Category:ALGOL 68: Difference between revisions
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m (→Coercion (casting): clarify the difference between soft, week, meek, firm and strong typing.) |
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coercions are available at a particular point in the program. These contexts are: |
coercions are available at a particular point in the program. These contexts are: |
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{|class="wikitable" |
{|class="wikitable" |
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!rowspan=2| N<br> |
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! Context name !! Context location !! Coercions available in this context!! Coercion examples |
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a<br> |
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m<br> |
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e |
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!rowspan=2| Context location |
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!colspan=5| Coercions available in this context |
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!rowspan=2| Coercion examples |
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|bgcolor=eeeeee|Soft |
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!soft |
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|bgcolor=dddddd|Meek |
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|| The LHS of assignments, as "~" in: <lang algol68>~ := ...</lang> |
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|bgcolor=cccccc|Weak |
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|| deproceduring |
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|bgcolor=bbbbbb|Firm |
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|bgcolor=aaaaaa|Strong |
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* deproceduring of: <lang algol68>PROC REAL random: e.g. random</lang> |
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|- |
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!weak |
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* Primaries of slices, as in "~" in: <lang algol68>~[1:99]</lang> |
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* Secondaries of selections, as "~" in: <lang algol68>value OF ~</lang> |
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|| all '''soft''' then weak dereferencing |
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<lang algol68>REF BOOL to REF BOOL |
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REF REF INT to REF INT |
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REF REF REF REAL to REF REAL |
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REF REF REF REF STRUCT to REF STRUCT</lang> |
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|- |
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!meek |
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* Trimscripts (yielding INT) |
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* Enquiries: e.g. as "~" in the following<lang algol68>IF ~ THEN ... FI</lang> and <lang algol68>FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc</lang> |
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* Primaries of calls (e.g. sin in sin(x)) |
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|| all '''weak''' then dereferencing |
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<lang algol68>REF REF BOOL to BOOL |
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REF REF REF INT to INT</lang> |
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|- |
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!firm |
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*Operands of formulas as "~" in:<lang algol68>OP: ~ * ~</lang> |
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*Parameters of transput calls |
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|| all '''meek''' then uniting |
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|| e.g. <lang algol68>UNION(INT,REAL) var := 1</lang> |
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|- |
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!S<br> |
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!strong |
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t<br> |
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r<br> |
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o<br> |
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n<br> |
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g |
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||Right hand side of: |
||Right hand side of: |
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* Identity-declarations, as "~" in: <lang algol68>REAL x = ~</lang> |
* Identity-declarations, as "~" in: <lang algol68>REAL x = ~</lang> |
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* All parts (but one) of a balanced clause |
* All parts (but one) of a balanced clause |
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* One side of an identity relation, as "~" in: <lang algol68> ~ IS ~</lang> |
* One side of an identity relation, as "~" in: <lang algol68> ~ IS ~</lang> |
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|bgcolor=EEEEEE rowspan=4 width="50px"| deproc- eduring |
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|| all '''firm''' then widening, rowing and voiding |
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|bgcolor=DDDDDD rowspan=3 width="50px"| all '''soft''' then weak deref- erencing |
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||Widening occures if there is no loss of precision. For example: An INT will be coerced to a REAL, and a REAL will be coerced to a LONG REAL. But not vice-versa. Examples: |
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|bgcolor=CCCCCC rowspan=2 width="50px"| all '''weak''' then deref- erencing |
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|bgcolor=BBBBBB rowspan=1 width="50px"| all '''meek''' then uniting |
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|bgcolor=AAAAAA width="50px"| all '''firm''' then widening, rowing and voiding |
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|colspan=1 bgcolor=AAAAAA| |
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Widening occurs if there is no loss of precision. For example: An INT will be coerced to a REAL, and a REAL will be coerced to a LONG REAL. But not vice-versa. Examples: |
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<lang algol68>INT to LONG INT |
<lang algol68>INT to LONG INT |
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INT to REAL |
INT to REAL |
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BITS to []BOOL |
BITS to []BOOL |
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BYTES to STRING</lang> |
BYTES to STRING</lang> |
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A variable can also be coerced (rowed) to an array of length 1. |
A variable can also be coerced (rowed) to an array of length 1. |
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For example: |
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<lang algol68>INT to [1]INT |
<lang algol68>INT to [1]INT |
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REAL to [1]REAL</lang> etc |
REAL to [1]REAL</lang> etc |
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|- |
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!F<br> |
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i<br> |
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r<br> |
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m |
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*Operands of formulas as "~" in:<lang algol68>OP: ~ * ~</lang> |
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*Parameters of transput calls |
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|colspan=3 bgcolor=BBBBBB| Example: |
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<lang algol68>UNION(INT,REAL) var := 1</lang> |
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|- |
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!M<br> |
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e<br> |
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e<br> |
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k |
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* Trimscripts (yielding INT) |
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* Enquiries: e.g. as "~" in the following |
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<lang algol68>IF ~ THEN ... FI</lang> and |
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<lang algol68>FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc</lang> |
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* Primaries of calls (e.g. sin in sin(x)) |
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|colspan=4 bgcolor=CCCCCC|Examples: |
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<lang algol68>REF REF BOOL to BOOL |
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REF REF REF INT to INT</lang> |
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|- |
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!W<br> |
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e<br> |
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a<br> |
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k |
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* Primaries of slices, as in "~" in: <lang algol68>~[1:99]</lang> |
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* Secondaries of selections, as "~" in: <lang algol68>value OF ~</lang> |
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|colspan=5 bgcolor=DDDDDD|Examples: |
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<lang algol68>REF BOOL to REF BOOL |
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REF REF INT to REF INT |
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REF REF REF REAL to REF REAL |
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REF REF REF REF STRUCT to REF STRUCT</lang> |
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|- |
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!S<br> |
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o<br> |
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f<br> |
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t |
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|| The LHS of assignments, as "~" in: <lang algol68>~ := ...</lang> |
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|colspan=6 bgcolor=EEEEEE| Example: |
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* deproceduring of: <lang algol68>PROC REAL random: e.g. random</lang> |
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For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]]. |
For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]]. |
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