ev: implement parse and run

1 files changed, 77 insertions, 1 deletions

diff --git a/ev b/ev
index b5f178c..fede0e3 100644..100755
--- a/ev
+++ b/ev
@@ -3,7 +3,83 @@
 # 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)
+	# print "# line: '"  line "'"
+	if (match(line, /^[.0-9]+/)) {
+		tok = "d" substr(line, 1, RLENGTH)
+	} else if (match(line, /^([][}{)(,+-=?:]|[*\/÷\^])/)) {
+		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)
+	}
+	# cnum += RLENGTH
+	line = substr(line, RLENGTH+1)
+	# print "# scan: RLENGTH=" RLENGTH
+	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 ""
 }
 
-eval(mem, src) {
+# TODO: assign
+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]
 }