lua的Chunks和block

reference:

http://www.lua.org/manual/5.3/manual.html

3.3.1 – Blocks

A block is a list of statements, which are executed sequentially:

block ::= {stat}

Lua has empty statements that allow you to separate statements with semicolons, start a block with a semicolon or write two semicolons in sequence:

stat ::= ‘;’

Function calls and assignments can start with an open parenthesis. This possibility leads to an ambiguity in Lua's grammar. Consider the following fragment:

a = b + c
     (print or io.write)('done')

The grammar could see it in two ways:

a = b + c(print or io.write)('done')
     
     a = b + c; (print or io.write)('done')

The current parser always sees such constructions in the first way, interpreting the open parenthesis as the start of the arguments to a call. To avoid this ambiguity, it is a good practice to always precede with a semicolon statements that start with a parenthesis:

;(print or io.write)('done')

A block can be explicitly delimited to produce a single statement:

stat ::= do block end

Explicit blocks are useful to control the scope of variable declarations. Explicit blocks are also sometimes used to add a return statement in the middle of another block (see §3.3.4).

明確的限定一個block表示獨立的語句：do..end 內的部分。

3.3.2 – Chunks

The unit of compilation of Lua is called a chunk. Syntactically, a chunk is simply a block:

chunk ::= block

Lua handles a chunk as the body of an anonymous function with a variable number of arguments (see §3.4.11). As such, chunks can define local variables, receive arguments, and return values. Moreover, such anonymous function is compiled as in the scope of an external local variable called _ENV (see §2.2). The resulting function always has _ENV as its only upvalue, even if it does not use that variable.

A chunk can be stored in a file or in a string inside the host program. To execute a chunk, Lua first loads it, precompiling the chunk's code into instructions for a virtual machine, and then Lua executes the compiled code with an interpreter for the virtual machine.

Chunks can also be precompiled into binary form; see program luac and function string.dump for details. Programs in source and compiled forms are interchangeable; Lua automatically detects the file type and acts accordingly (see load).

Lua編譯的單元稱為Chunk，語法上一個chunk是一個簡單的block。

一個chunk可以是一條語句，一個函數，一個文件。

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