mac←{⎕IO ⎕ML←0 1                    ⍝ Simple macro processor.

    mexp←{                          ⍝ macro expansion.
    ⍝   ⎕←∊¨⍵                       ⍝ uncomment to trace.
        dd(a(b uu))←⍵               ⍝ moving window on token stream.
        a≡'\':⍺ ∇(dd b)uu           ⍝ \ escape next token.
        b≡'=':⍺ ∇ defn ⍵            ⍝ = defn: accumulate.
        a∊⊃⍺:⍺ ∇ dref ⍵             ⍝ ⍺ name: expand.
        a≡'(':⍺ ∇ ⍺ ∇ dd(b uu)      ⍝ ( new block: expand.
        a≡')':dd(b uu)              ⍝ ) end of block: done.
        ⍺ ∇(dd a)(b uu)             ⍝ move token downstream.
    }

    defn{                          ⍝ extension of macro defn table.
        dd(name(eq uu))←⍵           ⍝ name from token stream.
        val uuu←⍺ body'('uu         ⍝ macro body.
        (⍺,⍨∘⊂¨name val)⍺⍺ dd uuu   ⍝ extended association vectors.
    }

    body←{                          ⍝ macro body.
        dd(a(b uu))←⍵               ⍝ next tokens and remainder.
        a∊⊃⍺:⍺ ∇ dref dd(a(b uu))   ⍝ expand name at defn time.
        a∊' )',nl:dd(b uu)          ⍝ end of macro body: done.
        a≡'\':⍺ ∇(dd b)uu           ⍝ escape next token.
        a≡'(':⍺ ∇ ⍺ mexp dd(b uu)   ⍝ inner block:
        ⍺ ∇(dd a)(b uu)             ⍝ a-extended word.
    }

    dref{                          ⍝ name replaced with its definition.
        names vals←⍺                ⍝ association vectors.
        dd(name uu)←⍵               ⍝ name and remaining tokens.
        val(namesname)vals       ⍝ value corresponding to name.
        ddd ndd number 1           ⍝ numeric parameter from downstream.
        ⍺ ⍺⍺ ddd(val(n copy)uu)     ⍝ expanded macro insert.
    }

    number←{                        ⍝ number for / replication.
        dd d←⍺                      ⍝ remaining and least sig. digits.
        ~d∊⎕D:⍺ 0                   ⍝ not a number: 0.
        ddd ndd ∇ ⍵×10             ⍝ value of digits to left.
        ddd(n+⍵×⎕D⍳d)               ⍝ downstream tokens and number.
    }

    copy{                          ⍝ splice macro body upstream.
        ⍺≡'(':⍵                     ⍝ start of value: done.
        vv v←⍺                      ⍝ v is next value token.
        v≡'/':vv ∇↑list ⍺⍺ 1/⍵      ⍝ / replicate token upstream.
        vvv ⍵                    ⍝ copy token upstream.
    }

    nl←⎕UCS 13                      ⍝ newline char.
    list←{⍺ ⍵}/                     ⍝ list from vector.

    1↓¯2↓∊''⍬ mexp'(',list ⍵,')'    ⍝ macro-expanded code.
}
code_colours

test script

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