1 files changed, 323 insertions, 55 deletions

diff --git a/src/libzisp/read.zig b/src/libzisp/read.zig
index 9ef9891..812b7c7 100644
--- a/src/libzisp/read.zig
+++ b/src/libzisp/read.zig
@@ -5,101 +5,369 @@ const value = @import("value.zig");
 
 const Value = value.Value;
 
+const Next = enum {
+    start,
+    datum,
+    hash_end,
+    rune_datum_end,
+    quote_end,
+    list,
+    list_end,
+    done,
+};
+
 const State = struct {
     alloc: std.mem.Allocator,
+
     input: []const u8,
     pos: usize = 0,
 
-    next: enum {
-        start,
+    mode: enum { code, data } = .code,
 
-        list,
-        list_end,
+    next: Next = .start,
 
-        err,
+    parent: ?*State = null,
 
-        done,
-    } = .start,
+    last_rune: ?Value = null,
+    list_tail: ?Value = null,
 
     retval: Value = value.eof.eof,
 
-    parent: ?*State = null,
+    fn eof(self: *State) bool {
+        return self.pos >= self.input.len;
+    }
+
+    fn peek(self: *State) u8 {
+        return self.input[self.pos];
+    }
+
+    fn getc(self: *State) u8 {
+        const c = self.peek();
+        self.pos += 1;
+        return c;
+    }
+
+    fn isFinalNull(self: *State) bool {
+        return self.peek() == 0 and self.pos == self.input.len - 1;
+    }
+
+    fn newChild(self: *State, next: Next) *State {
+        const s = self.alloc.create(State) catch @panic("OOM");
+        s.* = State{ .alloc = self.alloc, .input = self.input };
+        s.pos = self.pos;
+        s.mode = self.mode;
+        s.next = next;
+        s.parent = self;
+        return s;
+    }
+
+    fn setReturn(self: *State, val: Value) *State {
+        self.retval = val;
+        self.next = .done;
+        return self;
+    }
+
+    fn finish(self: *State) ?*State {
+        if (self.parent) |p| {
+            p.retval = self.retval;
+            p.pos = self.pos;
+            p.alloc.destroy(self);
+            return p;
+        } else {
+            return null;
+        }
+    }
 };
 
 pub fn read(input: []const u8) Value {
     var gpa: std.heap.GeneralPurposeAllocator(.{}) = .init;
     var top = State{ .alloc = gpa.allocator(), .input = input };
     var s = ⊤
-    while (s.pos <= s.input.len) : (s.pos += 1) {
-        s = switch (s.next) {
-            .start => start(s),
-
-            .list => list(s),
-            .list_end => list(s),
-
-            .err => err(s),
-
-            .done => ret: {
-                if (s.parent) |parent| {
-                    s.alloc.destroy(s);
-                    break :ret parent;
-                } else {
-                    return s.retval;
-                }
-            },
-        };
+    while (true) s = switch (s.next) {
+        .start => start(s),
+        .datum => datum(s),
+        .hash_end => hashEnd(s),
+        .rune_datum_end => runeDatumEnd(s),
+        .quote_end => quoteEnd(s),
+        .list => list(s),
+        .list_end => list(s),
+        .done => s.finish() orelse break,
+    };
+    if (s.eof() or s.isFinalNull()) {
+        return s.retval;
+    } else {
+        @panic("unconsumed input");
     }
-    unreachable;
 }
 
 fn start(s: *State) *State {
-    switch (s.input[s.pos]) {
-        0...8 => s.next = .err,
-
-        '\t', '\n' => {},
+    while (true) {
+        if (s.eof()) {
+            s.next = .done;
+            return s;
+        }
+        const c = s.getc();
+        if (isWhitespace(c)) {
+            continue;
+        }
+        return switch (c) {
+            // whitespace checked above
+            0...31, 127...255 => err(s, "invalid character"),
+            ')', ']', '}' => err(s, "unexpected closing bracket"),
+            ';' => semi(s),
+            else => ret: {
+                // backtrack; let other function handle it
+                s.pos -= 1;
+                break :ret datum(s);
+            },
+        };
+    }
+}
 
-        11...31 => s.next = .err,
+fn semi(s: *State) *State {
+    while (true) {
+        if (s.eof()) {
+            s.next = .done;
+            return s;
+        }
+        const c = s.getc();
+        if (c == '\n') {
+            break;
+        }
+    }
+    return s;
+}
 
-        ' ' => {},
+fn datum(s: *State) *State {
+    const c = s.getc();
+    if (isWhitespace(c)) {
+        return err(s, "expected datum, got whitespace");
+    }
+    return switch (c) {
+        // whitespace checked above
+        0...31, 127...255 => err(s, "invalid character"),
+        ')', ']', '}' => err(s, "unexpected closing bracket"),
+        ';' => err(s, "expected datum, got semicolon"),
+        '"' => string(s),
+        '#' => hash(s),
+        '\'' => quote(s),
+        '(' => list(s),
+        '+' => plus(s),
+        ',' => comma(s),
+        '.' => dot(s),
+        '0'...'9' => number(s),
+        '[' => square(s),
+        '`' => backtick(s),
+        '{' => brace(s),
+        else => symbol(s),
+    };
+}
 
-        '!' => s.next = .err,
+fn isWhitespace(c: u8) bool {
+    return switch (c) {
+        '\t', '\n', ' ' => true,
+        else => false,
+    };
+}
 
-        '"' => quotedString(s),
+// Whitespace, semicolon, and closing brackets of any kind
+fn isEndDelimiter(c: u8) bool {
+    return switch (c) {
+        '\t', '\n', ' ', ';' => true,
+        ')', ']', '}' => true,
+        else => false,
+    };
+}
 
-        else => s.next = .err,
+fn string(s: *State) *State {
+    const str = readString(s) catch return err(s, "unclosed string");
+    if (s.mode == .code) {
+        // "foo bar" => (#string . "foo bar")
+        const rune = value.rune.pack("string");
+        const pair = value.pair.cons(rune, str);
+        return s.setReturn(pair);
+    } else {
+        return s.setReturn(str);
     }
-    return s;
 }
 
-fn quotedString(s: *State) void {
-    var buf: [6]u8 = .{0} ** 6;
-    const len = readString(&buf, s);
-    s.retval = value.pair.cons(
-        value.sstr.pack("quote"),
-        value.pair.cons(
-            value.sstr.pack(buf[0..len]),
-            value.nil.nil,
-        ),
-    );
-    s.next = .done;
+const StringReadError = enum { UnclosedString };
+
+fn readString(s: *State) error{UnclosedString}!Value {
+    return try tryReadSstr(s) orelse readLongString(s);
 }
 
-fn readString(buf: []u8, s: *State) usize {
-    s.pos += 1; // skip opening quote
-    for (s.input[s.pos..], 0..) |c, i| {
+fn tryReadSstr(s: *State) error{UnclosedString}!?Value {
+    // We will reset to this position if we fail.
+    const start_pos = s.pos;
+
+    var buf: [6]u8 = undefined;
+    var i: usize = 0;
+    while (!s.eof()) {
+        const c = s.getc();
         if (c == '"') {
-            s.pos += i;
-            return i;
+            // ok, return what we accumulated
+            return value.sstr.pack(buf[0..i]);
         }
+        if (i == 6) {
+            // failed; reset and bail out
+            s.pos = start_pos;
+            return null;
+        }
+        // ok, save this byte and go on
         buf[i] = c;
+        i += 1;
+    }
+    return error.UnclosedString;
+}
+
+fn readLongString(s: *State) Value {
+    _ = s;
+    @panic("not implemented");
+}
+
+fn hash(s: *State) *State {
+    if (isWhitespace(s.peek())) {
+        return err(s, "whitespace after hash sign");
     }
-    unreachable;
+
+    // is it a datum comment?
+    if (s.peek() == ';') {
+        // consume semicolon
+        _ = s.getc();
+        // Just ignore value and return to starting state after reading it.
+        s.next = .start;
+    } else {
+        s.next = .hash_end;
+    }
+
+    // No whitespace or anything; hash must be immediately followed by datum,
+    // including if it's a datum comment.  Note that if it's actually a rune
+    // we're reading, like #foo, we abuse our ability to reading an sstr here
+    // and later turn it into a rune instead, since they're the same length.
+    return s.newChild(.datum);
+}
+
+fn hashEnd(s: *State) *State {
+    // It's not actually a sstr but a rune, like: #foo or #foo(...)
+    if (value.sstr.check(s.retval)) {
+        return hashRuneEnd(s);
+    }
+
+    // Hash followed by an actual datum; becomes a (#hash ...) invocation:
+    //
+    //   #(...) -> (#hash . (...))
+    //
+    //   #"..." -> (#hash . "...")
+    //
+
+    // But data mode doesn't allow that.
+    if (s.mode == .data) {
+        return err(s, "invalid use of hash in data mode");
+    }
+
+    // Also, bare long strings are not OK here; too similar to a rune.
+    if (value.ptr.checkZisp(s.retval, .string)) {
+        return err(s, "long string after hash sign");
+    }
+
+    return s.setReturn(value.pair.cons(
+        value.rune.pack("hash"),
+        s.retval,
+    ));
+}
+
+// Note: Can only come here from hashEnd().
+fn hashRuneEnd(s: *State) *State {
+    // Convert the fake sstr that was meant to be a rune.
+    const rune = value.rune.make(s.retval);
+
+    // Maybe it's a stand-alone rune, like: #foo
+    if (isEndDelimiter(s.peek())) {
+        // Which is only allowed in data mode.
+        if (s.mode == .code) {
+            return err(s, "bare runes not allowed in code");
+        } else {
+            return s.setReturn(rune);
+        }
+    }
+
+    // Otherwise, it's followed by a datum, like: #foo(...)
+
+    // Which is only allowed in code mode.
+    if (s.mode == .data) {
+        return err(s, "invalid use of hash in data mode");
+    } else {
+        s.last_rune = rune;
+        s.next = .rune_datum_end;
+        return s.newChild(.datum);
+    }
+}
+
+fn runeDatumEnd(s: *State) *State {
+    if (s.last_rune) |rune| {
+        return s.setReturn(value.pair.cons(rune, s.retval));
+    } else {
+        unreachable;
+    }
+}
+
+fn quote(s: *State) *State {
+    // Allowed in Scheme, but why? Not in Zisp.
+    if (isWhitespace(s.peek())) {
+        return err(s, "whitespace after apostrophe");
+    }
+    s.next = .quote_end;
+    const c = s.newChild(.datum);
+    c.mode = .data;
+    return c;
+}
+
+fn quoteEnd(s: *State) *State {
+    return s.setReturn(value.pair.cons(
+        value.rune.pack("quote"),
+        s.retval,
+    ));
 }
 
 fn list(s: *State) *State {
     return s;
 }
 
-fn err(s: *State) *State {
+fn plus(s: *State) *State {
+    return s;
+}
+
+fn comma(s: *State) *State {
+    return s;
+}
+
+fn dot(s: *State) *State {
+    return s;
+}
+
+fn number(s: *State) *State {
+    return s;
+}
+
+fn square(s: *State) *State {
+    return s;
+}
+
+fn backtick(s: *State) *State {
+    return s;
+}
+
+fn brace(s: *State) *State {
+    return s;
+}
+
+fn symbol(s: *State) *State {
     return s;
 }
+
+fn err(s: *State, msg: []const u8) *State {
+    _ = s;
+    std.debug.print("{s}\n", .{msg});
+    @panic("reader error");
+}