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WIP - Lazy pretty printing #65

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WIP - Lazy pretty printing #65

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93 changes: 59 additions & 34 deletions packages/delisp-core/src/prettier.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,17 +11,41 @@

import { InvariantViolation } from "./invariant";

interface Lazy<A> {
type: "lazy";
fn: () => A;
}

function lazy<A>(fn: () => A): Lazy<A> {
let evaluated: A;
return {
type: "lazy",
fn: () => {
if (evaluated) {
return evaluated;
} else {
evaluated = fn();
return evaluated;
}
}
};
}

function force<A>(x: Lazy<A>): A {
return x.fn();
}

interface DocNil {
type: "nil";
}
interface DocText {
type: "text";
content: string;
next: Doc;
next: Lazy<Doc>;
}
interface DocLine {
type: "line";
next: Doc;
next: Lazy<Doc>;
}
interface DocUnion {
type: "union";
Expand All @@ -33,13 +57,13 @@ interface DocAlign {
type: "align";
root: Doc;
docs: Doc[];
next: Doc;
next: Lazy<Doc>;
}
interface DocIndent {
type: "indent";
doc: Doc;
level: number;
next: Doc;
next: Lazy<Doc>;
}
/** A document with potentially multiple layouts. */
export type Doc = DocNil | DocText | DocLine | DocUnion | DocAlign | DocIndent;
Expand All @@ -55,7 +79,7 @@ export function text(content: string): Doc {
if (content.includes("\n")) {
throw new Error(`Newline is not allowed in a call to 'text'`);
}
return { type: "text", content, next: nil };
return { type: "text", content, next: lazy(() => nil) };
}

/** A new line.
Expand All @@ -65,12 +89,12 @@ export function text(content: string): Doc {
*/
export const line: Doc = {
type: "line",
next: nil
next: lazy(() => nil)
};

/** Indent a document by a number of levels. */
export function indent(doc: Doc, level: number): Doc {
return { type: "indent", doc, next: nil, level };
return { type: "indent", doc, next: lazy(() => nil), level };
}

function union(x: Doc, y: Doc, width?: number): Doc {
Expand All @@ -94,7 +118,7 @@ export function align(...docs: Doc[]): Doc {
type: "align",
root,
docs: rest,
next: nil
next: lazy(() => nil)
};
}

Expand All @@ -106,47 +130,47 @@ export function groupalign(x: Doc, y: Doc): Doc {
return union(join([x, y], space), align(x, y));
}

function concat2(x: Doc, y: Doc): Doc {
function concat2Lazy(x: Doc, y: () => Doc): Doc {
switch (x.type) {
case "nil":
return y;
return y();
case "text":
return {
type: "text",
content: x.content,
next: concat2(x.next, y)
next: lazy(() => concat2Lazy(force(x.next), y))
};
case "line":
return {
type: "line",
next: concat2(x.next, y)
next: lazy(() => concat2Lazy(force(x.next), y))
};
case "union":
return {
type: "union",
x: concat2(x.x, y),
y: concat2(x.y, y)
x: concat2Lazy(x.x, y),
y: concat2Lazy(x.y, y)
};
case "align":
return {
type: "align",
root: x.root,
docs: x.docs,
next: concat2(x.next, y)
next: lazy(() => concat2Lazy(force(x.next), y))
};
case "indent":
return {
type: "indent",
doc: x.doc,
next: concat2(x.next, y),
next: lazy(() => concat2Lazy(force(x.next), y)),
level: x.level
};
}
}

/** Concatenate a sequence of documents. */
export function concat(...docs: Doc[]): Doc {
return docs.reduce(concat2, nil);
return docs.reduce((x, y) => concat2Lazy(x, () => y), nil);
}

function flatten(doc: Doc): Doc {
Expand All @@ -157,30 +181,29 @@ function flatten(doc: Doc): Doc {
return {
type: "text",
content: doc.content,
next: flatten(doc.next)
next: lazy(() => flatten(force(doc.next)))
};
case "line":
return {
type: "text",
content: " ",
next: flatten(doc.next)
next: lazy(() => flatten(force(doc.next)))
};
case "union":
// Note that we can just flatten one of the layouts,
// as a union should represent different layouts, they should
// all flatten to the same document.
return flatten(doc.x);
case "align":
return concat(
flatten(join([doc.root, ...doc.docs], space)),
flatten(doc.next)
return concat2Lazy(flatten(join([doc.root, ...doc.docs], space)), () =>
flatten(force(doc.next))
);
case "indent":
return {
type: "indent",
level: doc.level,
doc: flatten(doc.doc),
next: flatten(doc.next)
next: lazy(() => flatten(force(doc.next)))
};
}
}
Expand All @@ -201,7 +224,7 @@ export function group(doc: Doc, width?: number): Doc {
return {
type: "text",
content: doc.content,
next: group(doc.next, width)
next: lazy(() => group(force(doc.next), width))
};
case "line":
return union(flatten(doc), doc, width);
Expand All @@ -222,7 +245,7 @@ export function group(doc: Doc, width?: number): Doc {
type: "indent",
level: doc.level,
doc: group(doc.doc, width),
next: group(doc.next, width)
next: lazy(() => group(force(doc.next), width))
};
}
}
Expand Down Expand Up @@ -258,7 +281,7 @@ function fits(doc: Doc, w: number): boolean {
case "line":
return true;
case "text":
return fits(doc.next, w - doc.content.length);
return fits(force(doc.next), w - doc.content.length);
case "union":
throw new InvariantViolation(
`unions should be removed before checking if it fits.`
Expand All @@ -282,12 +305,12 @@ function best(doc: Doc, w: number, k: number): Doc {
return {
type: "text",
content: doc.content,
next: best(doc.next, w, k + doc.content.length)
next: lazy(() => best(force(doc.next), w, k + doc.content.length))
};
case "line":
return {
type: "line",
next: best(doc.next, w, 0)
next: lazy(() => best(force(doc.next), w, 0))
};
case "union":
if (doc.width) {
Expand All @@ -306,14 +329,14 @@ function best(doc: Doc, w: number, k: number): Doc {
type: "align",
root: best(doc.root, w, k),
docs: doc.docs.map(d => best(d, w, k)),
next: best(doc.next, w, k)
next: lazy(() => best(force(doc.next), w, k))
};
case "indent":
return {
type: "indent",
doc: best(doc.doc, w - doc.level, k),
level: doc.level,
next: best(doc.next, w, k)
next: lazy(() => best(force(doc.next), w, k))
};
}
}
Expand All @@ -331,11 +354,13 @@ function layout(doc: Doc, indentation: number, alignment: number): string {
case "text":
return (
doc.content +
layout(doc.next, indentation, alignment + doc.content.length)
layout(force(doc.next), indentation, alignment + doc.content.length)
);
case "line":
return (
"\n" + repeatChar(" ", indentation) + layout(doc.next, indentation, 0)
"\n" +
repeatChar(" ", indentation) +
layout(force(doc.next), indentation, 0)
);
case "union":
throw new InvariantViolation(`No layout for unions!`);
Expand All @@ -348,12 +373,12 @@ function layout(doc: Doc, indentation: number, alignment: number): string {
repeatChar(" ", indentation + alignment) +
layout(d, indentation + alignment, 0)
)
].join("\n") + layout(doc.next, indentation, alignment)
].join("\n") + layout(force(doc.next), indentation, alignment)
);
case "indent":
return (
layout(doc.doc, indentation + doc.level, alignment) +
layout(doc.next, indentation, alignment)
layout(force(doc.next), indentation, alignment)
);
}
}
Expand Down