tokens←{⎕ML←1                           ⍝ Lex of APL src line.
    ⍺←0 ⋄ nv←⍺                          ⍝ numeric vectors as single token.
    alph←{(0≤⎕NC⍪⍵)/⍵}⎕AV~'⍺⍵∇'         ⍝ alphabet for names.
    all←{+/∧\⍺∊⍵}                       ⍝ No. of leading ⍺∊⍵.
    acc←{(⍺,↑/⍵)lex⊃↓/⍵}                ⍝ accumulated tokens.
    lex←{
        0=⍴⍵:⍺ ⋄ hd←⊃⍵                  ⍝ Next char else finished.
        hd=' ':⍺{                       ⍝ White Space.
            size←⍵ all' '
            ⍺ acc size ⍵
        }⍵
        hdalph:⍺{                      ⍝ Name
            size←⍵ all alph,⎕D
            ⍺ acc size ⍵
        }⍵
        hd∊'⎕':⍺{                       ⍝ System Name
            size←1+(1↓⍵)all alphacc size ⍵
        }⍵
        hd='''':⍺{                      ⍝ Char literal
            size←+/∧\{⍵∨¯1⌽⍵}≠\hd=⍵
            ⍺ acc size ⍵
        }⍵
        hd∊⎕D,'¯':⍺{                    ⍝ Numeric literal
            max←⍵ all ⎕D,'.¯EJ',nv/' '  ⍝ numbers with trailing blanks.
            sizemax-+/∧\' '=⌽max↑⍵     ⍝  ..  without trailing blanks.
            ⍺ acc size ⍵
        }⍵
        hd∊'⍺⍵∇:':⍺{                    ⍝ ⍺⍺ or ⍵⍵ or ∇∇ or ::
            size←⍵ all hdacc size ⍵
        }⍵
        hd='⍝':⍺ acc(⍴⍵)⍵               ⍝ Comment
        ⍺ acc 1 ⍵                       ⍝ Single char token.
    }
    (0⍴⊂'')lex,⍵
}
code_colours

test script

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