Category:ALGOL 68: Difference between revisions

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 ALGOL 68 has a hierarchy of contexts which determine which kind of
 coercions are available at a particular point in the program. These contexts are:
+{|class="wikitable"
-* soft - deproceduring
+! Context name !! Coercions applied in this context !! Context location !! Coercion examples
-* weak - dereferencing or deproceduring, yielding a name
+|-
-* meek - dereferencing or deproceduring
+|soft || deproceduring
-* firm - meek, followed by uniting
+|| The LHS of assignments, as in: <lang algol68>:=</lang>
-* strong - firm, followed by widening, rowing or voiding
+||
+* deproceduring of: <lang algol68>PROC REAL random: e.g. random</lang>
-Depending on the context a MODE (type) will be coerced (widened) to another type if there is no loss
+|-
-of precision. For example: An INT will be coerced to a REAL, and a REAL will be
+|weak || all ''soft'' above then weak dereferencing
-coerced to a LONG REAL.  But not vice-versa.  Examples:
+||
-* INT to REAL
+* Primaries of slices
-* REAL to COMPL
+* Secondaries of selections, as in: <lang algol68>OF</lang>
-* BITS to []BOOL
+||
-* BYTES to STRING
+<lang algol68>REF REF REF INT to REF INT</lang>
+|-
+|meek
+|| all ''weak'' above then dereferencing
+||
+* Trimscripts (yielding INT)
+* Enquiries: e.g. "~" in the following<lang algol68>IF ~ THEN ... FI</lang> and <lang algol68>FROM ~ BY ~ TO ~ WHILE ~ DO ... OD etc</lang>
+* Primaries of calls (e.g. sin in sin(x))
+||
+<lang algol68>REF REF REF REAL to REAL</lang>
+|-
+|firm || all ''meek'' then uniting
+||
+*Operands of formulas
+*Parameters of transput calls
+|| e.g. <lang algol68>UNION(INT,REAL) var := 1</lang>
+|-
+||strong
+|| all ''firm'' followed by widening, rowing or voiding
+||Right hand side of:
+* Identity-declarations :=:
+* Initialisations
+Also:
+* Actual-parameters of calls
+* Enclosed clauses of casts
+* Units of routine-texts
+* Statements yielding VOID
+* All parts (but one) of a balanced clause
+* One side of an identity relation
+||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:
+<lang algol68>INT to LONG INT
+INT to REAL
+REAL to COMPL
+BITS to []BOOL
+BYTES to STRING</lang>
 A variable can also be coerced (rowed) to an array of length 1.  For example:
-* INT to [1]INT
+<lang algol68>INT to [1]INT
-* REAL to [1]REAL etc
+REAL to [1]REAL</lang> etc
+|}
-Pointers are followed (dereferenced), For example:
+For more details about Primaries and Secondaries refer to [[Operator_precedence#ALGOL_68|Operator precedence]].
-* REF REF REAL to REAL
 == Code Specimen ==
 {{language programming paradigm|Concurrent}}