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lex-comment. =
extends $(Lexer)
declare lex
declare rule
level = 0
other: .
lex()
term: $'[*][)]'
if $(not $(eq $(level), 0))
level = $(sub $(level), 1)
lex()
next: $'[(][*]'
level = $(add $(level), 1)
lex()
eof: $"\'"
eprintln(Unterminated comment)
lexer1. =
extends $(Lexer)
declare lex
declare rule
other: .
eprintln(Illegal character: $0)
lex()
white: $'[[:space:]]+'
lex()
comment: $'[(][*]'
lex-comment.lex-channel($(channel))
lex()
op: $'[-+*/()]'
switch $0
case +
Token.unit(plus)
case -
Token.unit(minus)
case *
Token.unit(mul)
case /
Token.unit(div)
case $'('
Token.unit(lparen)
case $')'
Token.unit(rparen)
number: $'[[:digit:]]+'
Token.pair(exp, $(int $0))
eof: $"\'"
Token.unit(eof)
parser1. =
extends $(Parser)
declare rule
#
# Use the main lexer
#
lexer = $(lexer1)
#
# Precedences, in ascending order
#
left(plus minus)
left(mul div)
right(uminus)
#
# A program
#
start(prog)
prog: exp eof
value $1
#
# Simple arithmetic expressions
#
exp: minus exp :prec: uminus
neg($2)
exp: exp plus exp
add($1, $3)
exp: exp minus exp
sub($1, $3)
exp: exp mul exp
mul($1, $3)
exp: exp div exp
div($1, $3)
exp: lparen exp rparen
value $2
println(Test1: should print 48)
println(Parsed $(parser1.parse-file prog, Test.input1))
lexer2. =
extends $(lexer1)
declare rule
lsl: $"<<"
Token.unit(lsl)
lsr: $">>>"
Token.unit(lsr)
asr: $">>"
Token.unit(asr)
parser2. =
extends $(parser1)
declare rule
left(plus, lsl lsr asr)
lexer = $(lexer2)
exp: exp lsl exp
lsl($1, $3)
exp: exp lsr exp
lsr($1, $3)
exp: exp asr exp
asr($1, $3)
println(Test2: should print 256)
println(Parsed $(parser2.parse-file prog, Test.input2))
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