74 lines
2.3 KiB
Plaintext
74 lines
2.3 KiB
Plaintext
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[[painless-specification]]
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== Painless Language Specification
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Painless uses a Java-style syntax that is similar to Groovy. In fact, most
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Painless scripts are also valid Groovy, and simple Groovy scripts are typically
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valid Painless. This specification assumes you have at least a passing
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familiarity with Java and related languages.
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Painless is essentially a subset of Java with some additional scripting
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language features that make scripts easier to write. However, there are some
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important differences, particularly with the casting model. For more detailed
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conceptual information about the basic constructs that Java and Painless share,
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refer to the corresponding topics in the
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https://docs.oracle.com/javase/specs/jls/se8/html/index.html[Java Language
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Specification].
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Painless scripts are parsed and compiled using the http://www.antlr.org/[ANTLR4]
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and http://asm.ow2.org/[ASM] libraries. Painless scripts are compiled directly
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into Java byte code and executed against a standard Java Virtual Machine. This
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specification uses ANTLR4 grammar notation to describe the allowed syntax.
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However, the actual Painless grammar is more compact than what is shown here.
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[float]
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[[comments]]
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==== Comments
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Painless supports both single-line and multi-line comments. You can include
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comments anywhere within a script.
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Single-line comments are preceded by two slashes: `// comment`. They can be
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placed anywhere on a line. All characters from the two slashes to the end of
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the line are ignored.
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Multi-line comments are preceded by a slash-star `/*` and closed by
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star-slash `*/`. Multi-line comments can start anywhere on a line. All
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characters from the opening `/*` to the closing `*/` are ignored.
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*Examples:*
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[source,Java]
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----
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// single-line comment
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<code> // single-line comment
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/* multi-
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line
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comment */
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<code> /* multi-line
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comment */ <code>
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<code> /* multi-line comment */ <code>
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----
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[float]
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[[keywords]]
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==== Keywords
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Painless reserves the following keywords for built-in language features.
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These keywords cannot be used used in other contexts, such as identifiers.
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[cols="^1,^1,^1,^1,^1"]
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|====
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| if | else | while | do | for
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| in | continue | break | return | new
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| try | catch | throw | this | instanceof
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|====
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include::painless-literals.asciidoc[]
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include::painless-variables.asciidoc[]
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include::painless-types.asciidoc[]
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include::painless-operators.asciidoc[]
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