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const std = @import("std");
pub const Token = struct {
loc: Location,
type: Type,
pub const Type = union(enum) {
left_paren,
right_paren,
integer_literal,
plus,
minus,
invalid,
eof,
};
};
pub const Location = struct {
start: usize,
end: usize,
pub fn combine(a: Location, b: Location) Location {
if (a.end > b.start) unreachable;
return .{ .start = @min(a.start, b.start), .end = @max(a.end, b.end) };
}
/// Assumes that the location comes directly from an `integer_literal` token.
pub fn getInt(self: Location, file_source: []const u8) u64 {
var value: u64 = 0;
for (file_source[self.start..self.end]) |c| {
std.debug.assert('0' <= c and c <= '9');
value = value * 10 + (c - '0');
}
return value;
}
};
source: []const u8,
last_end: usize = 0,
pos: usize = 0,
pub fn next(self: *Self) ?Token {
return s: switch (self.eat() orelse return self.create(.eof)) {
'(' => self.create(.left_paren),
')' => self.create(.right_paren),
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => self.integerLiteral(),
'+' => self.create(.plus),
'-' => self.create(.minus),
' ' => {
self.last_end = self.pos;
continue :s (self.eat() orelse return self.create(.eof));
},
else => self.create(.invalid),
};
}
fn integerLiteral(self: *Self) Token {
var value: ?u64 = 0;
while (digitValue(self.peek())) |v| {
var nxt: ?u64 = null;
if (value) |val|
if (std.math.mul(u64, val, 10) catch null) |p|
if (std.math.add(u64, p, v) catch null) |s| {
nxt = s;
};
value = nxt;
_ = self.eat();
}
return if (value != null)
self.create(.{ .integer_literal = {} })
else
self.create(.{ .invalid = {} });
}
fn create(self: *Self, tajp: Token.Type) Token {
const start = self.last_end;
self.last_end = self.pos;
return .{ .loc = .{ .start = start, .end = self.pos }, .type = tajp };
}
fn eat(self: *Self) ?u8 {
const token = self.peek();
if (token != null) self.pos += 1;
return token;
}
fn peek(self: *Self) ?u8 {
return if (self.pos < self.source.len) self.source[self.pos] else null;
}
const Self = @This();
fn digitValue(c: ?u8) ?u8 {
return switch (c orelse return null) {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9' => c.? - '0',
else => null,
};
}
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