APL

APL began as Kenneth Iverson’s mathematical notation, published in his 1962 book A Programming Language, and was first implemented at IBM as APL\360 in 1966. Every function works on whole arrays, and most are a single glyph, so a sum is +/X, a mean is (+/X)÷≢X, and a program that would be a page of loops elsewhere fits in a few lines. GNU APL has a ⎕MX statistics and matrix function when it is built with GSL, a third-party library; GSL isn’t installed, so ⎕MX isn’t available here. GNU APL is the GNU project’s free interpreter of ISO standard APL with nested arrays. The runner executes each main.apl as a script, and the comments explain every line for readers new to APL.

Quirks

• Expressions run right to left with no operator precedence: 2×3+4 is 14, and 10-5-2 is 7.
• Negative numbers are written with a high minus, ¯3, which is not the - function. ⍕ prints ¯ too, and its fixed-decimal format drops the leading zero (0 6⍕0.94 gives .940000), so each program formats its own output.
• Indexing starts at 1, set by the system variable ⎕IO (index origin).
• In GNU APL a {} function fits on one line, so longer functions use the older ∇ definitions and jump to labels with → to loop.

git clone https://github.com/qnixon/dswithx.git
cd dswithx
python3 harness/run_tests.py --language apl