Layout failure.

Empty document.

Literal content with display width.

Hard line break. Cannot be flattened.

Line break, or space when flattened.

Line break, or empty when flattened.

flatAlt default flat: use default normally, flat when flattened by group.

Increase nesting by i.

Layout alternatives. Invariant: first argument is the flattened form of the second.

Attach an annotation.

React to the current column position.

React to the current nesting level.

Replace FlatAlt with its flat branch, Line with Fail.

Implemented as a fold — children are flattened first, so Column/Nesting functions automatically produce flattened subtrees.

Try to lay out the document on a single line. Falls back to the original if flattening fails.

group x = union (flatten x) x

Lay out relative to the current column rather than the current nesting level.

align d = column (\k -> nesting (\i -> nest (k - i) d))

A line break that behaves like a space when flattened by group.

softline = group line

A line break that vanishes when flattened by group.

softline' = group line'

Concatenate with a space in between.

Concatenate documents using a binary operator.

Concatenate with spaces.

Concatenate with line separators.

Concatenate with softline separators.

vsep that tries to fit on one line (group).

Concatenate without separators.

Concatenate with line' separators (line or empty).

Concatenate with softline' separators.

vcat that tries to fit on one line (group).

hang i doc = align (nest i doc)

indent i doc inserts i spaces then aligns.

surround mid left right = left <> mid <> right

Enclose a list with separators.

encloseSep lbrace rbrace comma [a, b, c] = lbrace <> a <> comma <> b <> comma <> c <> rbrace

When the content fits, renders on one line. Otherwise, each element gets its own line, aligned.

list = encloseSep "[" "]" ", "

tupled = encloseSep "(" ")" ", "

Append a separator to all but the last element.

width doc f renders doc then passes its rendered width to f.

fill n doc pads doc to width n with spaces.

fillBreak n doc pads or breaks after doc if it exceeds n.

Map over annotations.

Remove all annotations.

Alter annotations, potentially adding or removing layers.

Result of checking whether flattening changes a document.

Check whether flattening changes a document, and if so, produce the flattened version.

This is the key optimization for group': by checking first, we avoid creating unnecessary Union nodes.

Uses direct recursion via unwrap (matching prettyprinter's approach). A zygomorphism formulation is possible but less readable.

Optimized group: avoids creating Union when the document is already flat or can never be flattened.

pretty opts (group' doc) = pretty opts (group doc)

Merge adjacent Leaf nodes and collapse nested Nest.

This is a semantic no-op — the rendered output is identical — but reduces tree size for more efficient layout.

Operates as a fold (catamorphism). Does not recurse into Column/Nesting functions.

pretty opts (fuse doc) = pretty opts doc

Remove trailing whitespace from rendered output.

Drops spaces at the end of each line. Applied as a post-processing step on the rendered string.

A single rendered token. The output of the layout algorithm.

Page width configuration.

Layout options.

80 columns, ribbon fraction 1.0.

Wadler/Leijen layout with one-line lookahead.

At Union nodes, tries the flattened (first) branch. If the remainder of the line fits within the page width, uses it. Otherwise falls back to the second (default) branch.

Smart layout with multi-line lookahead.

Like layoutPretty, but the fitting predicate checks beyond the first line break — it continues checking until it finds a line that starts at the same or shallower indentation level. This prevents surprises where content looks like it fits but subsequent lines overflow.

Use this for deeply nested structures where layoutPretty makes suboptimal choices.

Compact layout: no width-sensitivity, always breaks.

Every FlatAlt uses its default, every Union uses the narrow branch. Column and Nesting receive 0.

Wadler/Leijen layout producing a Nu stream.

Unlike layoutPretty which materializes a [Token] list, layoutStream produces a Nu (Cons (Token m ann)) — a seed + step function that generates tokens lazily on demand. Construction is O(1); tokens are computed as they are consumed.

Render a Nu token stream to the output monoid.

Streaming layout + render.

prettyStream opts = renderStream . layoutStream opts

Render a token stream to the output monoid, discarding annotations.

Lay out and render a document.

pretty opts = render . layoutPretty opts