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The REPL

MARPLE provides two interactive environments: a terminal REPL and a web REPL.

Terminal REPL

marple          # launch the terminal REPL

      )off      ⍝ exit the REPL

You can also exit with Ctrl+D (Unix/macOS) or Ctrl+Z then Enter (Windows).

Typing APL glyphs in the terminal

In the terminal REPL, type APL characters using backtick sequences: press ` followed by a letter or symbol.

You type You get Name
`r ⍴ Rho (shape/reshape)
`i ⍳ Iota (index generator)
`l ← Assignment
`J ⍤ Rank operator
`I ⌷ From (squad)

The translation happens live — the APL character appears immediately.

Tip

A complete glyph reference card is available at Glyph Input.

Alternatively, if you have a Dyalog APL keyboard layout installed (e.g. via setxkbmap with grp:win_switch), you can use the Win key to type APL glyphs directly.

Web REPL

python -m marple.web.server          # start on port 8888
python -m marple.web.server --port 9000  # custom port

Open http://localhost:8888/ in your browser. The web REPL provides:

  • Language bar — clickable APL glyphs above the input area. Click a glyph to insert it. Hover for name and description.
  • Workspace panel — sidebar showing defined variables (with shapes) and functions. Click a name to insert it into the input.
  • Session history — up/down arrow keys cycle through previously entered expressions.
  • Multi-line input — Shift+Enter adds a newline; Enter submits. Newlines are converted to ⋄ (diamond) for execution.

The web REPL is accessible from other machines on the same network — useful for running MARPLE on a Raspberry Pi and programming it from your workstation.

The prompt

The MARPLE prompt is six spaces, following APL tradition:

      2 + 3
5
      ⍳5
1 2 3 4 5

Comments

Everything after ⍝ (lamp) on a line is a comment:

      2 + 3  ⍝ this is a comment
5

System commands

System commands start with ) and work in both the terminal and web REPLs.

Command Description
)off Exit the REPL (terminal only)
)clear Clear the workspace
)fns List defined functions
)vars List defined variables
)save Save the current workspace
)load name Load a saved workspace
)lib List available workspaces
)wsid Show the current workspace name
)wsid name Set the workspace name

See System Commands for full details.