Learning APL

This tutorial aims to teach some of the basics of the APL language.

It is adapted from an original version written to accompany MicroAPL's APLX interpreter which is available in PDF form.

The present version has been slightly modified so that examples should work with a number of APLs, including:

• APLX from MicroAPL

• Dyalog APL

• APL2 from IBM

• APL+Win from APL2000

• NARS2000 , an Open Source APL. See also Nars2000

The core APL language is similar in all these products, although each vendor has added proprietory extensions. Where code is specific to a particular APL interpreter it will usually be indicated in the text.

Once you're familiar with the material covered here, you might also want to check out Further Topics in APL which covers some more advanced topics.

Trying APL

The APL tutorial will be most effective if you actually try the example code in an APL interpreter. Several vendors provide free or low cost evaluation licenses:

To download a time-limited evaluation copy of APLX for Windows, Macintosh or Linux, visit MicroAPL's Download page. You can also download an older Linux version which is free for personal use.

To apply for a free educational license, or a cheap (£50/€75) non-commercial copy of Dyalog APL visit Dyalog's Download zone

NARS2000, an Open Source APL, does not compete against the commercially available APL implementations, but it is a fully-fledged APL implmentation. Apart from the last chapter (OO) you can do everything mentioned in this tutorial with NARS2000.

Installing the APL font

To display the material in this tutorial properly, you need to ensure that (a) your browser can correctly handle Unicode (UTF-8) encoding, and (b) that you have a suitable APL Unicode font installed on your system. Note that non-Unicode APL fonts like "Dyalog Std" or "Causeway" won't work!

Most modern Browsers (such as Internet Explorer 6 or later, Firefox v2 or later, Safari v3 or later) should be fine. However, we have found problems using Firefox v2 on the Macintosh (the Windows version is OK, and Firefox v3 on the Macintosh is OK).

APL code on this Wiki is encoded using Unicode UTF-8. It should display correctly provided you have at least one of these APL fonts installed on your system:

• MicroAPL's APLX Upright Unicode font (http://www.microapl.co.uk/download/aplx_unicode.ttf). If you have installed a desktop version of APLX (full or evaluation copy), you will have this font installed already.

• Adrian Smith's APL385 Unicode font (http://www.vector.org.uk/resource/apl385.ttf)

• IBM's "Courier APL2" font which comes with APL2.
• Phil Chastney's "SiMPL" font.

• Phil Chastney's "SiMPL medium" font which can be downloaded from the AplCharacters page. NARS2000 is using this font.

The fonts are listed in the order in which the APL wiki tries to make use of them. Of course this has an impact only if you have installed more than one font.

If you don't have either of these fonts installed, the Wiki's style sheets are set to fall back on Microsoft's Arial font. Some versions of this font (e.g. the "Arial Unicode MS" version which ships with the international support component of MS Office) do have the APL characters, but it is not a monospaced font. This means that code samples will display the correct characters, but may not be aligned correctly.

If you do not have either of the APL fonts listed nor a suitable version of Microsoft's Arial font, APL characters will not display properly.

Here's a sample of text which should display in the APL font:

    X ← 3 3⍴÷⍳9 ⋄ Y ← DATA[⍋DATA] ⍝ A comment

It should appear in your browser something like this:

(this is a picture, not text; it will always display APL chars)

If it looks more like this then you do not have the APL font installed:

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