MARPLE for Dyalog Users¶

If you know Dyalog APL, you already know most of MARPLE. This page highlights the differences.

What's the same¶

Most of what you type daily works identically:

All scalar functions with the same glyphs and semantics
⍴, ⍳, ,, ⌽, ⊖, ⍉, ↑, ↓, ∈, ⍋, ⍒ — same behaviour
Reduce /, scan \, first-axis ⌿ ⍀
Outer product ∘.f, inner product f.g
Bracket indexing M[i;j] (including indexed assignment)
Dfn syntax {⍺ + ⍵} with guards, recursion (∇), default ⍺
Dop syntax {⍺⍺/⍵} with ⍺⍺ and ⍵⍵
System commands )save, )load, )fns, )vars, )off

What's different¶

No nested arrays¶

This is the big one. MARPLE arrays are flat — every element is a scalar (number or character). There is no ⊂ (enclose), no ⊃ (disclose/first), no ≡ (depth), no ¨ (each), no ⍤ as "atop", and no arrays of arrays.

If MARPLE eventually adds arrays-of-arrays, it will follow Iverson's Dictionary boxing model (explicit < and >), not APL2's implicit nesting. This is the model used by J.

No tradfns or tradops¶

There are no ∇-header function definitions, no line numbers, no labels, no → (branch), no Del editor. Dfns and dops are the only way to define functions and operators.

No control structures¶

No :If, :For, :While, :Select. Use guards in dfns and recursion instead.

Bracket-axis is deprecated¶

Instead of +/[1]M, use (+/⍤¯1)M or +⌿M. The rank operator replaces bracket-axis for user-defined functions, which bracket-axis can't handle.

Index origin defaults to 1¶

Same as Dyalog's default, but worth noting. ⎕IO is supported.

What's new¶

Rank operator (`⍤`)¶

MARPLE includes the rank operator, which Dyalog also has (since version 14.0). If you already use it in Dyalog, it works identically. If you've been avoiding it, now's a good time to learn — see the rank operator tutorial.

From function (`⌷`)¶

Dyalog has ⌷ (squad indexing), and MARPLE's From works similarly for simple leading-axis selection. The difference: in MARPLE, ⌷ is the preferred indexing mechanism, designed to compose with rank. See Indexing with From.

Namespaces via directories¶

Instead of Dyalog's ⎕NS objects, MARPLE maps namespaces to subdirectories in the workspace. utils:trim calls the trim function in the utils/ subdirectory. The system workspace $: provides the standard library.

I-beam as Python FFI¶

⌶ in MARPLE is an operator that calls Python functions, not a system service dispatcher. (⌶'module.function') Y calls Python code from APL.

Quick equivalence table¶

Dyalog	MARPLE	Notes
`+/[1]M`	`(+/⍤¯1)M` or `+⌿M`	Rank replaces bracket-axis
`f¨ V`	`f⍤0 ⊢ V`	Rank-0 replaces Each for flat arrays
`⊂ X`	(not available)	No enclosure; boxing planned
`⊃ X`	(not available)	No disclosure
`X ≡ Y`	(not available)	No depth; flat arrays only
`:If` / `:For`	Guards + recursion	No control structures
`∇ fn` header	`fn ← {⍵}`	Dfns only
`⎕NS`	Directory namespaces	`utils:fn` syntax
`85⌶`	`(⌶'mod.fn')`	I-beam is a Python FFI operator