Editing Operator overloading (section)

===1960s===
The [[ALGOL 68]] specification allowed operator overloading.<ref>{{cite web |title=Report on the Algorithmic Language ALGOL 68, Section 10.2.2. |url=https://www.softwarepreservation.org/projects/ALGOL/report/Algol68_revised_report-AB-600dpi.pdf =Barry J. Mailloux |last3=Peck |first3=John E. L. |author-link3=John E. L. Peck |last4=Koster |first4= Cornelis H. A. |author-link4=Cornelis H.A. Koster |access-date=1 April 2007 |date=August 1968  |display-authors=etal}}</ref>

Extract from the ALGOL 68 language specification (page 177) where the overloaded operators ¬, =, ≠, and '''abs''' are defined:

 10.2.2. Operations on Boolean Operands
 a) '''op''' ∨ = ('''bool''' a, b) '''bool''':( a | '''true''' | b );
 b) '''op''' ∧ = ('''bool''' a, b) '''bool''': ( a | b | '''false''' );
 c) '''op''' ¬ = ('''bool''' a) '''bool''': ( a | '''false''' | '''true''' );
 d) '''op''' = = ('''bool''' a, b) '''bool''':( a∧b ) ∨ ( ¬b∧¬a );
 e) '''op''' ≠ = ('''bool''' a, b) '''bool''': ¬(a=b);
 f) '''op''' '''abs''' = ('''bool''' a)'''int''': ( a | 1 | 0 );

Note that no special declaration is needed to ''overload'' an operator, and the programmer is free to create new operators. For dyadic operators their priority compared to other operators can be set:

  '''prio''' '''max''' = 9;
  
  '''op''' '''max''' = ('''int''' a, b) '''int''': ( a>b | a | b );
  '''op''' '''++''' = ( '''ref''' '''int''' a ) '''int''': ( a +:= 1 );