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global defs, ifile, in, limit, tswitch, prompt
record nonterm(name)
record charset(chars)
record query(name)
procedure main(x)
local line, plist
plist := [define,generate,grammar,source,comment,prompter,error]
defs := table()
defs["lb"] := [["<"]]
defs["rb"] := [[">"]]
defs["vb"] := [["|"]]
defs["nl"] := [["\n"]]
defs[""] := [[""]]
defs["&lcase"] := [[charset(&lcase)]]
defs["&ucase"] := [[charset(&ucase)]]
defs["&digit"] := [[charset('0123456789')]]
i := 0
while i < *x do {
s := x[i +:= 1] | break
case s of {
"-t": tswitch := 1
"-l": limit := integer(x[i +:= 1]) | stop("usage: [-t] [-l n]")
default: stop("usage: [-t] [-l n]")
}
}
ifile := [&input]
prompt := ""
test := ["<a>::=1|2|3","<a>10","->","<b>::=<a>|<a><a>|<b><b>","<b>5",
"<c>::=<b><b><b>","<c>100","<b>100"]
every line := !test do {
(!plist)(line)
collect()
every write(&collections)
write("----------")
}
end
procedure comment(line)
if line[1] == "#" then return
end
procedure define(line)
return line ?
defs[(="<",tab(find(">::=")))] := (move(4),alts(tab(0)))
end
procedure defnon(sym)
if sym ? {
="'" &
chars := cset(tab(-1)) &
="'"
}
then return charset(chars)
else if sym ? {
="?" &
name := tab(0)
}
then return query(name)
else return nonterm(sym)
end
procedure error(line)
write("*** erroneous line: ",line)
return
end
procedure gener(goal)
local pending, genstr, symbol
repeat {
pending := [nonterm(goal)]
genstr := ""
while symbol := get(pending) do {
if \tswitch then write(genstr,symimage(symbol),listimage(pending))
case type(symbol) of {
"string": genstr ||:= symbol
"charset": genstr ||:= ?symbol.chars
"query": {
writes("*** supply string for ",symbol.name," ")
genstr ||:= read() | {
write("*** no value for query to ",symbol.name)
suspend genstr
break next
}
}
"nonterm": {
pending := ?\defs[symbol.name] ||| pending | {
write("*** undefined nonterminal: <",symbol.name,">")
suspend genstr
break next
}
if *pending > \limit then {
write("*** excessive symbols remaining")
suspend genstr
break next
}
}
}
}
suspend genstr
}
end
procedure generate(line)
local goal, count
if line ? {
="<" &
goal := tab(upto('>')) \ 1 &
move(1) &
count := (pos(0) & 1) | integer(tab(0))
}
then {
every write(gener(goal)) \ count
return
}
else fail
end
procedure getrhs(a)
local rhs
rhs := ""
every rhs ||:= sform(!a) || "|"
return rhs[1:-1]
end
procedure grammar(line)
local file, out
if line ? {
name := tab(find("->")) &
move(2) &
file := tab(0) &
out := if *file = 0 then &output else {
open(file,"w") | {
write("*** cannot open ",file)
fail
}
}
}
then {
(*name = 0) | (name[1] == "<" & name[-1] == ">") | fail
pwrite(name,out)
if *file ~= 0 then close(out)
return
}
else fail
end
procedure listimage(a)
local s, x
s := ""
every x := !a do
s ||:= symimage(x)
return s
end
procedure alts(defn)
local alist
alist := []
defn ? while put(alist,syms(tab(many(~'|')))) do move(1)
return alist
end
procedure prompter(line)
if line[1] == "=" then {
prompt := line[2:0]
return
}
end
procedure pwrite(name,ofile)
local nt, a
static builtin
initial builtin := ["lb","rb","vb","nl","","&lcase","&ucase","&digit"]
if *name = 0 then {
a := sort(defs)
every nt := !a do {
if nt[1] == !builtin then next
write(ofile,"<",nt[1],">::=",getrhs(nt[2]))
}
}
else write(ofile,name,"::=",getrhs(\defs[name[2:-1]])) |
write("*** undefined nonterminal: ",name)
end
procedure sform(alt)
local s, x
s := ""
every x := !alt do
s ||:= case type(x) of {
"string": x
"nonterm": "<" || x.name || ">"
"charset": "<'" || x.chars || "'>"
}
return s
end
procedure source(line)
return line ? (="@" & push(ifile,in) & {
in := open(file := tab(0)) | {
write("*** cannot open ",file)
fail
}
})
end
procedure symimage(x)
return case type(x) of {
"string": x
"nonterm": "<" || x.name || ">"
"charset": "<'" || x.chars || "'>"
}
end
procedure syms(alt)
local slist
slist := []
alt ? while put(slist,tab(many(~'<')) |
defnon(2(="<",tab(upto('>')),move(1))))
return slist
end
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