WordNet

grow out of, have roots in, originate in; "The increase in the national debt stems from the last war"
stop the flow of a liquid; "staunch the blood flow"; "stem the tide" (同)stanch, staunch, halt
remove the stem from; "for automatic natural language processing, the words must be stemmed"
the tube of a tobacco pipe
cause to point inward; "stem your skis"
chance to be or do something, without intention or causation; "I happen to have just what you need!"
happen, occur, or be the case in the course of events or by chance; "It happens that today is my birthday"; "These things befell" (Santayana) (同)befall, bechance
come to pass; "What is happening?"; "The meeting took place off without an incidence"; "Nothing occurred that seemed important" (同)hap, go_on, pass_off, occur, pass, fall_out, come_about, take_place
come into being; become reality; "Her dream really materialized" (同)materialize, materialise
pass through the tissue or substance or its pores or interstices, as of gas (同)transpirate
come about, happen, or occur; "Several important events transpired last week"
come to light; become known; "It transpired that she had worked as spy in East Germany"
exude water vapor; "plants transpire"
give off (water) through the skin
begin a trip at a certain point, as of a plane, train, bus, etc.; "The flight originates in Calcutta"
come into existence; take on form or shape; "A new religious movement originated in that country"; "a love that sprang up from friendship"; "the idea for the book grew out of a short story"; "An interesting phenomenon uprose" (同)arise, rise, develop, uprise, spring up, grow
bring into being; "He initiated a new program"; "Start a foundation" (同)initiate, start
result or issue; "A slight unpleasantness arose from this discussion" (同)come_up
rise to ones feet; "The audience got up and applauded" (同)rise, uprise, get_up, stand_up
originate or come into being; "a question arose" (同)come_up, bob up
reach or enter a state, relation, condition, use, or position; "The water came to a boil"; "We came to understand the true meaning of life"; "Their anger came to a boil"; "I came to realize the true meaning of life"; "The shoes came untied"; "come into co
be found or available; "These shoes come in three colors; The furniture comes unassembled"
come to pass; arrive, as in due course; "The first success came three days later"; "It came as a shock"; "Dawn comes early in June"
happen as a result; "Nothing good will come of this"
develop into; "This idea will never amount to anything"; "nothing came of his grandiose plans" (同)add up, amount
be received; "News came in of the massacre in Rwanda" (同)come_in
move toward, travel toward something or somebody or approach something or somebody; "He came singing down the road"; "Come with me to the Casbah"; "come down here!"; "come out of the closet!"; "come into the room" (同)come_up
to be the product or result; "Melons come from a vine"; "Understanding comes from experience" (同)follow
cover a certain distance; "She came a long way"
exist or occur in a certain point in a series; "Next came the student from France"
experience orgasm; "she could not come because she was too upset"
extend or reach; "The water came up to my waist"; "The sleeves come to your knuckles"
have a certain priority; "My family comes first"

PrepTutorEJDIC

(草の)『茎』,(木の)『幹』 / 葉柄,花梗(かこう) / 『茎状のもの』;(杯・グラスの)『脚』,(パイプ・さじの)柄,(時計の)りゅうず / (単語の)語幹,語根 / 船首;船首材 / …‘の'茎(軸)を取り去る,へたをとる / (…から)生じる,(…に)由来する《+『from』+『名』(do『ing』)》
〈流れなど〉‘を'止める / 〈風・水流など〉‘に'逆らって進む,抵抗する / 〈攻撃・反対など〉‘を'くい止める,押さえる
〈でき事が〉『起こる』,発生する,生ずる / 『偶然(たまたま)…する』 / 《『happen』『to』+『名』》〈でき事が〉…に起こる,降りかかる
恐らく
《話》起こる,生ずる(happen) / 〈秘密などが〉もれる,知れる / 〈水分・老廃物などが〉出る,排出される / 〈水分や老廃物など〉‘を'出す,発散する
…‘を'『引き起こす』 / …‘を'『考え出す』,発明する / (…に,…から)『起こる』(begin)《+『in』(『from』)+『名』》 / (人に)始まる《+『with』+『名』〈人〉》
〈問題・事件などが〉『起こる』,現れる / (…から)生じる(result)《+『from』+『名』》 / 《古・詩》起き上がる,立ち上がる / 《英ではまれ》〈霧・煙などが〉立ちのぼる,湧きあがる
〈相手が〉(話し手の方へ)『来る』,やって来る;〈話し手が〉(相手の方へ)『行く』,伺う《+『to』(『into』)+『名』》 / (ある場所に)『着く』,到着する《+『to』+『名』》 / 〈時が〉『到来する』;〈順序が〉くる / (…に)『届く』,達する《+『to』+『名』》 / 〈事が〉(…に)『起こる』,生じる,降りかかる《+『to』+『名』》,(…から)起こる《+『from』(『of』)+『名』》 / 〈物が〉現れる,できる;〈子が〉生まれる / 〈考えなどが〉(人の)心に浮かぶ《+『to』+『名』》 / 〈人が〉(…の)『出身である』,生まれである《+『from』(『of』)+『名』》 / 〈商品などが〉利用できる,手に入る / (ある状態・結果に)『なる』,至る / 《命令形で促したり警告などを表して》さあ,これこれ / 《仮定法現在で,年月・時期などを表す語[句]の前で》…が来ると / 《仮定法現在》〈障害・難関など〉が来ても / 《『come the』+『名』の形で》(…の)ふるまいをする,(…)ぶる
《場所》…『から』 / 《範囲》 / 《時》…『から』 / 《運動・行動などの起点》 / 《範囲》 / 《数量・価格》…『から』 / 《分離・隔たり》…『から』 / 《状態の変化》…『から』 / 《起源・出典・由来・出身》…『から』 / 《原因・理由・根拠》…『から』;…で,によって / 《原料》…『から』 / 《相違・区別》…『と』[『違って』] / 《除去・選択・解放・奮取》…『から』 / 《抑制・妨害》…[すること]『を』《+do『ing』》 / 《副詞・前置詞句・名詞節を伴って,方向》…『から』
『来たるべき』,『次の』 / 《話》前途有望な,今売り出し中の;新進の / (…の)『到来』,接近,致着(arrival)《+『of』+『名』》

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/07/11 00:19:46」(JST)

wiki en

[Wiki en表示]

In computer programming, COMEFROM (or COME FROM) is an obscure control flow structure used in some programming languages, originally as a joke. COMEFROM is roughly the opposite of GOTO in that it can take the execution state from any arbitrary point in code to a COMEFROM statement.

The point in code where the state transfer happens is usually given as a parameter to COMEFROM. Whether the transfer happens before or after the instruction at the specified transfer point depends on the language used. Depending on the language used, multiple COMEFROMs referencing the same departure point may be invalid, be non-deterministic, be executed in some sort of defined priority, or even induce parallel or otherwise concurrent execution as seen in Threaded Intercal.

A simple example of a "COMEFROM x" statement is a label x (which does not need to be physically located anywhere near its corresponding COMEFROM) that acts as a "trap door". When code execution reaches the label, control gets passed to the statement following the COMEFROM. This may also be conditional, passing control only if a condition is satisfied, analogous to a GOTO within an IF statement. The primary difference from GOTO is that GOTO only depends on the local structure of the code, while COMEFROM depends on the global structure – a GOTO transfers control when it reaches a line with a GOTO statement, while COMEFROM requires scanning the entire program or scope to see if any COMEFROM statements are in scope for the line, and then verifying if a condition is hit. The effect of this is primarily to make debugging (and understanding the control flow of the program) extremely difficult, since there is no indication near the line or label in question that control will mysteriously jump to another point of the program – one must scan the entire program to see if any COMEFROM statements reference that line or label.

While COMEFROM is generally considered humorous, similar semantics are obtained with breakpoints in a debugger, where control is transferred when a condition is satisfied. This is possible because the debugger is executing the program and monitoring its global state. Conversely, because debuggers implement the desired behavior, debugger hooks can be used to implement a COMEFROM statement, as in the humorous Python goto module; see below.

History[edit]

COMEFROM was initially seen in lists of joke assembly language instructions (as 'CMFRM'). It was elaborated upon in a Datamation article by R. Lawrence Clark in 1973,^[1] written in response to Edsger Dijkstra's letter Go To Statement Considered Harmful. COMEFROM was eventually implemented in the C-INTERCAL variant of the esoteric programming language INTERCAL along with the even more obscure 'computed COMEFROM'. There were also Fortran proposals for 'assigned COME FROM' and a 'DONT' keyword (to complement the existing 'DO' loop).

On 1 April 2004, Richie Hindle published an implementation of both GOTO and COMEFROM for the Python programming language.^[2] Despite being released on April Fools' Day and not being intended for serious use, the syntax is valid and the implementation fully works.

Practical uses[edit]

Although COMEFROM is syntactically and semantically valid, and capable of replacing GOTO in some programs, it is considerably more difficult to visualise in program design and actually implement in a programming language. The most well known use of a COMEFROM-like construct is setting a breakpoint during debugging. One implementation of FORTRAN included it, under the name "AT", as a debugging aid, with dire warnings against using it in production code. In addition, many modern CPUs have hardware support for breakpoints.

Some elements of aspect-oriented programming have been compared to the COMEFROM statement.^[3]

In some reversible computing assembly languages, the target of a GOTO is always a COMEFROM targeting the GOTO^{[citation needed]}.

Examples[edit]

The following is an example of a program in a hypothetical BASIC dialect with "COMEFROM" instead of "GOTO".

10 COMEFROM 40
20 INPUT "WHAT IS YOUR NAME? "; A$
30 PRINT "HELLO, "; A$
40 REM

The program (hypothetically) works by asking the user for their name, then greeting them with the same name, and continuing all over again. The instruction "REM" on line 40 is simply a NOP — the "COMEFROM" statement on line 10 causes a branch back to that line when execution reaches line 40, regardless of its contents.

A fully runnable example in Python with the joke goto module installed (which uses debugger hooks to control program execution) looks like this:

from goto import comefrom, label
 
comefrom .repeat
name = raw_input('what is your name? ')
if name:
    print "Hello",name
    label .repeat
print "Goodbye!"

This is an implementation in Ruby of the Intercal COME FROM statement.

$come_from_labels = {}
 
def label(l)
    if $come_from_labels[l]
        $come_from_labels[l].call
    end
end
 
def come_from(l)
    callcc do |block|
        $come_from_labels[l] = block
    end
end

Some examples of the debug packet feature of the OS/360 Fortran G compiler:^[4]

Example 1:
 
      INTEGER SOLON, GFAR, EWELL
         .
         .
         .
10    SOLON = GFAR * SQRT(FLOAT(EWELL))
11    IF (SOLON) 40, 50, 60
         .
         .
         .
      DEBUG UNIT(3)
      AT 11
      DISPLAY GFAR, SOLON, EWELL
      END
 
Example 2:
 
      DIMENSION STOCK(1000),OUT(1000)
         .
         .
         .
      DO 30 I=1, 1000
25    STOCK(I)=STOCK(I) - OUT(I)
30    CONTINUE
35    A = B + C
         .
         .
         .
      DEBUG UNIT(3)
      AT 35
      DISPLAY STOCK
      END
 
Example 3:
 
10    A = 1.5
12    L = 1
15    B = A + 1.5
20    DO 22 I = 1,5
         .
         .
         .
22    CONTINUE
25    C = B + 3.16
30    D = C/2
      STOP
         .
         .
         .
      DEBUG UNIT(3), TRACE
C     DEBUG PACKET NUMBER 1
      AT 10
      TRACE ON
C     DEBUG PACKET NUMBER 2
      AT 20
      TRACE OFF
      DO 35 I = 1,3
         .
         .
         .
35    CONTINUE
      TRACE ON
C     DEBUG PACKET NUMBER 3
      AT 30
      TRACE OFF
      END

In example 1, the values of SOLON, GFAR, and EWELL are examined as they were at the completion of statement 10. The AT statement indicates statement 11.

In example 2, all the values of STOCK are displayed when statement 35 is encountered.

In example 3, tracing begins at statement 10, at statement 20, tracing stops while the loop is executed, and resumes after the loop. Tracing stops just before statement 30 is executed.

Hardware implementation[edit]

The SHARC DSP supports a DO..UNTIL instruction, intended for do..while loops, that is essentially a COMEFROM. Example:

    LCNTR=42;
    DO x UNTIL LCE;  /* COMEFROM x, unless the loop counter is zero */
    F12=F0*F4, F8=F8+F12, F0=dm(I0,M3), F4=pm(I8,M9);
    IF NZ dm(I2,M2) = F12;
    IF ZF dm(I2,M2) = F1;
x:  R2 = R3 + 76;   /* the label "x" does not exist in the machine code */

Note that the loop termination condition, here specified as LCE (loop counter expired), can be set to other values including always-true and always-false. With an always-true condition, we have a genuine COMEFROM. The hardware supports up to six simultaneously active COMEFROMs.

A similar feature exists in Microchip dsPIC's for (unnested) loops provided by the 'DO' assembly instruction. Its interruptible and trivial nesting goes up to one level with an additional 5 levels in software.

References[edit]

^ Clarke, Lawrence, "We don't know where to GOTO if we don't know where we've COME FROM. This linguistic innovation lives up to all expectations.", Datamation (article) .
^ Hindle, Richie (1 April 2004), "goto for Python", Entrian .
^ C2:ComeFrom
^ IBM System/360 and System/370 Fortran IV Language, GC28-6515-10, May 1974
^ F. X. Reid, On the Formal Semantics of the COMEFROM Statement. FACS FACTS, Issue 2006-1, pages 18–20, March 2006.

External links[edit]

COMEFROM Information Page
Datamation Article
Joke Assembler Instruction List Including CMFRM
comefrom support for Perl

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