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# Chapter 9 Base library

- Builtin variables
- Logic, Boolean functions, and control flow
- Arrays and sequences
- Arithmetic
- First-class functions
- Iteration and mapping
- Boolean tests

## 9.1 Builtin variables

##### OMAKE_VERSION

Version of OMake.

##### STDLIB

The directory where the OMake standard library files reside. At startup, the default value is determined as follows.

- The value of the `OMAKELIB` environment variable, if set (must contain an absolute path, if set), otherwise
- On Windows, the registry keys `HKEY_CURRENT_USER\SOFTWARE\MetaPRL\OMake\OMAKELIB` and `HKEY_LOCAL_MACHINE\SOFTWARE\MetaPRL\OMake\OMAKELIB` are looked up and the value is used, if exist.
- Otherwise a compile-time default it used.

The current default value may be accessed by running `omake --version`

##### OMAKEPATH

An array of directories specifying the lookup path for the `include` and `open` directives (see Section 4.7). The default value is an array of two elements — `.` and `$(STDLIB)`.

##### OSTYPE

Set to the machine architecture `omake` is running on. Possible values are `Unix` (for all Unix versions, including Linux and Mac OS X), `Win32` (for MS-Windows, OMake compiled with MSVC++ or Mingw), and `Cygwin` (for MS-Windows, OMake compiled with Cygwin).

##### SYSNAME

The name of the operating system for the current machine.

##### NODENAME

The hostname of the current machine.

##### OS_VERSION

The operating system release.

##### MACHINE

The machine architecture, e.g. `i386`, `sparc`, etc.

##### HOST

Same as `NODENAME`.

##### USER

The login name of the user executing the process.

##### HOME

The home directory of the user executing the process.

##### PID

The OMake process id.

##### TARGETS

The command-line target strings. For example, if OMake is invoked with the following command line,

          omake CFLAGS=1 foo bar.c

then `TARGETS` is defined as `foo bar.c`.

##### BUILD_SUMMARY

The `BUILD_SUMMARY` variable refers to the file that `omake` uses to summarize a build (the message that is printed at the very end of a build). The file is empty when the build starts. If you wish to add additional messages to the build summary, you can edit/modify this file during the build.

For example, if you want to point out that some action was taken, you can append a message to the build summary.

       foo: boo
           echo "The file foo was built" >> $(BUILD_SUMMARY)
           ...build foo...

##### VERBOSE

Whether certain commands should be verbose. A boolean flag that is `false` by default and is set to `true` when OMake is invoked with the `--verbose` option.

## 9.2 Logic, Boolean functions, and control flow

Boolean values in omake are represented by case-insensitive strings. The false value can be represented by the strings `false`, `no`, `nil`, `undefined` or `0`, and everything else is true.

### 9.2.1 not

       $(not e) : String
          e : String

The `not` function negates a Boolean value.

For example, `$(not false)` expands to the string `true`, and `$(not hello world)` expands to `false`.

### 9.2.2 equal

       $(equal e1, e2) : String
          e1 : String
          e2 : String

The `equal` function tests for equality of two values.

For example `$(equal a, b)` expands to `false`, and `$(equal hello world, hello world)` expands to `true`.

### 9.2.3 and

        $(and e1, ..., en) : String
           e1, ..., en: Sequence

The `and` function evaluates to the conjunction of its arguments.

For example, in the following code, `X` is true, and `Y` is false.

        A = a
        B = b
        X = $(and $(equal $(A), a) true $(equal $(B), b))
        Y = $(and $(equal $(A), a) true $(equal $(A), $(B)))

### 9.2.4 or

       $(or e1, ..., en) : String
          e1, ..., en: String Sequence

The `or` function evaluates to the disjunction of its arguments.

For example, in the following code, `X` is true, and `Y` is false.

        A = a
        B = b
        X = $(or $(equal $(A), a) false $(equal $(A), $(B)))
        Y = $(or $(equal $(A), $(B)) $(equal $(A), b))

### 9.2.5 if

        $(if e1, e2[, e3]) : value
           e1 : String
           e2, e3 : value

The `if` function represents a conditional based on a Boolean value. For example `$(if $(equal a, b), c, d)` evaluates to `d`.

Conditionals may also be declared with an alternate syntax.

       if e1
          body1
       elseif e2
          body2
       ...
       else
          bodyn

If the expression `e1` is not false, then the expressions in `body1` are evaluated and the result is returned as the value of the conditional. Otherwise, if `e1` evaluates to false, the evaluation continues with the `e2` expression. If none of the conditional expressions is true, then the expressions in `bodyn` are evaluated and the result is returned as the value of the conditional.

There can be any number of `elseif` clauses; the `else` clause is optional.

Note that each branch of the conditional defines its own scope, so variables defined in the branches are normally not visible outside the conditional. The `export` command may be used to export the variables defined in a scope. For example, the following expression represents a common idiom for defining the C compiler configuration.

       if $(equal $(OSTYPE), Win32)
          CC = cl
          CFLAGS += /DWIN32
          export
       else
          CC = gcc
          CFLAGS += -g -O2
          export

### 9.2.6 switch, match

The `switch` and `match` functions perform pattern matching.

`$(switch <arg>, <pattern_1>, <value_1>, ..., <pattern_n>, <value_n>)` `$(match <arg>, <pattern_1>, <value_1>, ..., <pattern_n>, <value_n>)`

The number of `<pattern>/<value>` pairs is arbitrary. They strictly alternate; the total number of arguments to `<match>` must be odd.

The `<arg>` is evaluated to a string, and compared with `<pattern_1>`. If it matches, the result of the expression is `<value_1>`. Otherwise evaluation continues with the remaining patterns until a match is found. If no pattern matches, the value is the empty string.

The `switch` function uses string comparison to compare the argument with the patterns. For example, the following expression defines the `FILE` variable to be either `foo`, `bar`, or the empty string, depending on the value of the `OSTYPE` variable.

        FILE = $(switch $(OSTYPE), Win32, foo, Unix, bar)

The `match` function uses regular expression patterns (see the `grep` function). If a match is found, the variables `$1, $2, ...` are bound to the substrings matched between `\(` and `\)` delimiters. The `$0` variable contains the entire match, and `$*` is an array of the matched substrings. to the matched substrings.

        FILE = $(match foo_xyz/bar.a, foo_\\\(.*\\\)/\\\(.*\\\)\.a, foo_$2/$1.o)

The `switch` and `match` functions also have an alternate (more usable) form.

       match e
       case pattern1
          body1
       case pattern2
          body2
       ...
       default
          bodyd

If the value of expression `e` matches `pattern_i` and no previous pattern, then `body_i` is evaluated and returned as the result of the `match`. The `switch` function uses string comparison; the `match` function uses regular expression matching.

       match $(FILE)
       case $".*\(\.[^\/.]*\)"
          println(The string $(FILE) has suffix $1)
       default
          println(The string $(FILE) has no suffix)

### 9.2.7 try

       try
          try-body
       catch class1(v1)
          catch-body
       when expr
          when-body
       ...
       finally
          finally-body

The `try` form is used for exception handling. First, the expressions in the `try-body` are evaluated.

If evaluation results in a value `v` without raising an exception, then the expressions in the `finally-body` are evaluated and the value `v` is returned as the result.

If evaluation of the `try-body` results in a exception object `obj`, the `catch` clauses are examined in order. When examining `catch` clause `catch class(v)`, if the exception object `obj` is an instance of the class name `class`, the variable `v` is bound to the exception object, and the expressions in the `catch-body` are evaluated.

If a `when` clause is encountered while a `catch` body is being evaluated, the predicate `expr` is evaluated. If the result is true, evaluation continues with the expressions in the `when-body`. Otherwise, the next `catch` clause is considered for evaluation.

If evaluation of a `catch-body` or `when-body` completes successfully, returning a value `v`, without encountering another `when` clause, then the expressions in the `finally-body` are evaluated and the value `v` is returned as the result.

There can be any number of `catch` clauses; the `finally` clause is optional.

### 9.2.8 raise

       raise exn
          exn : Exception

The `raise` function raises an exception. The `exn` object can be any object. However, the normal convention is to raise an `Exception` object.

If the exception is never caught, the whole object will be verbosely printed in the error message. However, if the object is an `Exception` one and contains a `message` field, only that field will be included in the error message.

### 9.2.9 exit

       exit(code)
          code : Int

The `exit` function terminates `omake` abnormally.

`$(exit <code>)`

The `exit` function takes one integer argument, which is exit code. Non-zero values indicate abnormal termination.

### 9.2.10 defined

       $(defined sequence) : String
          sequence : Sequence

The `defined` function test whether all the variables in the sequence are currently defined. For example, the following code defines the `X` variable if it is not already defined.

        if $(not $(defined X))
           X = a b c
           export

It is acceptable to use qualified names.

        $(defined X.a.b)
        $(defined public.X)

### 9.2.11 defined-env

       $(defined-env sequence) : String
          sequence : String

The `defined-env` function tests whether a variable is defined as part of the process environment.

For example, the following code adds the `-g` compile option if the environment variable `DEBUG` is defined.

    if $(defined-env DEBUG)
        CFLAGS += -g
        export

### 9.2.12 getenv

       $(getenv name) : String
       $(getenv name, default) : String

The `getenv` function gets the value of a variable from the process environment. The function takes one or two arguments.

In the single argument form, an exception is raised if the variable variable is not defined in the environment. In the two-argument form, the second argument is returned as the result if the value is not defined.

For example, the following code defines the variable `X` to be a space-separated list of elements of the `PATH` environment variable if it is defined, and to `/bin /usr/bin` otherwise.

        X = $(split $(PATHSEP), $(getenv PATH, /bin:/usr/bin))

You may also use the alternate form.

         getenv(NAME)
             default

### 9.2.13 setenv

       setenv(name, value)
          name : String
          value : String

The `setenv` function sets the value of a variable in the process environment. Environment variables are scoped like normal variables.

### 9.2.14 unsetenv

       unsetenv(names)
          names : String Array

The `unsetenv` function removes some variable definitions from the process environment. Environment variables are scoped like normal variables.

### 9.2.15 get-registry

       get-registry(hkey, key, field) : String
       get-registry(hkey, key, field, default) : String
           hkey : String
           key : String
           field : String

The `get-registry` function retrieves a string value from the system registry on Win32. On other architectures, there is no registry.

The `hive` (I think that is the right word), indicates which part of the registry to use. It should be one of the following values.

- `HKEY_CLASSES_ROOT`
- `HKEY_CURRENT_CONFIG`
- `HKEY_CURRENT_USER`
- `HKEY_LOCAL_MACHINE`
- `HKEY_USERS`

Refer to the Microsoft documentation if you want to know what these mean.

The `key` is the field you want to get from the registry. It should have a form like `A\B\C` (if you use forward slashes, they will be converted to backslashes). The field is the sub-field of the key.

In the 4-argument form, the `default` is returned on failure. You may also use the alternate form.

        get-registry(hkey, key, field)
           default

### 9.2.16 getvar

       $(getvar name) : String

The `getvar` function gets the value of a variable.

An exception is raised if the variable variable is not defined.

For example, the following code defines X to be the string abc.

        NAME = foo
        foo_1 = abc
        X = $(getvar $(NAME)_1)

It is acceptable to use qualified names.

        $(getvar X.a.b)

### 9.2.17 setvar

       setvar(name, value)
          name : String
          value : String

The `setvar` function defines a new variable. For example, the following code defines the variable `X` to be the string `abc`.

       NAME = X
       setvar($(NAME), abc)

It is acceptable to use qualified names.

        setvar(public.X, abc)

## 9.3 Arrays and sequences

### 9.3.1 array

        $(array elements) : Array
           elements : Sequence

The `array` function creates an array from a sequence. If the `<arg>` is a string, the elements of the array are the whitespace-separated elements of the string, respecting quotes.

In addition, array variables can be declared as follows.

        A[] =
           <val1>
           ...
           <valn>

In this case, the elements of the array are exactly `<val1>`, ..., `<valn>`, and whitespace is preserved literally.

### 9.3.2 split

       $(split sep, elements) : Array
          sep : String
          elements : Sequence

The `split` function takes two arguments, a string of separators, and a string argument. The result is an array of elements determined by splitting the elements by all occurrence of the separator in the `elements` sequence.

For example, in the following code, the `X` variable is defined to be the array `/bin /usr/bin /usr/local/bin`.

        PATH = /bin:/usr/bin:/usr/local/bin
        X = $(split :, $(PATH))

The `sep` argument may be omitted. In this case `split` breaks its arguments along the white space. Quotations are not split.

### 9.3.3 concat

       $(concat sep, elements) : String
          sep : String
          elements : Sequence

The `concat` function takes two arguments, a separator string, and a sequence of elements. The result is a string formed by concatenating the elements, placing the separator between adjacent elements.

For example, in the following code, the `X` variable is defined to be the string `foo_x_bar_x_baz`.

        X = foo  bar     baz
        Y = $(concat _x_, $(X))

### 9.3.4 length

       $(length sequence) : Int
          sequence : Sequence

The `length` function returns the number of elements in its argument.

For example, the expression `$(length a b "c d")` evaluates to 3.

### 9.3.5 nth

       $(nth i, sequence) : value
          i : Int
          sequence : Sequence
       raises RuntimeException

The `nth` function returns the nth element of its argument, treated as a list. Counting starts at 0. An exception is raised if the index is not in bounds.

For example, the expression `$(nth 1, a "b c" d)` evaluates to `"b c"`.

### 9.3.6 replace-nth

       $(replace-nth i, sequence, x) : value
          i : Int
          sequence : Sequence
          x : value
       raises RuntimeException

The `replace-nth` function replaces the nth element of its argument with a new value `x`. Counting starts at 0. An exception is raised if the index is not in bounds.

For example, the expression `$(replace-nth 1, a "b c" d, x)` evaluates to `a x d`.

### 9.3.7 nth-hd

       $(nth-hd i, sequence) : value
          i : Int
          sequence : Sequence
       raises RuntimeException

The `nth-hd` function returns the first `i` elements of the sequence. An exception is raised if the sequence is not at least `i` elements long.

For example, the expression `$(nth-hd 2, a "b c" d)` evaluates to `a "b c"`.

### 9.3.8 nth-tl

       $(nth-tl i, sequence) : value
          i : Int
          sequence : Sequence
       raises RuntimeException

The `nth-tl` function skips `i` elements of the sequence and returns the rest. An exception is raised if the sequence is not at least `i` elements long.

For example, the expression `$(nth-tl 1, a "b c" d)` evaluates to `"b c" d`.

### 9.3.9 subrange

       $(subrange off, len, sequent) : value
          off : Int
          len : Int
          sequence : Sequence
       raises RuntimeException

The `subrange` function returns a subrange of the sequence. Counting starts at 0. An exception is raised if the specified range is not in bounds.

For example, the expression `$(subrange 1, 2, a "b c" d e)` evaluates to `"b c" d`.

### 9.3.10 rev

        $(rev sequence) : Sequence
           sequence : Sequence

The `rev` function returns the elements of a sequence in reverse order. For example, the expression `$(rev a "b c" d)` evaluates to `d "b c" a`.

### 9.3.11 join

       $(join sequence1, sequence2) : Sequence
          sequence1 : Sequence
          sequence2 : Sequence

The `join` function joins together the elements of the two sequences. For example, `$(join a b c, .c .cpp .h)` evaluates to `a.c b.cpp c.h`. If the two input sequences have different lengths, the remainder of the longer sequence is copied at the end of the output unmodified.

### 9.3.12 string

       $(string sequence) : String
          sequence : Sequence

The `string` function flattens a sequence into a single string. This is similar to the `concat` function, but the elements are separated by whitespace. The result is treated as a unit; whitespace is significant.

### 9.3.13 string-length

       $(string-length sequence) : Int
          sequence : Sequence

The `string-lenght` returns a length (number of characters) in its argument. If the argument is a sequence, it flattens it, so `$(string-length sequence)` is equivalent to `$(string-length $(string sequence))`.

### 9.3.14 string-escaped, ocaml-escaped, html-escaped, html-pre-escaped, c-escaped, id-escaped

       $(string-escaped sequence) : String Array
       $(ocaml-escaped sequence) : String Array
       $(html-escaped sequence) : String Array
       $(html-pre-escaped sequence) : String Array
       $(c-escaped sequence) : String Array
       $(hex-escaped sequence) : StringArray
          sequence : Array

The `string-escaped` function converts each element of its argument to a string, escaping it, if it contains symbols that are special to OMake. The special characters include `:()\,$'"#` and whitespace. This function can be used in scanner rules to escape file names before printing then to `stdout`.

The `ocaml-escaped` function converts each element of its argument to a string, escaping characters that are special to OCaml.

The `c-escaped` function converts a string to a form that can be used as a string constant in C.

The `id-escaped` function turns a string into an identifier that may be used in OMake.

The `html-escaped` function turns a literal string into a form acceptable as HTML. The `html-pre-escaped` function is similar, but it does not translate newlines into `<br>`.

        println($(string $(string-escaped $"a b" $"y:z")))
        a\ b y\:z

### 9.3.15 decode-uri, encode-uri

        $(decode-uri sequence) : sequence
            sequence : Sequence

These two functions perform URI encoding, where special characters are represented by hexadecimal characters.

        osh> s = $(encode-uri $'a b~c')
        "a+b%7ec"
        osh> decode-uri($s)
        "a b~c"

### 9.3.16 quote

       $(quote sequence) : String
          sequence : Sequence

The `quote` function flattens a sequence into a single string and adds quotes around the string. Inner quotation symbols are escaped.

For example, the expression `$(quote a "b c" d)` evaluates to `"a \"b c\" d"`, and `$(quote abc)` evaluates to `"abc"`.

### 9.3.17 quote-argv

       $(quote-argv sequence) : String
          sequence : Sequence

The `quote-argv` function flattens a sequence into a single string, and adds quotes around the string. The quotation is formed so that a command-line parse can separate the string back into its components.

### 9.3.18 html-string

       $(html-string sequence) : String
          sequence : Sequence

The `html-string` function flattens a sequence into a single string, and escaped special HTML characters. This is similar to the `concat` function, but the elements are separated by whitespace. The result is treated as a unit; whitespace is significant.

### 9.3.19 addsuffix

       $(addsuffix suffix, sequence) : Array
          suffix : String
          sequence : Sequence

The `addsuffix` function adds a suffix to each component of sequence. The number of elements in the array is exactly the same as the number of elements in the sequence.

For example, `$(addsuffix .c, a b "c d")` evaluates to `a.c b.c "c d".c`.

### 9.3.20 mapsuffix

       $(mapsuffix suffix, sequence) : Array
          suffix : value
          sequence : Sequence

The `mapsuffix` function adds a suffix to each component of sequence. It is similar to `addsuffix`, but uses array concatenation instead of string concatenation. The number of elements in the array is twice the number of elements in the sequence.

For example, `$(mapsuffix .c, a b "c d")` evaluates to `a .c b .c "c d" .c`.

### 9.3.21 addsuffixes

       $(addsuffixes suffixes, sequence) : Array
          suffixes : Sequence
          sequence : Sequence

The `addsuffixes` function adds all suffixes in its first argument to each component of a sequence. If `suffixes` has `n` elements, and `sequence` has `m` elements, the the result has `n * m` elements.

For example, the `$(addsuffixes .c .o, a b c)` expressions evaluates to `a.c a.o b.c b.o c.o c.a`.

### 9.3.22 removeprefix

       $(removeprefix prefix, sequence) : Array
          prefix : String
          sequence : Array

The `removeprefix` function removes a prefix from each component of a sequence.

### 9.3.23 removesuffix

       $(removesuffix sequence) : Array
          sequence : String

The `removesuffix` function removes the suffixes from each component of a sequence.

For example, `$(removesuffix a.c b.foo "c d")` expands to `a b "c d"`.

### 9.3.24 replacesuffixes

       $(replacesuffixes old-suffixes, new-suffixes, sequence) : Array
          old-suffixes : Sequence
          new-suffixes : Sequence
          sequence : Sequence

The `replacesuffixes` function modifies the suffix of each component in sequence. The `old-suffixes` and `new-suffixes` sequences should have the same length.

For example, `$(replacesuffixes .h .c, .o .o, a.c b.h c.z)` expands to `a.o b.o c.z`.

### 9.3.25 addprefix

       $(addprefix prefix, sequence) : Array
          prefix : String
          sequence : Sequence

The `addprefix` function adds a prefix to each component of a sequence. The number of element in the result array is exactly the same as the number of elements in the argument sequence.

For example, `$(addprefix foo/, a b "c d")` evaluates to `foo/a foo/b foo/"c d"`.

### 9.3.26 mapprefix

       $(mapprefix prefix, sequence) : Array
          prefix : String
          sequence : Sequence

The `mapprefix` function adds a prefix to each component of a sequence. It is similar to `addprefix`, but array concatenation is used instead of string concatenation. The result array contains twice as many elements as the argument sequence.

For example, `$(mapprefix foo, a b "c d")` expands to `foo a foo b foo "c d"`.

### 9.3.27 add-wrapper

       $(add-wrapper prefix, suffix, sequence) : Array
          prefix : String
          suffix : String
          sequence : Sequence

The `add-wrapper` functions adds both a prefix and a suffix to each component of a sequence. For example, the expression `$(add-wrapper dir/, .c, a b)` evaluates to `dir/a.c dir/b.c`. String concatenation is used. The array result has the same number of elements as the argument sequence.

### 9.3.28 set

       $(set sequence) : Array
          sequence : Sequence

The `set` function sorts a set of string components, eliminating duplicates.

For example, `$(set z y z "m n" w a)` expands to `"m n" a w y z`.

### 9.3.29 mem

       $(mem elem, sequence) : Boolean
          elem : String
          sequence : Sequence

The `mem` function tests for membership in a sequence.

For example, `$(mem "m n", y z "m n" w a)` evaluates to `true`, while `$(mem m n, y z "m n" w a)` evaluates to `false`.

### 9.3.30 intersection

       $(intersection sequence1, sequence2) : Array
          sequence1 : Sequence
          sequence2 : Sequence

The `intersection` function takes two arguments, treats them as sets of strings, and computes their intersection. The order of the result is undefined, and it may contain duplicates. Use the `set` function to sort the result and eliminate duplicates in the result if desired.

For example, the expression `$(intersection c a b a, b a)` evaluates to `a b a`.

### 9.3.31 intersects

       $(intersects sequence1, sequence2) : Boolean
          sequence1 : Sequence
          sequence2 : Sequence

The `intersects` function tests whether two sets have a non-empty intersection. This is slightly more efficient than computing the intersection and testing whether it is empty.

For example, the expression `$(intersects a b c, d c e)` evaluates to `true`, and `$(intersects a b c a, d e f)` evaluates to `false`.

### 9.3.32 set-diff

       $(set-diff sequence1, sequence2) : Array
          sequence1 : Sequence
          sequence2 : Sequence

The `set-diff` function takes two arguments, treats them as sets of strings, and computes their difference (all the elements of the first set that are not present in the second one). The order of the result is undefined and it may contain duplicates. Use the `set` function to sort the result and eliminate duplicates in the result if desired.

For example, the expression `$(set-diff c a b a e, b a)` evaluates to `c e`.

### 9.3.33 filter

       $(filter patterns, sequence) : Array
          patterns : Sequence
          sequence : Sequence

The `filter` function picks elements from a sequence. The patterns is a non-empty sequence of patterns, each may contain one occurrence of the wildcard `%` character.

For example `$(filter %.h %.o, a.c x.o b.h y.o "hello world".c)` evaluates to `x.o b.h y.o`.

### 9.3.34 filter-out

       $(filter-out patterns, sequence) : Array
          patterns : Sequence
          sequence : Sequence

The `filter-out` function removes elements from a sequence. The patterns is a non-empty sequence of patterns, each may contain one occurrence of the wildcard `%` character.

For example `$(filter-out %.c %.h, a.c x.o b.h y.o "hello world".c)` evaluates to `x.o y.o`.

### 9.3.35 capitalize

       $(capitalize sequence) : Array
          sequence : Sequence

The `capitalize` function capitalizes each word in a sequence. For example, `$(capitalize through the looking Glass)` evaluates to `Through The Looking Glass`.

### 9.3.36 uncapitalize

       $(uncapitalize sequence) : Array
          sequence : Sequence

The `uncapitalize` function uncapitalizes each word in its argument.

For example, `$(uncapitalize through the looking Glass)` evaluates to `through the looking glass`.

### 9.3.37 uppercase

       $(uppercase sequence) : Array
          sequence : Sequence

The `uppercase` function converts each word in a sequence to uppercase. For example, `$(uppercase through the looking Glass)` evaluates to `THROUGH THE LOOKING GLASS`.

### 9.3.38 lowercase

       $(lowercase sequence) : Array
          sequence : Sequence

The `lowercase` function reduces each word in its argument to lowercase.

For example, `$(lowercase through tHe looking Glass)` evaluates to `through the looking glass`.

### 9.3.39 system

       system(s)
          s : Sequence

The `system` function is used to evaluate a shell expression. This function is used internally by `omake` to evaluate shell commands.

For example, the following program is equivalent to the expression `system(ls foo)`.

       ls foo

### 9.3.40 shell

       $(shell command) : Array
       $(shella command) : Array
       $(shell-code command) : Int
          command : Sequence

The `shell` function evaluates a command using the command shell, and returns the whitespace-separated words of the standard output as the result.

The `shella` function acts similarly, but it returns the lines as separate items in the array.

The `shell-code` function returns the exit code. The output is not diverted.

For example, if the current directory contains the files `OMakeroot`, `OMakefile`, and `hello.c`, then `$(shell ls)` evaluates to `hello.c OMakefile OMakeroot` (on a Unix system).

### 9.3.41 export

The `export` function allows one to capture the current environment in a variable.

For example, the following code:

    A = 1
    B = 1
    C = 1
    SAVE_ENV = $(export A B)
    A = 2
    B = 2
    C = 2
    export $(SAVE_ENV)
    println($A $B $C)

will print `1 1 2`.

The arguments to this function are interpreted the exact same way as the arguments to the `export` special form (see Section 6.3).

### 9.3.42 while

       while <test>
          <body>

–or–

        while <test>
        case <test1>
           <body1>
        ...
        case <testn>
           <bodyn>
        default
           <bodyd>

The loop is executed while the test is true. In the first form, the `<body>` is executed on every loop iteration. In the second form, the body `<bodyI>` is selected, as the first case where the test `<testI>` is true. If none apply, the optional default case is evaluated. If no cases are true, the loop exits. The environment is automatically exported.

Examples.

Iterate for `i` from `0` to `9`.

        i = 0
        while $(lt $i, 10)
           echo $i
           i = $(add $i, 1)

The following example is equivalent.

       i = 0
       while true
       case $(lt $i, 10)
          echo $i
          i = $(add $i, 1)

The following example is similar, but some special cases are printed. value is printed.

        i = 0
        while $(lt $i, 10)
        case $(equal $i, 0)
           echo zero
        case $(equal $i, 1)
           echo one
        default
           echo $i

The `break` function can be used to break out of the `while` loop early.

### 9.3.43 break

       break

Terminate execution of the innermost loop, returning the current state.

### 9.3.44 random, random-init

        random-init(i)
            i : Int
        random() : Int

Produce a random number. The numbers are pseudo-random, and are not cryptographically secure.

The generator is initialized form semi-random system data. Subsequent runs should produce different results. The `rando-init` function can be used to return the generator to a known state.

## 9.4 Arithmetic

### 9.4.1 int

The `int` function can be used to create integers. It returns an `Int` object.

`$(int 17)`.

### 9.4.2 float

The `float` function can be used to create floating-point numbers. It returns a `Float` object.

`$(float 3.1415926)`.

### 9.4.3 Basic arithmetic

The following functions can be used to perform basic arithmetic.

- `$(neg <numbers>)`: arithmetic inverse
- `$(add <numbers>)`: addition.
- `$(sub <numbers>)`: subtraction.
- `$(mul <numbers>)`: multiplication.
- `$(div <numbers>)`: division.
- `$(mod <numbers>)`: remainder.
- `$(lnot <numbers>)`: bitwise inverse.
- `$(land <numbers>)`: bitwise and.
- `$(lor <numbers>)`: bitwise or.
- `$(lxor <numbers>)`: bitwise exclusive-or.
- `$(lsl <numbers>)`: logical shift left.
- `$(lsr <numbers>)`: logical shift right.
- `$(asr <numbers>)`: arithmetic shift right.
- `$(min <numbers>)`: smallest element.
- `$(max <numbers>)`: largest element.

### 9.4.4 Comparisons

The following functions can be used to perform numerical comparisons.

- `$(lt <numbers>)`: less then.
- `$(le <numbers>)`: no more than.
- `$(eq <numbers>)`: equal.
- `$(ge <numbers>)`: no less than.
- `$(gt <numbers>)`: greater than.
- `$(ult <numbers>)`: unsigned less than.
- `$(ule <numbers>)`: unsigned greater than.
- `$(uge <numbers>)`: unsigned greater than or equal.
- `$(ugt <numbers>)`: unsigned greater than.

## 9.5 First-class functions

### 9.5.1 fun

The `fun` form introduces anonymous functions.

`$(fun <v1>, ..., <vn>, <body>)`

The last argument is the body of the function. The other arguments are the parameter names.

The three following definitions are equivalent.

        F(X, Y) =
           return($(addsuffix $(Y), $(X)))

        F = $(fun X, Y, $(addsuffix $(Y), $(X)))

        F =
           fun(X, Y)
              value $(addsuffix $(Y), $(X))

### 9.5.2 apply

The `apply` operator is used to apply a function.

`$(apply <fun>, <args>)`

Suppose we have the following function definition.

        F(X, Y) =
           return($(addsuffix $(Y), $(X)))

The the two expressions below are equivalent.

        X = F(a b c, .c)
        X = $(apply $(F), a b c, .c)

### 9.5.3 applya

The `applya` operator is used to apply a function to an array of arguments.

`$(applya <fun>, <args>)`

For example, in the following program, the value of `Z` is `file.c`.

        F(X, Y) =
           return($(addsuffix $(Y), $(X)))
        args[] =
           file
           .c
        Z = $(applya $(F), $(args))

### 9.5.4 create-map, create-lazy-map

The `create-map` is a simplified form for creating `Map` objects. The `create-map` function takes an even number of arguments that specify key/value pairs. For example, the following values are equivalent.

        X = $(create-map name1, xxx, name2, yyy)

        X. =
            extends $(Map)
            $|name1| = xxx
            $|name2| = yyy

The `create-lazy-map` function is similar, but the values are computed lazily. The following two definitions are equivalent.

        Y = $(create-lazy-map name1, $(xxx), name2, $(yyy))

        Y. =
            extends $(Map)
            $|name1| = $`(xxx)
            $|name2| = $`(yyy)

The `create-lazy-map` function is used in rule construction.

## 9.6 Iteration and mapping

### 9.6.1 foreach

The `foreach` function maps a function over a sequence.

        $(foreach <fun>, <args>)

        foreach(<var>, <args>)
           <body>

For example, the following program defines the variable `X` as an array `a.c b.c c.c`.

        X =
           foreach(x, a b c)
              value $(x).c

        # Equivalent expression
        X = $(foreach $(fun x, $(x).c), abc)

There is also an abbreviated syntax.

The `export` form can also be used in a `foreach` body. The final value of `X` is `a.c b.c c.c`.

        X =
        foreach(x, a b c)
           X += $(x).c
           export

The `break` function can be used to break out of the loop early.

## 9.7 Boolean tests

### 9.7.1 sequence-forall

The `forall` function tests whether a predicate halds for each element of a sequence.

        $(sequence-forall <fun>, <args>)

        sequence-forall(<var> => ..., <args>)
           <body>

### 9.7.2 sequence-exists

The `exists` function tests whether a predicate holds for some element of a sequence.

        $(sequence-exists <fun>, <args>)

        sequence-exists(<var> => ..., <args>)
           <body>

### 9.7.3 sequence-sort

The `sort` function sorts the elements in an array, given a comparison function. Given two elements (x, y), the comparison should return a negative number if x < y; a positive number if x > y; and 0 if x = y.

        $(sequence-sort <fun>, <args>)

        sort(<var>, <var> => ..., <args>)
           <body>

### 9.7.4 compare

The `compare` function compares two values (x, y) generically returning a negative number if x < y; a positive number if x > y; and 0 if x = y.

        $(compare x, y) : Int

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