tasks a-s

Task/S-Expressions/D/s-expressions.d

@@ -0,0 +1,90 @@
+import std.stdio: write, writeln;
+import std.conv: text, parse;
+import std.algorithm: canFind;
+import std.variant: Variant;
+import std.uni: isAlpha, isNumber, isWhite;
+
+alias Sexp = Variant;
+
+struct Symbol {
+    private string name;
+    string toString() { return name; }
+}
+
+Sexp parseSexp(in string raw) {
+    static bool isIdentChar(in char c) @safe pure /*nothrow*/ {
+        return c.isAlpha || "0123456789!@#-".canFind(c);
+    }
+
+    size_t pos = 0;
+    while (isWhite(raw[pos])) pos++;
+    Sexp _parse() {
+        size_t i = pos + 1;
+        scope (exit)
+            pos = i;
+        if (raw[pos] == '"') {
+            while (raw[i] != '"' && i < raw.length)
+                i++;
+            i++;
+            return Sexp(raw[pos+1..i-1]);
+        } else if (isNumber(raw[pos])) {
+            while (isNumber(raw[i]) && i < raw.length)
+                i++;
+            if (raw[i] == '.') {
+                i++;
+                while (isNumber(raw[i]) && i < raw.length)
+                    i++;
+                return Sexp(parse!double(raw[pos .. i]));
+            }
+            return Sexp(parse!ulong(raw[pos .. i]));
+        } else if (isIdentChar(raw[pos])) {
+            while (isIdentChar(raw[i]) && i < raw.length)
+                i++;
+            return Sexp(Symbol(raw[pos .. i]));
+        } else if (raw[pos] == '(') {
+            Sexp[] lst;
+            while (raw[i] != ')') {
+                while (isWhite(raw[i]))
+                    i++;
+                pos = i;
+                lst ~= _parse();
+                i = pos;
+                while (isWhite(raw[i]))
+                    i++;
+            }
+            i = pos + 1;
+            return Sexp(lst);
+        }
+        return Sexp(null);
+    }
+    return _parse();
+}
+
+void writeSexp(Sexp expr) {
+    if (expr.type == typeid(string)) {
+        write("\"");
+        write(expr);
+        write("\"");
+    } else if (expr.type == typeid(Sexp[])) {
+        write("(");
+        auto arr = expr.get!(Sexp[]);
+        foreach (immutable i, e; arr) {
+            writeSexp(e);
+            if (i + 1 < arr.length)
+                write(" ");
+        }
+        write(")");
+    } else {
+        write(expr);
+    }
+}
+
+void main() {
+    auto test = `((data "quoted data" 123 4.5)
+     (data (!@# (4.5) "(more" "data)")))`;
+    auto pTest = parseSexp(test);
+    writeln("Parsed: ", pTest);
+    write("Printed: ");
+    writeSexp(pTest);
+    writeln();
+}