Purple Session Bindings

The boot installs fourteen bindings into the session environment before the prelude loads — the Pink machinery of Part III, made available at the prompt. They fall into four groups.

Sources

Programs as data, exactly as read or spliced at boot:

• pink-poly-src — the contents of lib/pink-forms.naj: the stage-polymorphic evaluator as one expression.
• pink-tie-src — pink-poly-src wrapped with the knot-tying lambda; takes an l pair.
• pink-eval-src — pink-tie-src applied to the identity lift, as source.
• pink-evalc-src — pink-tie-src applied to the real lift, as source.

(car pink-poly-src)
;=> 'let

Evaluators

The same four, animated:

• pink-poly — the evaluator awaiting its own recursion (tie).
• pink-tie — the knot tied; takes an l pair, gives an evaluator.
• pink-eval — ((pink-eval src) env) interprets src.
• pink-evalc — the compiling reading; applications of it must be enclosed by the run that scopes their generated code (the Futamura chapter’s discipline).

((pink-eval '(car '(a b))) nil-env)
;=> 'a

Futamura artifacts

Compiled at every boot:

• compiler — pink-eval compiled by pink-evalc (the second projection): an evaluator with the interpretive overhead removed, used exactly like pink-eval.
• evalc-compiled — pink-evalc compiled by itself (the third projection): the compiler as a compiled artifact.

((compiler '(+ 1 2)) nil-env)
;=> 3

Helpers

• nil-env — the empty Pink environment, (lambda _ y 0): every lookup answers 0.
• ((interpret src) env) — pink-eval, spelled as a verb.
• (compile src) — (run 0 ((evalc-compiled src) nil-env)): compile a closed program and execute the residual, all inside one run scope.
• (run-compiled anf) — (run 0 anf) for code compiled within the same scope; code generated loose at the prompt dangles, per the Futamura chapter.

((interpret '(+ 1 2)) nil-env)
;=> 3
(compile '(* 6 7))
;=> 42

The prelude’s five functions (previous chapter) arrive on top of these, and load/define are loop forms, not bindings. Two more names exist in lib/purple.naj but are boot-internal, not installed: load-into, a Pink-path loader that folds a file’s define forms into an environment-as-function, and tower-load, the loader behind the loop’s load.