diff options
Diffstat (limited to 'src/interp/spad-parser.boot')
| -rw-r--r-- | src/interp/spad-parser.boot | 36 |
1 files changed, 35 insertions, 1 deletions
diff --git a/src/interp/spad-parser.boot b/src/interp/spad-parser.boot index 678c66d2..71f2d60a 100644 --- a/src/interp/spad-parser.boot +++ b/src/interp/spad-parser.boot @@ -42,7 +42,6 @@ -- -- gdr/2007-11-02 -- -import newaux import lexing import parse namespace BOOT @@ -1131,6 +1130,41 @@ for x in ["-", "=", "*", "rem", "mod", "quo", "div", "/", "^", --% +--% +--% Led and Nud have to do with operators. An operator with a Led property +--% takes an operand on its left (infix/suffix operator). +--% +--% An operator with a Nud takes no operand on its left (prefix/nilfix). +--% Some have both (e.g. - ). This terminology is from the Pratt parser. +--% The translator for Scratchpad II is a modification of the Pratt parser +--% which branches to special handlers when it is most convenient and +--% practical to do so (Pratt's scheme cannot handle local contexts very +--% easily). +--% +--% Both LEDs and NUDs have right and left binding powers. This is meaningful +--% for prefix and infix operators. These powers are stored as the values of +--% the LED and NUD properties of an atom, if the atom has such a property. +--% The format is: +--% <Operator Left-Binding-Power Right-Binding-Power <Special-Handler>> +--% where the Special-Handler is the name of a function to be evaluated when +--% that keyword is encountered. +--% +--% The default values of Left and Right Binding-Power are NIL. NIL is a +--% legitimate value signifying no precedence. If the Special-Handler is NIL, +--% this is just an ordinary operator (as opposed to a surfix operator like +--% if-then-else). +--% + +PARSE_-NewKEY := nil + +MAKEOP(x,y,keyname) == + if rest x = nil or integer? second x then + x := [first x,:x] + if alphabetic? stringChar(symbolName first x,0) and + not symbolMember?(first x,symbolValue keyname) then + symbolValue(keyname) := [first x,:symbolValue keyname] + property(first x,y) := x + MAKENEWOP(x,y) == MAKEOP(x,y,'PARSE_-NewKEY) |