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#!/usr/bin/env awk -f
# an evaluator of code
BEGIN {
# prec array contains the precedence order of operators
prec["="] = 1
prec["+"] = prec["-"] = 2
prec["*"] = prec["/"] = 3
prec["^"] = 4
# rigth array contains operators which are right associative
right["="] = right["^"] = 1
split("", code)
split("", mem)
printf "> "
}
{ line = $0; parse(); run(); printf "> " }
function scan() {
sub(/^[ \t]+/, "", line)
if (match(line, /^[0-9]([.0-9]*(e[+-]*)*[0-9])*/)) {
tok = "d" substr(line, 1, RLENGTH)
} else if (match(line, /^([][}{)(,+-=?:]|[*\/รท\^])/)) {
tok = substr(line, 1, RLENGTH)
} else if (match(line, /^[A-Za-z_][A-Za-z_0-9]*/)) {
tok = "v" substr(line, 1, RLENGTH)
} else if (match(line, /^"(\\.|[^\\"])*"/)) {
tok = "s" substr(line, 2, RLENGTH-2)
} else {
tok = "b" substr(line, 1, 1)
}
line = substr(line, RLENGTH+1)
return RLENGTH
}
# TODO: unary operators
function parse( stack, sl, i) {
i = length(code)
while (scan() > 0) {
if (tok == "(") {
stack[++sl] = tok
} else if (tok == ")") {
while (sl && stack[sl] != "(") code[i++] = stack[sl--]
sl--
} else if (tok in prec) {
# Test precedence against stack, or associativity if same precedence
while (sl && (prec[tok] < prec[stack[sl]] || prec[tok] == prec[stack[sl]] && !(stack[sl] in right))) {
code[i++] = stack[sl--]
}
stack[++sl] = tok
} else code[i++] = tok
}
while (sl) code[i++] = stack[sl--]
# for (j = 0; j < i; j++) printf("%s ", code[j]); print ""
}
# TODO: assign, if, while, function
function run( c, i, l, t) {
cl = length(code)
ml = length(mem)
i = 0
while (i < cl) {
c = code[i]
if (c == "+") {
mem[--ml] = mem[ml-1] + mem[ml]
} else if (c == "-") {
mem[--ml] = mem[ml-1] - mem[ml]
} else if (c == "*") {
mem[--ml] = mem[ml-1] * mem[ml]
} else if (c == "/") {
mem[--ml] = mem[ml-1] / mem[ml]
} else if (c == "^") {
mem[--ml] = mem[ml-1] ^ mem[ml]
} else {
mem[++ml] = 0 + substr(c, 2)
}
i++
}
print mem[ml]
# for (i = ml; i in mem; i++) delete mem[i]
}
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