1,	Up: Chapter 6
  

6.2   Functional evaluation
***************************

  
  This has two aspects: First of all, functions are values like other
values:
<<    p(f, x) =
          y = $(f $(x), 1)
          println($"The value is $(y)")
      p($(add), 5)       # prints 6
      p($(sub), 5)       # prints 4
>>
  
  The other aspect is that variables (and thus the whole environment)
can exist in several versions: The assignment to a variable creates
first a second version in the current block, and is not directly applied
to the orignal variable, unless it is finally "exported".
  (Note that in previous versions of the manual you could read here that
there "is no assignment operator". On the surface this is of course not
true, as we provide such an operator. This comment referred to the
implementation, which represents environments as functional maps from
names to values, and reduces assignment to a functional update of the
current environment, yielding to a new version.)

File: omake-doc, Node: Section 6-3,	Next: Section 6-4,	Prev: Section 6-2,	Up: Chapter 6
  

6.3   Exporting the environment
*******************************

    The export directive
can be used to propagate all or part of an inner scope back to its
parent. If used without arguments, the entire scope is propagated back
to the parent; otherwise the arguments specify which part of the
environment to propagate. The most common usage is to export some or all
of the definitions in a conditional block. In the following example, the
variable B is bound to 2 after the conditional. The A variable is not
redefined.
<<    if $(test)
         A = 1
         B = $(add $(A), 1)
         export B
      else
         B = 2
         export
>>
  
  If the export directive is used without an argument, all of the
following is exported: 
  
   - The values of all the dynamically scoped variables (as described in
   Section 5.5*Note Section 5-5::). 
   - The current working directory. 
   - The current Unix environment. 
   - The current implicit rules and implicit dependencies (see also
   Section 8.11.1*Note Subsection 8-11-1::). 
   - The current set of "phony" target declarations (see
   Sections 8.10*Note Section 8-10::
   and 8.11.3*Note Subsection 8-11-3::). 
  
  If the export directive is used with an argument, the argument
expression is evaluated and the resulting value is interpreted as
follows: 
  
   - If the value is empty, everything is exported, as described above. 
   - If the value represents a environment (or a partial environment)
   captured using the 'export' function, then the corresponding
   environment or partial environment is exported. 
   - Otherwise, the value must be a sequence of strings specifying which
   items are to be propagated back. The following strings have special
   meaning: 
     
      - .RULE --- implicit rules and implicit
      dependencies. 
      - .PHONY --- the set of "phony" target
      declarations. 
  All other strings are interpreted as names of the variables that need
   to be propagated back. 
  
  For example, in the following (somewhat artificial) example, the
variables A and B will be exported, and the implicit rule will remain in
the environment after the section ends, but the variable TMP and the
target tmp_phony will remain unchanged.
<<section
     A = 1
     B = 2
     TMP = $(add $(A), $(B))
  
     .PHONY: tmp_phony
  
     tmp_phony:
        prepare_foo
  
     %.foo: %.bar tmp_phony
        compute_foo $(TMP) $< $@
     export A B .RULE
>>
  
* Menu:

* Subsection 6-3-1::	Export regions
* Subsection 6-3-2::	Returning values from exported regions


File: omake-doc, Node: Subsection 6-3-1,	Next: Subsection 6-3-2,	Up: Section 6-3
  

6.3.1   Export regions
======================
  
  This feature was introduced in version 0.9.8.5.
  The export directive does not need to occur at the end of a block. An
export is valid from the point where it is specified to the end of the
block in which it is contained. In other words, the export is used in
the program that follows it. This can be especially useful for reducing
the amount of code you have to write. In the following example, the
variable CFLAGS is exported from the both branches of the conditional.
<<    export CFLAGS
      if $(equal $(OSTYPE), Win32)
          CFLAGS += /DWIN32
      else
          CFLAGS += -UWIN32
>>
  

File: omake-doc, Node: Subsection 6-3-2,	Prev: Subsection 6-3-1,	Up: Section 6-3
  

6.3.2   Returning values from exported regions
==============================================
  
  This feature was introduced in version 0.9.8.5.
  The use of export does not affect the value returned by a block. The
value is computed as usual, as the value of the last statement in the
block, ignoring the export. For example, suppose we wish to implement a
table that maps strings to unique integers. Consider the following
program.
<<    # Empty map
      table = $(Map)
  
      # Add an entry to the table
      intern(s) =
          export
          if $(table.mem $s)
              table.find($s)
          else
              private.i = $(table.length)
              table = $(table.add $s, $i)
              value $i
  
      intern(foo)
      intern(boo)
      intern(moo)
      # Prints "boo = 1"
      println($"boo = $(intern boo)")
>>
  Given a string s, the function intern returns either the value already
associated with s, or assigns a new value. In the latter case, the table
is updated with the new value. The export at the beginning of the
function means that the variable table is to be exported. The bindings
for s and i are not exported, because they are private.

  Evaluation in omake is eager. That is, expressions are evaluated as
soon as they are encountered by the evaluator. One effect of this is
that the right-hand-side of a variable definition is expanded when the
variable is defined.
<<    osh> A = 1
      - : "1"
      osh> A = $(A)$(A)
      - : "11"
>>
  
  In the second definition, A = $(A)$(A), the right-hand-side is
evaluated first, producing the sequence 11. Then the variable A is
redefined as the new value. When combined with dynamic scoping, this has
many of the same properties as conventional imperative programming.
<<    osh> A = 1
      - : "1"
      osh> printA() =
          println($"A = $A")
      osh> A = $(A)$(A)
      - : "11"
      osh> printA()
      11
>>
  
  In this example, the print function is defined in the scope of A. When
it is called on the last line, the dynamic value of A is 11, which is
what is printed.
  However, dynamic scoping and imperative programming should not be
confused. The following example illustrates a difference. The second
printA is not in the scope of the definition A = x$(A)$(A)x, so it
prints the original value, 1.
<<    osh> A = 1
      - : "1"
      osh> printA() =
          println($"A = $A")
      osh> section
               A = x$(A)$(A)x
               printA()
      x11x
      osh> printA()
      1
>>
  
  See also Section 7.7*Note Section 7-7:: for further ways to
control the evaluation order through the use of "lazy" expressions.

File: omake-doc, Node: Section 6-4,	Next: Section 6-5,	Prev: Section 6-3,	Up: Chapter 6
  

6.4   Objects
*************

  
  omake is an object-oriented language. Everything is an object,
including base values like numbers and strings. In many projects, this
may not be so apparent because most evaluation occurs in the default
toplevel object, the Pervasives object, and few other objects are ever
defined.
  However, objects provide additional means for data structuring, and in
some cases judicious use of objects may simplify your project.
  Objects are defined with the following syntax. This defines name to be
an object with several methods an values.
<<    name. =                     # += may be used as well
         extends parent-object    # optional
         class class-name         # optional
  
         # Fields
         X = value
         Y = value
  
         # Methods
         f(args) =
            body
         g(arg) =
            body
>>
  
  An extends directive specifies that this object inherits from the
specified parent-object. The object may have any number of extends
directives. If there is more than on extends directive, then fields and
methods are inherited from all parent objects. If there are name
conflicts, the later definitions override the earlier definitions.
  The class directive is optional. If specified, it defines a name for
the object that can be used in instanceof operations, as well as ::
scoping directives discussed below.
  The body of the object is actually an arbitrary program. The variables
defined in the body of the object become its fields, and the functions
defined in the body become its methods.

File: omake-doc, Node: Section 6-5,	Next: Section 6-6,	Prev: Section 6-4,	Up: Chapter 6
  

6.5   Field and method calls
****************************

  
  The fields and methods of an object are named using object.name
notation. For example, let's define a one-dimensional point value.
<<   Point. =
        class Point
  
        # Default value
        x = $(int 0)
  
        # Create a new point
        new(x) =
           x = $(int $(x))
           return $(this)
  
        # Move by one
        move() =
           x = $(add $(x), 1)
           return $(this)
  
     osh> p1 = $(Point.new 15)
     osh> value $(p1.x)
     - : 15 : Int
  
     osh> p2 = $(p1.move)
     osh> value $(p2.x)
     - : 16 : Int
>>
  
  The $(this) variable always represents the current object. The
expression $(p1.x) fetches the value of the x field in the p1 object.
The expression $(Point.new 15) represents a method call to the new
method of the Point object, which returns a new object with 15 as its
initial value. The expression $(p1.move) is also a method call, which
returns a new object at position 16.
  Note that objects are functional --- it is not possible to modify the
fields or methods of an existing object in place. Thus, the new and move
methods return new objects.

File: omake-doc, Node: Section 6-6,	Next: Section 6-7,	Prev: Section 6-5,	Up: Chapter 6
  

6.6   Method override
*********************

  
  Suppose we wish to create a new object that moves by 2 units, instead
of just 1. We can do it by overriding the move method.
<<   Point2. =
        extends $(Point)
  
        # Override the move method
        move() =
           x = $(add $(x), 2)
           return $(this)
  
     osh> p2 = $(Point2.new 15)
     osh> p3 = $(p2.move)
     osh> value $(p3.x)
     - : 17 : Int
>>
  
  However, by doing this, we have completely replaced the old move
method.

File: omake-doc, Node: Section 6-7,	Prev: Section 6-6,	Up: Chapter 6
  

6.7   Super calls
*****************

  
  Suppose we wish to define a new move method that just calls the old
one twice. We can refer to the old definition of move using a super
call, which uses the notation $(classname::name <args>). The classname
should be the name of the superclass, and name the field or method to be
referenced. An alternative way of defining the Point2 object is then as
follows.
<<   Point2. =
        extends $(Point)
  
        # Call the old method twice
        move() =
           this = $(Point::move)
           return $(Point::move)
>>
  
  Note that the first call to $(Point::move) redefines the current
object (the this variable). This is because the method returns a new
object, which is re-used for the second call.
   

File: omake-doc, Node: Chapter 7,	Next: Chapter 8,	Prev: Chapter 6,	Up: Top
  

Chapter 7     Additional language examples
******************************************
    
  In this section, we'll explore the core language through a series of
examples (examples of the build system are the topic of the
Chapter 3*Note Chapter 3::).
  For most of these examples, we'll use the osh command interpreter. For
simplicity, the values printed by osh have been abbreviated.
* Menu:

* Section 7-1::	Strings, arrays, and sequences
* Section 7-2::	Quoted strings
* Section 7-3::	Merging
* Section 7-4::	Arrays
* Section 7-5::	Files and directories
* Section 7-6::	Iteration, mapping, and foreach
* Section 7-7::	Lazy expressions
* Section 7-8::	Scoping and exports
* Section 7-9::	Shell aliases
* Section 7-10::	Input/output redirection on the cheap


File: omake-doc, Node: Section 7-1,	Next: Section 7-2,	Up: Chapter 7
  

7.1   Strings, arrays, and sequences
************************************

  
  The basic OMake values are strings, sequences, and arrays of values:
  
  
   - A string is immutable, and consists of bytes. 
   - An array is an immutable list of values that is automatically
   flattened, i.e. there is no distinction between an array of arrays
   and a simple array. 
   - A sequence can either behave as a string, and the member values are
   concatenated to a single string. Or, if the function expects an
   array, the sequence is considered as an array, and if needed, even
   split into elements. 
  
  How to define a string:
<<   osh> X = $"1 2"
     - : <data "1 2"> : String
>>
  
  Note that special characters trigger some pre-parsing, as in:
<<   osh> X = "1 2"
     - : <string "
            <data "1 2"> : String">
            : String
>>
  
  Despite the complex printing, the value of X is still "1 2" (including
double quotes). The double quotes as such do not have a meaning, but
they still cause that the space character is not considered as a
separator for the elements of a sequence, as in:
<<   osh> X = 1 2
     - : "1 2" : Sequence
     osh> addsuffix(.c, $X)
     - : <array 1.c 2.c> : Array
>>
  
  As addsuffix operates on arrays, the sequence is split into elements
before the suffices are added. The return value is an array.
  Sometimes you want to define an array explicitly. For this, use the []
brackets after the variable name, and list each array entry on a single
indented line.
<<   osh> A[] =
             Hello world
             $(getenv HOME)
     - : <array "Hello world" "/home/jyh"> : Array
>>
  
  One central property of arrays is that whitespace in the elements is
taken literally. This can be useful, especially for filenames that
contain whitespace. 
<<   # List the current files in the directory
      osh> ls -Q
      "fee"  "fi"  "foo"  "fum"
      osh> NAME[] = 
              Hello world
      - : <array "Hello world"> : Array
      osh> touch $(NAME)
      osh> ls -Q
      "fee"  "fi"  "foo"  "fum"  "Hello world"
>>
  
  As mentioned, nested arrays are automatically flattened:
<<    osh> a[] =
             1
             2
      osh> b[] =
             $(a)
             3
             $(a)
      - : <array
            <array "1" : Sequence "2" : Sequence> 
            "3" : Sequence
            <array "1" : Sequence "2" : Sequence> >
      osh> println($(length $(b)))
      5
>>
  
  The same holds for sequences when they are accessed as arrays.

File: omake-doc, Node: Section 7-2,	Next: Section 7-3,	Prev: Section 7-1,	Up: Chapter 7
  

7.2   Quoted strings
********************

    
  A String is a single value; whitespace is taken literally in a string.
Strings are introduced with quotes. There are four kinds of quoted
elements; the kind is determined by the opening quote. The symbols '
(single-quote) and " (double-quote) introduce the normal shell-style
quoted elements. The quotation symbols are included in the result
string. Variables are always expanded within a quote of this kind. Note
that the osh(1) (Chapter 15*Note Chapter 15::) printer escapes
double-quotes within the string; these are only for printing, they are
not part of the string itself.
<<    osh> A = 'Hello "world"'
      - : "'Hello \"world\"'" : String
      osh> B = "$(A)"
      - : "\"'Hello \"world\"'\"" : String
      osh> C = 'Hello \'world\''
      - : "'Hello 'world''" : String
>>
  
  The rationale for keeping the quotes as part of the string is that
this makes it very convenient to construct commands that are executed by
the Unix shell:
<<    osh> F = my thesis.pdf
      osh> G = picture of me.png
      osh> H = "$(F)" "$(G)"
      osh> ls $(H)
>>
  
  This constructs the command
<<ls "my thesis.pdf" "picture of me.png"
>>
  
  which is then executed by the shell. The quoting remains under the
control of the programmer (i.e. whether and how to quote).
  A second kind of quote is introduced with the $' and $" quotes. The
number of opening and closing quote symbols is arbitrary. These
quotations have several properties: 
  
   - The quote delimiters are not part of the string. 
   - Backslash \ symbols within the string are treated as normal
   characters. 
   - The strings may span several lines. 
   - Variables are expanded within $" sequences, but not within $'
   sequences. 
  
<<    osh> A = $'''Here $(IS) an '''' \(example\) string['''
      - : "Here $(IS) an '''' \\(example\\) string[" : String
      osh> B = $""""A is "$(A)" """"
      - : "A is \"Here $(IS) an '''' \\(example\\) string[\" " : String
      osh> value $(A.length)
      - : 38 : Int
      osh> value $(A.nth 5)
      - : "$" : String
      osh> value $(A.rev)
      - : "[gnirts )\\elpmaxe(\\ '''' na )SI($ ereH" : String
>>
  
  You can define an empty string as
<<    X =
>>
  
  but in expression context it is often more convenient to get the empty
string via the function call $(string).

File: omake-doc, Node: Section 7-3,	Next: Section 7-4,	Prev: Section 7-2,	Up: Chapter 7
  

7.3   Merging
*************

   
  Strings and sequences both have the property that they can be merged
with adjacent non-whitespace text.
<<    osh> A = a b c
      - : "a b c" : Sequence
      osh> B = $(A).c
      - : <sequence "a b c" : Sequence ".c" : Sequence> : Sequence
      osh> value $(nth 2, $(B))
      - : "c.c" : String
      osh> value $(length $(B))
      - : 3 : Int
>>
  
  Arrays are different. The elements of an array are never merged with
adjacent text of any kind (but are flattened into the enclosing array,
if any).

File: omake-doc, Node: Section 7-4,	Next: Section 7-5,	Prev: Section 7-3,	Up: Chapter 7
  

7.4   Arrays
************

   
  Arrays are defined by adding square brackets [] after a variable name
and defining the elements with an indented body. The elements may
include whitespace.
<<    osh> A[] =
              a b
              foo bar
      - : <array
             "a b" : Sequence
             "foo bar" : Sequence>
             : Array
      osh> echo $(A).c
      a b foo bar .c
      osh> value $(A.length)
      - : 2 : Int
      osh> value $(A.nth 1)
      - : "foo bar" : Sequence
>>
  
  Arrays are quite helpful on systems where filenames often contain
whitespace.
<<    osh> FILES[] =
               c:\Documents and Settings\jyh\one file
               c:\Program Files\omake\second file
  
      osh> CFILES = $(addsuffix .c, $(FILES))
      osh> echo $(CFILES)
      c:\Documents and Settings\jyh\one file.c c:\Program
Files\omake\second file.c
>>
  

File: omake-doc, Node: Section 7-5,	Next: Section 7-6,	Prev: Section 7-4,	Up: Chapter 7
  

7.5   Files and directories
***************************

  
  OMake projects usually span multiple directories, and different parts
of the project execute commands in different directories. There is a
need to define a location-independent name for a file or directory.
  This is done with the $(file <names>) and $(dir <names>) functions.
<<   osh> mkdir tmp
     osh> F = $(file fee)
     osh> section:
              cd tmp
              echo $F
     ../fee
     osh> echo $F
     fee
>>
  
  Note the use of a section: to limit the scope of the cd command. The
section temporarily changes to the tmp directory where the name of the
file is ../fee. Once the section completes, we are still in the current
directory, where the name of the file is fee.
  One common way to use the file functions is to define proper file
names in your project OMakefile, so that references within the various
parts of the project will refer to the same file.
<<    osh> cat OMakefile
      ROOT = $(dir .)
      TMP  = $(dir tmp)
      BIN  = $(dir bin)
      ...
>>
  

File: omake-doc, Node: Section 7-6,	Next: Section 7-7,	Prev: Section 7-5,	Up: Chapter 7
  

7.6   Iteration, mapping, and foreach
*************************************

  
  Most builtin functions operate transparently on arrays.
<<    osh> addprefix(-D, DEBUG WIN32)
      - : -DDEBUG -DWIN32 : Array
      osh> mapprefix(-I, /etc /tmp)
      - : -I /etc -I /tmp : Array
      osh> uppercase(fee fi foo fum)
      - : FEE FI FOO FUM : Array
>>
  
  The mapprefix and addprefix functions are slightly different (the
addsuffix and mapsuffix functions are similar). The addprefix adds the
prefex to each array element. The mapprefix doubles the length of the
array, adding the prefix as a new array element before each of the
original elements.
  Even though most functions work on arrays, there are times when you
will want to do it yourself. The foreach function is the way to go. The
foreach function has two forms, but the form with a body is most useful.
In this form, the function takes two arguments and a body. The second
argument is an array, and the first is a variable. The body is evaluated
once for each element of the array, where the variable is bound to the
element. Let's define a function to add 1 to each element of an array of
numbers.
<<   osh> add1(l) =
              foreach(i => $l):
                  add($i, 1)
     osh> add1(7 21 75)
     - : 8 22 76 : Array
>>
  
  Sometimes you have an array of filenames, and you want to define a
rule for each of them. Rules are not special, you can define them
anywhere a statement is expected. Say we want to write a function that
describes how to process each file, placing the result in the tmp/
directory.
<<   TMP = $(dir tmp)
  
     my-special-rule(files) =
        foreach(name => $(files))
           $(TMP)/$(name): $(name)
              process $< > $@
>>
  
  Later, in some other part of the project, we may decide that we want
to use this function to process some files.
<<   # These are the files to process in src/lib
     MY_SPECIAL_FILES[] =
         fee.src
         fi.src
         file with spaces in its name.src
     my-special-rule($(MY_SPECIAL_FILES))
>>
  
  The result of calling my-special-rule is exactly the same as if we had
written the following three rules explicitly.
<<    $(TMP)/fee.src: fee.src
          process fee > $@
      $(TMP)/fi.src: fi.src
          process fi.src > $@
      $(TMP)/$"file with spaces in its name.src": $"file with spaces in
its name.src"
          process $< > $@
>>
  
  Of course, writing these rules is not nearly as pleasant as calling
the function. The usual properties of function abstraction give us the
usual benefits. The code is less redundant, and there is a single
location (the my-special-rule function) that defines the build rule.
Later, if we want to modify/update the rule, we need do so in only one
location.

File: omake-doc, Node: Section 7-7,	Next: Section 7-8,	Prev: Section 7-6,	Up: Chapter 7
  

7.7   Lazy expressions
**********************

   
  Evaluation in omake is normally eager. That is, expressions are
evaluated as soon as they are encountered by the evaluator. One effect
of this is that the right-hand-side of a variable definition is expanded
when the variable is defined.
  There are two ways to control this behavior. The $`(v) form introduces
lazy behavior, and the $,(v) form restores eager behavior. Consider the
following sequence.
<<    osh> A = 1
      - : "1" : Sequence
      osh> B = 2
      - : "2" : Sequence
      osh> C = $`(add $(A), $,(B))
      - : $(apply add $(apply A) "2" : Sequence)
      osh> println(C = $(C))
      C = 3
      osh> A = 5
      - : "5" : Sequence
      osh> B = 6
      - : "6" : Sequence
      osh> println(C = $(C))
      C = 7
>>
  
  The definition C = $`(add $(A), $,(B)) defines a lazy application. The
add function is not applied in this case until its value is needed.
Within this expression, the value $,(B) specifies that B is to be
evaluated immediately, even though it is defined in a lazy expression.
  The first time that we print the value of C, it evaluates to 3 since A
is 1 and B is 2. The second time we evaluate C, it evaluates to 7
because A has been redefined to 5. The second definition of B has no
effect, since it was evaluated at definition time.
* Menu:

* Subsection 7-7-1::	A larger example of lazy expressions


File: omake-doc, Node: Subsection 7-7-1,	Up: Section 7-7
  

7.7.1   A larger example of lazy expressions
============================================
  
  Lazy expressions are not evaluated until their result is needed. Some
people, including this author, frown on overuse of lazy expressions,
mainly because it is difficult to know when evaluation actually happens.
However, there are cases where they pay off.
  One example comes from option processing. Consider the specification
of "include" directories on the command line for a C compiler. If we
want to include files from /home/jyh/include and ../foo, we specify it
on the command line with the options -I/home/jyh/include -I../foo.
  Suppose we want to define a generic rule for building C files. We
could define a INCLUDES array to specify the directories to be included,
and then define a generic implicit rule in our root OMakefile.
<<    # Generic way to compile C files.
      CFLAGS = -g
      INCLUDES[] =
      %.o: %.c
         $(CC) $(CFLAGS) $(INCLUDES) -c $<
  
      # The src directory builds my_widget+ from 4 source files.
      # It reads include files from the include directory.
      .SUBDIRS: src
          FILES = fee fi foo fum
          OFILES = $(addsuffix .o, $(FILES))
          INCLUDES[] += -I../include
          my_widget: $(OFILES)
             $(CC) $(CFLAGS) -o $@ $(OFILES)
>>
  
  But this is not quite right. The problem is that INCLUDES is an array
of options, not directories. If we later wanted to recover the
directories, we would have to strip the leading -I prefix, which is a
hassle. Furthermore, we aren't using proper names for the directories.
The solution here is to use a lazy expression. We'll define INCLUDES as
a directory array, and a new variable PREFIXED_INCLUDES that adds the -I
prefix. The PREFIXED_INCLUDES is computed lazily, ensuring that the
value uses the most recent value of the INCLUDES variable.
<<    # Generic way to compile C files.
      CFLAGS = -g
      INCLUDES[] =
      PREFIXED_INCLUDES[] = $`(addprefix -I, $(INCLUDES))
      %.o: %.c
         $(CC) $(CFLAGS) $(PREFIXED_INCLUDES) -c $<
  
      # For this example, we define a proper name for the include
directory
      STDINCLUDE = $(dir include)
  
      # The src directory builds my_widget+ from 4 source files.
      # It reads include files from the include directory.
      .SUBDIRS: src
          FILES = fee fi foo fum
          OFILES = $(addsuffix .o, $(FILES))
          INCLUDES[] += $(STDINCLUDE)
          my_widget: $(OFILES)
             $(CC) $(CFLAGS) -o $@ $(OFILES)
>>
  
  Note that there is a close connection between lazy values and
functions. In the example above, we could equivalently define
PREFIXED_INCLUDES as a function with zero arguments.
<<    PREFIXED_INCLUDES() =
          addprefix(-I, $(INCLUDES))
>>
  

File: omake-doc, Node: Section 7-8,	Next: Section 7-9,	Prev: Section 7-7,	Up: Chapter 7
  

7.8   Scoping and exports
*************************

  
  The OMake language is functional (apart from IO and shell commands).
This comes in two parts: functions are first-class, and variables are
immutable (there is no assignment operator). The latter property may
seem strange to users used to GNU make, but it is actually a central
point of OMake. Since variables can't be modified, it is impossible (or
at least hard) for one part of the project to interfere with another.
  To be sure, pure functional programming can be awkward. In OMake, each
new indentation level introduces a new scope, and new definitions in
that scope are lost when the scope ends. If OMake were overly strict
about scoping, we would wind up with a lot of convoluted code.
<<   osh> X = 1
     osh> setenv(BOO, 12)
     osh> if $(equal $(OSTYPE), Win32)
              setenv(BOO, 17)
              X = 2
     osh> println($X $(getenv BOO))
     1 12
>>
  
  The export command presents a way out. It takes care of "exporting" a
value (or the entire variable environment) from an inner scope to an
outer one.
<<   osh> X = 1
     osh> setenv(BOO, 12)
     osh> if $(equal $(OSTYPE), Win32)
              setenv(BOO, 17)
              X = 2
              export
     osh> println($X $(getenv BOO))
     2 17
>>
  
  Exports are especially useful in loop to export values from one
iteration of a loop to the next.
<<   # Ok, let's try to add up the elements of the array
     osh>sum(l) =
             total = 0
             foreach(i => $l)
                 total = $(add $(total), $i)
             value $(total)
     osh>sum(1 2 3)
     - : 0 : Int
  
     # Oops, that didn't work!
     osh>sum(l) =
             total = 0
             foreach(i => $l)
                 total = $(add $(total), $i)
                 export
             value $(total)
     osh>sum(1 2 3)
     - : 6 : Int
>>
  
  A while loop is another form of loop, with an auto-export.
<<    osh>i = 0
      osh>total = 0
      osh>while $(lt $i, 10)
              total = $(add $(total), $i)
              i = $(add $i, 1)
      osh>println($(total))
      45
>>
  

File: omake-doc, Node: Section 7-9,	Next: Section 7-10,	Prev: Section 7-8,	Up: Chapter 7
  

7.9   Shell aliases
*******************

  
  Sometimes you may want to define an alias, an OMake command that
masquerades as a real shell command. You can do this by adding your
function as a method to the Shell object.
  For an example, suppose we use the awk function to print out all the
comments in a file.
<<    osh>cat comment.om
      # Comment function
      comments(filename) =
          awk($(filename))
          case $'^#'
              println($0)
      # File finished
      osh>include comment
      osh>comments(comment.om)
      # Comment function
      # File finished
>>
  
  To add it as an alias, add the method (using += to preserve the
existing entries in the Shell).
<<   osh>Shell. +=
             printcom(argv) =
                 comments($(nth 0, $(argv)))
     osh>printcom comment.om > output.txt
     osh>cat output.txt
     # Comment function
     # File finished
>>
  
  A shell command is passed an array of arguments argv. This does not
include the name of the alias.

File: omake-doc, Node: Section 7-10,	Prev: Section 7-9,	Up: Chapter 7
  

7.10   Input/output redirection on the cheap
********************************************

  
  As it turns out, scoping also provides a nice alternate way to perform
redirection. Suppose you have already written a lot of code that prints
to the standard output channel, but now you decide you want to redirect
it. One way to do it is using the technique in the previous example:
define your function as an alias, and then use shell redirection to
place the output where you want.
  There is an alternate method that is easier in some cases. The
variables stdin, stdout, and stderr define the standard I/O channels. To
redirect output, redefine these variables as you see fit. Of course, you
would normally do this in a nested scope, so that the outer channels are
not affected.
<<    osh>f() =
              println(Hello world)
      osh>f()
      Hello world
      osh>section:
              stdout = $(fopen output.txt, w)
              f()
              close($(stdout))
      osh>cat output.txt
      Hello world
>>
  
  This also works for shell commands. If you like to gamble, you can try
the following example.
<<    osh>f() =
              println(Hello world)
      osh>f()
      Hello world
      osh>section:
              stdout = $(fopen output.txt, w)
              f()
              cat output.txt
              close($(stdout))
      osh>cat output.txt
      Hello world
      Hello world
>>
  
   

File: omake-doc, Node: Chapter 8,	Next: Chapter 9,	Prev: Chapter 7,	Up: Top
  

Chapter 8     Rules
*******************
    
  Rules are used by OMake to specify how to build files. At its
simplest, a rule has the following form.
<<    <target>: <dependencies>
          <commands>
>>
  
  The <target> is the name of a file to be built. The <dependencies> are
a list of files that are needed before the <target> can be built. The
<commands> are a list of indented lines specifying commands to build the
target. For example, the following rule specifies how to compile a file
hello.c.
<<    hello.o: hello.c
          $(CC) $(CFLAGS) -c -o hello.o hello.c
>>
  
  This rule states that the hello.o file depends on the hello.c file. If
the hello.c file has changed, the command $(CC) $(CFLAGS) -c -o hello.o
hello.c is to be executed to update the target file hello.o.
  A rule can have an arbitrary number of commands. The individual
command lines are executed independently by the command shell. The
commands do not have to begin with a tab, but they must be indented from
the dependency line.
  In addition to normal variables, the following special variables may
be used in the body of a rule.
  
  
   - $*: the target name,
   without a suffix. 
   - $@: the target name. 
   - $^: a list of the sources,
   in alphabetical order, with duplicates removed. 
   - $+: all the sources, in
   the original order. 
   - $<: the first source. 
  
  For example, the above hello.c rule may be simplified as follows.
<<    hello.o: hello.c
          $(CC) $(CFLAGS) -c -o $@ $<
>>
  
  Unlike normal values, the variables in a rule body are expanded
lazily, and binding is dynamic. The following function definition
illustrates some of the issues.
<<    CLibrary(name, files) =
          OFILES = $(addsuffix .o, $(files))
  
          $(name).a: $(OFILES)
              $(AR) cq $@ $(OFILES)
>>
  
  This function defines a rule to build a program called $(name) from a
list of .o files. The files in the argument are specified without a
suffix, so the first line of the function definition defines a variable
OFILES that adds the .o suffix to each of the file names. The next step
defines a rule to build a target library $(name).a from the $(OFILES)
files. The expression $(AR) is evaluated when the function is called,
and the value of the variable AR is taken from the caller's scope (see
also the section on Scoping).
* Menu:

* Section 8-1::	Implicit rules
* Section 8-2::	Bounded implicit rules
* Section 8-3::	section
* Section 8-4::	section rule
* Section 8-5::	Special dependencies
* Section 8-6::	'.SCANNER' rules
* Section 8-7::	.DEFAULT
* Section 8-8::	.SUBDIRS
* Section 8-9::	.INCLUDE
* Section 8-10::	.PHONY
* Section 8-11::	Rule scoping
* Section 8-12::	Running OMake from a subdirectory
* Section 8-13::	Pathnames in rules


File: omake-doc, Node: Section 8-1,	Next: Section 8-2,	Up: Chapter 8
  

8.1   Implicit rules
********************

   
  Rules may also be implicit. That is, the files may be specified by
wildcard patterns. The wildcard character is %. For example, the
following rule specifies a default rule for building .o files.
<<    %.o: %.c
          $(CC) $(CFLAGS) -c -o $@ $*.c
>>
  
  This rule is a template for building an arbitrary .o file from a .c
file.
  By default, implicit rules are only used for the targets in the
current directory. However subdirectories included via the .SUBDIRS
rules inherit all the implicit rules that are in scope (see also the
section on Scoping).

File: omake-doc, Node: Section 8-2,	Next: Section 8-3,	Prev: Section 8-1,	Up: Chapter 8
  

8.2   Bounded implicit rules
****************************

   
  Implicit rules may specify the set of files they apply to. The
following syntax is used.
<<    <targets>: <pattern>: <dependencies>
          <commands>
>>
  
  For example, the following rule applies only to the files a.o and b.o.
<<   a.o b.o: %.o: %.c
          $(CC) $(CFLAGS) -DSPECIAL -c $*.c
>>
  

File: omake-doc, Node: Section 8-3,	Next: Section 8-4,	Prev: Section 8-2,	Up: Chapter 8
  

8.3   section
*************

   
  Frequently, the commands in a rule body are expressions to be
evaluated by the shell. omake also allows expressions to be evaluated by
omake itself.
  The syntax of these "computed rules" uses the section expression. The
following rule uses the omake IO functions to produce the target
hello.c.
<<    hello.c:
          section
              FP = fopen(hello.c, w)
              fprintln($(FP), $""#include <stdio.h> int main() {
printf("Hello world\n"); }"")
              close($(FP))
>>
  
  This example uses the quotation $""..."" (see also
Section B.1.6*Note Subsection B-1-6::) to quote the text being
printed. These quotes are not included in the output file. The fopen,
fprintln, and close functions perform file IO as discussed in the IO
section.
  In addition, commands that are function calls, or special expressions,
are interpreted correctly. Since the fprintln function can take a file
directly, the above rule can be abbreviated as follows.
<<    hello.c:
         fprintln($@, $""#include <stdio.h> int main() { printf("Hello
world\n"); }"")
>>
  

File: omake-doc, Node: Section 8-4,	Next: Section 8-5,	Prev: Section 8-3,	Up: Chapter 8
  

8.4   section rule
******************

   
  Rules can also be computed using the section rule form, where a rule
body is expected instead of an expression. In the following rule, the
file a.c is copied onto the hello.c file if it exists, otherwise hello.c
is created from the file default.c.
<<    hello.c:
          section rule
             if $(target-exists a.c)
                hello.c: a.c
                   cat a.c > hello.c
             else
                hello.c: default.c
                   cp default.c hello.c
>>
  

File: omake-doc, Node: Section 8-5,	Next: Section 8-6,	Prev: Section 8-4,	Up: Chapter 8
  

8.5   Special dependencies
**************************

   
* Menu:

* Subsection 8-5-1::	:exists:
* Subsection 8-5-2::	:effects:
* Subsection 8-5-3::	:value:


File: omake-doc, Node: Subsection 8-5-1,	Next: Subsection 8-5-2,	Up: Section 8-5
  

8.5.1   :exists:
================
   
  In some cases, the contents of a dependency do not matter, only
whether the file exists or not. In this case, the :exists: qualifier can
be used for the dependency.
<<    foo.c: a.c :exists: .flag
         if $(test -e .flag)
             $(CP) a.c $@
>>
  

File: omake-doc, Node: Subsection 8-5-2,	Next: Subsection 8-5-3,	Prev: Subsection 8-5-1,	Up: Section 8-5
  

8.5.2   :effects:
=================
   
  Some commands produce files by side-effect. For example, the latex(1)
command produces a .aux file as a side-effect of producing a .dvi file.
In this case, the :effects: qualifier can be used to list the
side-effect explicitly. omake is careful to avoid simultaneously running
programs that have overlapping side-effects.
<<    paper.dvi: paper.tex :effects: paper.aux
          latex paper
>>
  

File: omake-doc, Node: Subsection 8-5-3,	Prev: Subsection 8-5-2,	Up: Section 8-5
  

8.5.3   :value:
===============
   
  The :value: dependency is used to specify that the rule execution
depends on the value of an expression. For example, the following rule
<<    a: b c :value: $(X)
          ...
>>
  
  specifies that "a" should be recompiled if the value of $(X) changes
(X does not have to be a filename). This is intended to allow greater
control over dependencies.
  In addition, it can be used instead of other kinds of dependencies.
For example, the following rule:
<<    a: b :exists: c
          commands
>>
  
  is the same as
<<    a: b :value: $(target-exists c)
          commands
>>
  
  Notes: 
  
   - The values are arbitrary (they are not limited to variables) 
   - The values are evaluated at rule expansion time, so expressions
   containing variables like $@, $^, etc are legal. 
  

File: omake-doc, Node: Section 8-6,	Next: Section 8-7,	Prev: Section 8-5,	Up: Chapter 8
  

8.6   '.SCANNER' rules
**********************

   
  Scanner rules define a way to specify automatic dependency scanning. A
.SCANNER rule has the following form.
<<    .SCANNER: target: dependencies
          commands
>>
  
  The rule is used to compute additional dependencies that might be
defined in the source files for the specified target. The result of
executing the scanner commands must be a sequence of dependencies in
OMake format, printed to the standard output. For example, on GNU
systems the gcc -MM foo.c produces dependencies for the file foo.c
(based on #include information).
  We can use this to specify a scanner for C files that adds the scanned
dependencies for the .o file. The following scanner specifies that
dependencies for a file, say foo.o can be computed by running gcc -MM
foo.c. Furthermore, foo.c is a dependency, so the scanner should be
recomputed whenever the foo.c file changes.
<<    .SCANNER: %.o: %.c
          gcc -MM $<
>>
  
  Let's suppose that the command gcc -MM foo.c prints the following
line.
<<    foo.o: foo.h /usr/include/stdio.h
>>
  
  The result is that the files foo.h and /usr/include/stdio.h are
considered to be dependencies of foo.o---that is, foo.o should be
rebuilt if either of these files changes.
  This works, to an extent. One nice feature is that the scanner will be
re-run whenever the foo.c file changes. However, one problem is that
dependencies in C are recursive. That is, if the file foo.h is modified,
it might include other files, establishing further dependencies. What we
need is to re-run the scanner if foo.h changes too.
  We can do this with a value dependency. The variable $& is defined as
the dependency results from any previous scan. We can add these as
dependencies using the digest function, which computes an MD5 digest of
the files.
<<    .SCANNER: %.o: %.c :value: $(digest $&)
          gcc -MM $<
>>
  
  Now, when the file foo.h changes, its digest will also change, and the
scanner will be re-run because of the value dependency (since $& will
include foo.h).
  This still is not quite right. The problem is that the C compiler uses
a search-path for include files. There may be several versions of the
file foo.h, and the one that is chosen depends on the include path. What
we need is to base the dependencies on the search path.
  The $(digest-in-path-optional ...) function computes the digest based
on a search path, giving us a solution that works.
<<    .SCANNER: %.o: %.c :value: $(digest-in-path-optional $(INCLUDES),
$&)
         gcc -MM $(addprefix -I, $(INCLUDES)) $<
>>
  
  The standard output of the scanner rules will be captured by OMake and
is not allowed to contain any content that OMake will not be able to
parse as a dependency. The output is allowed to contain dependency
specifications for unrelated targets, however such dependencies will be
ignored. The scanner rules are allowed to produce arbitrary output on
the standard error channel --- such output will be handled in the same
way as the output of the ordinary rules (in other words, it will be
presented to the user, when dictated by the --output-... options
enabled).
  Additional examples of the .SCANNER rules can be found in
Section 3.4.3*Note Subsection 3-4-3::.
* Menu:

* Subsection 8-6-1::	Named scanners, and the ':scanner:' dependencies
* Subsection 8-6-2::	Notes


File: omake-doc, Node: Subsection 8-6-1,	Next: Subsection 8-6-2,	Up: Section 8-6
  

8.6.1   Named scanners, and the ':scanner:' dependencies
========================================================
   
  Sometimes it may be useful to specify explicitly which scanner should
be used in a rule. For example, we might compile .c files with different
options, or (heaven help us) we may be using both gcc and the Microsoft
Visual C++ compiler cl. In general, the target of a .SCANNER is not tied
to a particular target, and we may name it as we like.
<<    .SCANNER: scan-gcc-%.c: %.c :value: $(digest-in-path-optional
$(INCLUDES), $&)
          gcc -MM $(addprefix -I, $(INCLUDES)) $<
  
      .SCANNER: scan-cl-%.c: %.c :value: $(digest-in-path-optional
$(INCLUDES), $&)
          cl --scan-dependencies-or-something $(addprefix /I,
$(INCLUDES)) $<
>>
  
  The next step is to define explicit scanner dependencies. The
:scanner: dependency is used for this. In this case, the scanner
dependencies are specified explicitly.
<<    $(GCC_FILES): %.o: %.c :scanner: scan-gcc-%.c
          gcc ...
  
      $(CL_FILES): %.obj: %.c :scanner: scan-cl-%.c
          cl ...
>>
  
  Explicit :scanner: scanner specification may also be used to state
that a single .SCANNER rule should be used to generate dependencies for
more than one target. For example,
<<    .SCANNER: scan-all-c: $(GCC_FILES) :value:
$(digest-in-path-optional $(INCLUDES), $&)
          gcc -MM $(addprefix -I, $(INCLUDES)) $(GCC_FILES)
  
      $(GCC_FILES): %.o: %.c :scanner: scan-all-c
          ...
>>
  
  The above has the advantage of only running gcc once and a
disadvantage that when a single source file changes, all the files will
end up being re-scanned.

File: omake-doc, Node: Subsection 8-6-2,	Prev: Subsection 8-6-1,	Up: Section 8-6
  

8.6.2   Notes
=============
  
  In most cases, you won't need to define scanners of your own. The
standard installation includes default scanners (both explicitly and
implicitly named ones) for C, OCaml, and LaTeX files.
  The 'SCANNER_MODE' variable controls the usage of implicit scanner
dependencies.
  The explicit :scanner: dependencies reduce the chances of scanner
mis-specifications. In large complicated projects it might be a good
idea to set SCANNER_MODE to error and use only the named .SCANNER rules
and explicit :scanner: specifications.

File: omake-doc, Node: Section 8-7,	Next: Section 8-8,	Prev: Section 8-6,	Up: Chapter 8
  

8.7   .DEFAULT
**************

   
  The .DEFAULT target specifies a target to be built by default if omake
is run without explicit targets. The following rule instructs omake to
build the program hello by default
<<   .DEFAULT: hello
>>
  

File: omake-doc, Node: Section 8-8,	Next: Section 8-9,	Prev: Section 8-7,	Up: Chapter 8
  

8.8   .SUBDIRS
**************

   
  The .SUBDIRS target is used to specify a set of subdirectories that
are part of the project. Each subdirectory should have its own
OMakefile, which is evaluated in the context of the current environment.
<<   .SUBDIRS: src doc tests
>>
  
  This rule specifies that the OMakefiles in each of the src, doc, and
tests directories should be read.
  In some cases, especially when the OMakefiles are very similar in a
large number of subdirectories, it is inconvenient to have a separate
OMakefile for each directory. If the .SUBDIRS rule has a body, the body
is used instead of the OMakefile.
<<   .SUBDIRS: src1 src2 src3
        println(Subdirectory $(CWD))
        .DEFAULT: lib.a
>>
  
  In this case, the src1, src2, and src3 files do not need OMakefiles.
Furthermore, if one exists, it is ignored. The following includes the
file if it exists.
<<   .SUBDIRS: src1 src2 src3
         if $(file-exists OMakefile)
            include OMakefile
         .DEFAULT: lib.a
>>
  

File: omake-doc, Node: Section 8-9,	Next: Section 8-10,	Prev: Section 8-8,	Up: Chapter 8
  

8.9   .INCLUDE
**************

   
  The .INCLUDE target is like the include directive, but it specifies a
rule to build the file if it does not exist.
<<   .INCLUDE: config
         echo "CONFIG_READ = true" > config
  
      echo CONFIG_READ is $(CONFIG_READ)
>>
  
  You may also specify dependencies to an .INCLUDE rule.
<<   .INCLUDE: config: config.defaults
        cp config.defaults config
>>
  
  A word of caution is in order here. The usual policy is used for
determining when the rule is out-of-date. The rule is executed if any of
the following hold.
  
  
   - the target does not exist, 
   - the rule has never been executed before, 
   - any of the following have changed since the last time the rule was
   executed, 
     
      - the target, 
      - the dependencies, 
      - the commands-text. 
  
  
  In some of the cases, this will mean that the rule is executed even if
the target file already exists. If the target is a file that you expect
to edit by hand (and therefore you don't want to overwrite it), you
should make the rule evaluation conditional on whether the target
already exists.
<<   .INCLUDE: config: config.defaults
         # Don't overwrite my carefully hand-edited file
         if $(not $(file-exists config))
            cp config.defaults config
>>
  

File: omake-doc, Node: Section 8-10,	Next: Section 8-11,	Prev: Section 8-9,	Up: Chapter 8
  

8.10   .PHONY
*************

   
  A "phony" target is a target that is not a real file, but exists to
collect a set of dependencies. Phony targets are specified with the
.PHONY rule. In the following example, the install target does not
correspond to a file, but it corresponds to some commands that should be
run whenever the install target is built (for example, by running omake
install).
<<   .PHONY: install
  
     install: myprogram.exe
        cp myprogram.exe /usr/bin
>>
  

File: omake-doc, Node: Section 8-11,	Next: Section 8-12,	Prev: Section 8-10,	Up: Chapter 8
  

8.11   Rule scoping
*******************

   
  As we have mentioned before, omake is a scoped language. This provides
great flexibility---different parts of the project can define different
configurations without interfering with one another (for example, one
part of the project might be compiled with CFLAGS=-O3 and another with
CFLAGS=-g).
  But how is the scope for a target file selected? Suppose we are
building a file dir/foo.o. omake uses the following rules to determine
the scope.
  
  
   - First, if there is an explicit rule for building dir/foo.o (a rule
   with no wildcards), the context for that rule determines the scope
   for building the target. 
   - Otherwise, the directory dir/ must be part of the project. This
   normally means that a configuration file dir/OMakefile exists
   (although, see the .SUBDIRS section for another way to specify the
   OMakefile). In this case, the scope of the target is the scope at the
   end of the dir/OMakefile. 
  
  To illustrate rule scoping, let's go back to the example of a "Hello
world" program with two files. Here is an example OMakefile (the two
definitions of CFLAGS are for illustration).
<<    # The executable is compiled with debugging
      CFLAGS = -g
      hello: hello_code.o hello_lib.o
         $(CC) $(CFLAGS) -o $@ $+
  
      # Redefine CFLAGS
      CFLAGS += -O3
>>
  
  In this project, the target hello is explicit. The scope of the hello
target is the line beginning with hello:, where the value of CFLAGS is
-g. The other two targets, hello_code.o and hello_lib.o do not appear as
explicit targets, so their scope is at the end of the OMakefile, where
the CFLAGS variable is defined to be -g -O3. That is, hello will be
linked with CFLAGS=-g and the .o files will be compiled with CFLAGS=-g
-O3.
  We can change this behavior for any of the targets by specifying them
as explicit targets. For example, suppose we wish to compile hello_lib.o
with a preprocessor variable LIBRARY.
<<    # The executable is compiled with debugging
      CFLAGS = -g
      hello: hello_code.o hello_lib.o
         $(CC) $(CFLAGS) -o $@ $+
  
      # Compile hello_lib.o with CFLAGS = -g -DLIBRARY
      section
          CFLAGS += -DLIBRARY
          hello_lib.o:
  
      # Redefine CFLAGS
      CFLAGS += -O3
>>
  
  In this case, hello_lib.o is also mentioned as an explicit target, in
a scope where CFLAGS=-g -DLIBRARY. Since no rule body is specified, it
is compiled using the usual implicit rule for building .o files (in a
context where CFLAGS=-g -DLIBRARY).
* Menu:

* Subsection 8-11-1::	Scoping of implicit rules
* Subsection 8-11-2::	Scoping of '.SCANNER' rules
* Subsection 8-11-3::	Scoping for '.PHONY' targets

