# HOPL

The **History of Programming Languages conference** is held by SIGPLAN to discuss and record the history of programming language development. It is notable to APL historians because of the very detailed papers presented at the 1978 and 2020 conferences. ACM SIGPLAN is the Special Interest Group on Programming Languages; while SIGAPL is a chapter of SIGPLAN, it is not directly associated with HOPL.

To date, there have been four HOPL conferences: they are held infrequently, but with increasing frequency. The first, in 1978, featured a presentation by Ken Iverson and Adin Falkoff on APL^{[1]}. The fourth conference, in 2020, features an APL presentation again, this time by Morten Kromberg and Roger Hui^{[2]}.

Conference years appear to be given by the expression:

```
1962++\⌽⍳16
1978 1993 2007 2020 2032 2043 2053 2062 2070 2077 2083 2088 2092 2095 2097 2098
```

### HOPL IV conference badge

One of the conference badges for HOPL IV features an APL expression or `÷+/÷(E≠0)/E`

which computes multiple aspects of electrical circuits:

`÷` |
`+/` |
`÷` |
`(E≠0)` |
`/` |
`E`
| |

`E` |
is a vector of real numeric values | |||||

`(E≠0)` |
produces a Boolean mask indicating which components have a non-zero value | |||||

`(E≠0)` |
`/` |
`E` |
uses the mask to filter the components, thus removing the zeros | |||

`÷` |
finds the reciprocal of those | |||||

`+/` |
sums them up | |||||

`÷` |
computes the reciprocal of that |

The equivalent mathematical formula would be quite involved:

## External links

## References

- ↑ Falkoff, A.D., and K.E. Iverson,
*The Evolution of APL*(web), ACM SIGPLAN Notices, Volume 13, Number 8, 1978-08. - ↑ HOPL 2020 conference abstracts.

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