author | paulson |
Fri, 01 Nov 1996 15:39:37 +0100 | |
changeset 2149 | 639db8177804 |
parent 1508 | 20d9811f1fd1 |
child 2695 | 871b69a4b78f |
permissions | -rw-r--r-- |
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(* Title: Pure/Syntax/pretty.ML |
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ID: $Id$ |
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Author: Lawrence C Paulson |
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Copyright 1991 University of Cambridge |
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Generic pretty printing module. |
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Loosely based on |
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D. C. Oppen, "Pretty Printing", |
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ACM Transactions on Programming Languages and Systems (1980), 465-483. |
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The object to be printed is given as a tree with indentation and line |
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breaking information. A "break" inserts a newline if the text until |
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the next break is too long to fit on the current line. After the newline, |
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text is indented to the level of the enclosing block. Normally, if a block |
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is broken then all enclosing blocks will also be broken. Only "inconsistent |
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breaks" are provided. |
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The stored length of a block is used in breakdist (to treat each inner block as |
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a unit for breaking). |
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*) |
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type pprint_args = (string -> unit) * (int -> unit) * (int -> unit) * |
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(unit -> unit) * (unit -> unit); |
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signature PRETTY = |
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sig |
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type T |
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val blk: int * T list -> T |
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val brk: int -> T |
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val fbrk: T |
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val str: string -> T |
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val lst: string * string -> T list -> T |
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val quote: T -> T |
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val commas: T list -> T list |
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val breaks: T list -> T list |
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val fbreaks: T list -> T list |
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val block: T list -> T |
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val strs: string list -> T |
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val enclose: string -> string -> T list -> T |
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val list: string -> string -> T list -> T |
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val str_list: string -> string -> string list -> T |
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val big_list: string -> T list -> T |
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val string_of: T -> string |
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val writeln: T -> unit |
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val str_of: T -> string |
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val pprint: T -> pprint_args -> unit |
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val map_strs: (string -> string) -> T -> T |
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val setdepth: int -> unit |
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val setmargin: int -> unit |
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end; |
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structure Pretty : PRETTY = |
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struct |
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(*Printing items: compound phrases, strings, and breaks*) |
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datatype T = Block of T list * int * int (*indentation, length*) |
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| String of string |
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| Break of bool*int (*mandatory flag; width if not taken*); |
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(*Add the lengths of the expressions until the next Break; if no Break then |
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include "after", to account for text following this block. *) |
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fun breakdist (Block(_,_,len)::es, after) = len + breakdist(es, after) |
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| breakdist (String s :: es, after) = size s + breakdist (es, after) |
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| breakdist (Break _ :: es, after) = 0 |
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| breakdist ([], after) = after; |
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fun repstring a 0 = "" |
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| repstring a 1 = a |
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| repstring a k = |
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if k mod 2 = 0 then repstring(a^a) (k div 2) |
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else repstring(a^a) (k div 2) ^ a; |
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(*** Type for lines of text: string, # of lines, position on line ***) |
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type text = {tx: string, nl: int, pos: int}; |
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val emptytext = {tx="", nl=0, pos=0}; |
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fun blanks wd {tx,nl,pos} = |
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{tx = tx ^ repstring " " wd, |
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nl = nl, |
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pos = pos+wd}; |
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fun newline {tx,nl,pos} = |
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{tx = tx ^ "\n", |
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nl = nl+1, |
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pos = 0}; |
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fun string s {tx,nl,pos} = |
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{tx = tx ^ s, |
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nl = nl, |
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pos = pos + size(s)}; |
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(*** Formatting ***) |
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val margin = ref 80 (*right margin, or page width*) |
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and breakgain = ref 4 (*minimum added space required of a break*) |
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and emergencypos = ref 40; (*position too far to right*) |
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fun setmargin m = |
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(margin := m; |
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breakgain := !margin div 20; |
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emergencypos := !margin div 2); |
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(*Search for the next break (at this or higher levels) and force it to occur*) |
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fun forcenext [] = [] |
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| forcenext (Break(_,wd) :: es) = Break(true,0) :: es |
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| forcenext (e :: es) = e :: forcenext es; |
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(*es is list of expressions to print; |
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blockin is the indentation of the current block; |
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after is the width of the following context until next break. *) |
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fun format ([], _, _) text = text |
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| format (e::es, blockin, after) (text as {pos,nl,...}) = |
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(case e of |
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Block(bes,indent,wd) => |
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let val blockin' = (pos + indent) mod !emergencypos |
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val btext = format(bes, blockin', breakdist(es,after)) text |
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(*If this block was broken then force the next break.*) |
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val es2 = if nl < #nl(btext) then forcenext es else es |
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in format (es2,blockin,after) btext end |
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| String s => format (es,blockin,after) (string s text) |
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| Break(force,wd) => (*no break if text to next break fits on this line |
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or if breaking would add only breakgain to space *) |
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format (es,blockin,after) |
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(if not force andalso |
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pos+wd <= Int.max(!margin - breakdist(es,after), |
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blockin + !breakgain) |
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then blanks wd text (*just insert wd blanks*) |
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else blanks blockin (newline text))); |
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(*** Exported functions to create formatting expressions ***) |
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fun length (Block(_,_,len)) = len |
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| length (String s) = size s |
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| length (Break(_,wd)) = wd; |
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val str = String |
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and fbrk = Break(true,0); |
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fun brk wd = Break(false,wd); |
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fun blk (indent,es) = |
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let fun sum([], k) = k |
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| sum(e::es, k) = sum(es, length e + k) |
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in Block(es,indent, sum(es,0)) end; |
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(*Join the elements of es as a comma-separated list, bracketted by lp and rp*) |
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fun lst(lp,rp) es = |
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let fun add(e,es) = str"," :: brk 1 :: e :: es; |
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fun list(e :: (es as _::_)) = str lp :: e :: foldr add (es,[str rp]) |
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| list(e::[]) = [str lp, e, str rp] |
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| list([]) = [] |
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in blk(size lp, list es) end; |
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(* utils *) |
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fun quote prt = |
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blk (1, [str "\"", prt, str "\""]); |
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fun commas prts = |
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flat (separate [str ",", brk 1] (map (fn x => [x]) prts)); |
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fun breaks prts = separate (brk 1) prts; |
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fun fbreaks prts = separate fbrk prts; |
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fun block prts = blk (2, prts); |
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val strs = block o breaks o (map str); |
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fun enclose lpar rpar prts = |
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block (str lpar :: (prts @ [str rpar])); |
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fun list lpar rpar prts = |
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enclose lpar rpar (commas prts); |
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fun str_list lpar rpar strs = |
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list lpar rpar (map str strs); |
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fun big_list name prts = |
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block (fbreaks (str name :: prts)); |
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(*** Pretty printing with depth limitation ***) |
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val depth = ref 0; (*maximum depth; 0 means no limit*) |
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fun setdepth dp = (depth := dp); |
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(*Recursively prune blocks, discarding all text exceeding depth dp*) |
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fun pruning dp (Block(bes,indent,wd)) = |
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if dp>0 then blk(indent, map (pruning(dp-1)) bes) |
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else String"..." |
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| pruning dp e = e; |
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fun prune dp e = if dp>0 then pruning dp e else e; |
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fun string_of e = #tx (format ([prune (!depth) e], 0, 0) emptytext); |
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val writeln = writeln o string_of; |
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(*Create a single flat string: no line breaking*) |
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fun str_of prt = |
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let |
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fun s_of (Block (prts, _, _)) = implode (map s_of prts) |
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| s_of (String s) = s |
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| s_of (Break (false, wd)) = repstring " " wd |
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| s_of (Break (true, _)) = " "; |
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in |
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s_of (prune (! depth) prt) |
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end; |
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(*Part of the interface to the Poly/ML and New Jersey ML pretty printers*) |
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fun pprint prt (put_str, begin_blk, put_brk, put_fbrk, end_blk) = |
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let |
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fun pp (Block (prts, ind, _)) = (begin_blk ind; pp_lst prts; end_blk ()) |
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| pp (String s) = put_str s |
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| pp (Break (false, wd)) = put_brk wd |
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| pp (Break (true, _)) = put_fbrk () |
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and pp_lst [] = () |
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| pp_lst (prt :: prts) = (pp prt; pp_lst prts); |
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in |
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pp (prune (! depth) prt) |
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end; |
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(*Map strings*) |
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fun map_strs f (Block (prts, ind, _)) = blk (ind, map (map_strs f) prts) |
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| map_strs f (String s) = String (f s) |
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| map_strs _ brk = brk; |
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(*** Initialization ***) |
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val () = setmargin 80; |
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end; |
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