Braces in GNU APL

Question

I am using GNU APL 1.1 (svn 4460) on Linux 2.6.32 and I have some problems with function definitions.

This snippet works as expected:

∇R←ODD N
R←2|N
∇

(ODD L)/L←⍳10

But when I try this

{2|⍵} 5

or this

ODD←{2|⍵}

I get a syntax error. The same snippets run fine here.

I am a complete beginner to APL. Could anyone explain me what causes this syntax error?

Answer 1

You first example uses conventional APL "del" notation to define a function. The second two examples use direct definition (commonly known as dfns - pronounced dee-funs) which is an extension by Dyalog APL, and obviously does not run in the interpreter you are using. The ease of defining functions this way is a great advantage.

Answer 2

The dfns (function fragment in curly braces) syntax is not supported by all APLs. If it's not supported, expect a syntax error or nonce error.

To my knowledge, only Dyalog APL and NGN APL (see http://ngn.github.io/apl/web/) support it.

Sharp APL had a direct definition feature but the syntax was rather different.

NGN APL does not support legacy function definition, only dfns.

Answer 3

GNU APL has now a support for such dfns; you can try it by compiling it from the subversion repository or wait for the release 1.3.