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occam is a concurrent programming language that builds on the communicating sequential processes (CSP) process algebra,〔 INMOS document 72 occ 45 03〕 and shares many of its features. It is named after William of Ockham of Occam's Razor fame. occam is an imperative procedural language (such as Pascal). It was developed by David May and others at INMOS, advised by Tony Hoare, as the native programming language for their transputer microprocessors, but implementations for other platforms are available. The most widely known version is occam 2; its programming manual was written by Steven Ericsson-Zenith and others at INMOS. ==Overview== In the following examples indentation and formatting are critical for parsing the code: expressions are terminated by the end of the line, lists of expressions need to be on the same level of indentation. This feature, named the off-side rule, is also found in other languages such as Haskell and Python. Communication between processes work through named ''channels''. One process outputs data to a channel via "!" while another one inputs data with "?". Input and output can not proceed until the other end is ready to accept or offer data. (In the "not proceeding" case it is often said that the process "blocks" on the channel. However, the program will neither spin nor poll; therefore terms like "wait", "hang" or "yield" may also convey the behaviour - also in the light of the fact that it will not "block" other independent processes from running.) Examples (c is a variable): keyboard ? c screen ! c SEQ introduces a list of expressions that are evaluated sequentially. This is not implicit as it is in most other programming languages. Example: SEQ x := x + 1 y := x * x PAR begins a list of expressions that may be evaluated concurrently. Example: PAR p() q() ALT specifies a list of ''guarded'' commands. The ''guards'' are a combination of a boolean condition and an input expression (both optional). Each guard for which the condition is true and the input channel is ready is successful. One of the successful alternatives is selected for execution. Example: ALT count1 < 100 & c1 ? data SEQ count1 := count1 + 1 merged ! data count2 < 100 & c2 ? data SEQ count2 := count2 + 1 merged ! data status ? request SEQ out ! count1 out ! count2 This will read data from channels c1 or c2 (whichever is ready) and pass it into a merged channel. If countN reaches 100, reads from the corresponding channel will be disabled. A request on the status channel is answered by outputting the counts to out. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Occam (programming language)」の詳細全文を読む スポンサード リンク
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