Added a UnitParser to get Dimensions and Scales from a str

src/Scales.zig

@@ -59,7 +59,8 @@ pub const UnitScale = enum(isize) {
         var buf: [16]u8 = undefined;
         return switch (self) {
             .none => "",
-            .P, .T, .G, .M, .k, .h, .da, .d, .c, .m, .u, .n, .p, .f, .min, .hour, .year, .inch, .ft, .yd, .mi, .oz, .lb, .st => @tagName(self),
+            .P, .T, .G, .M, .k, .h, .da, .d, .c, .m, .u, .n, .p, .f, .min, .year, .inch, .ft, .yd, .mi, .oz, .lb, .st => @tagName(self),
+            .hour => "h",
             else => std.fmt.bufPrint(&buf, "[{d}]", .{@intFromEnum(self)}) catch "[]", // This cannot be inline because of non exhaustive enum, but that's ok, it is just str, not calculation
         };
     }

src/UnitParser.zig

@@ -0,0 +1,145 @@
+const std = @import("std");
+const Dimensions = @import("Dimensions.zig");
+const Scales = @import("Scales.zig");
+
+/// A container returning the separated arguments needed to construct a Tensor.
+pub const ParsedUnit = struct {
+    dims: Dimensions.ArgOpts = .{},
+    scales: Scales.ArgOpts = .{},
+};
+
+pub const UnitParseError = error{
+    UnknownBaseUnit,
+    UnknownPrefix,
+    InvalidExponent,
+    EmptyStr,
+};
+
+/// Parses strings like "km/s^2", "m", "kg*m/s^2", "1/min".
+/// Evaluates entirely at comptime.
+pub fn parseUnit(comptime str: []const u8) !ParsedUnit {
+    if (str.len == 0) return UnitParseError.EmptyStr;
+
+    var parsed: ParsedUnit = .{ .dims = .{}, .scales = .{} };
+
+    // We need to track if we are after a '/' to flip exponents to negative
+    var is_denominator = false;
+
+    // Manual iteration to handle '/' properly
+    var cursor: usize = 0;
+    while (cursor < str.len) {
+        // Find the next segment
+        const segment_start = cursor;
+        while (cursor < str.len and str[cursor] != '/' and str[cursor] != '.' and str[cursor] != '*') : (cursor += 1) {}
+        const segment = str[segment_start..cursor];
+
+        if (segment.len > 0) {
+            try parseSegment(segment, &parsed, is_denominator);
+        }
+
+        if (cursor < str.len) {
+            if (str[cursor] == '/') {
+                is_denominator = true;
+            }
+            cursor += 1; // skip the separator
+        }
+    }
+
+    return parsed;
+}
+
+fn parseSegment(comptime segment: []const u8, parsed: *ParsedUnit, is_denominator: bool) !void {
+    var scale: Scales.UnitScale = .none;
+    var found_scale = false;
+    var active_dim: ?Dimensions.Dimension = null;
+
+    // 1. Try to find a Scale + Dimension pair (e.g., "mm", "km")
+    inline for (std.enums.values(Scales.UnitScale)) |sca| {
+        const s_str = sca.str();
+        if (s_str.len > 0 and std.mem.startsWith(u8, segment, s_str)) {
+            // Check if it's a "Unit-as-Scale" (hour, min) or a prefix (k, m, c)
+            switch (sca) {
+                .hour, .min, .year => {
+                    // These are dimensions themselves (Time)
+                    if (segment.len == s_str.len or (segment.len > s_str.len and (segment[s_str.len] == '^' or (segment[s_str.len] >= '0' and segment[s_str.len] <= '9')))) {
+                        scale = sca;
+                        active_dim = .T;
+                        found_scale = true;
+                    }
+                },
+                else => {
+                    // Standard prefixes: Must be followed by a valid dimension unit
+                    inline for (std.enums.values(Dimensions.Dimension)) |dim| {
+                        if (std.mem.startsWith(u8, segment[s_str.len..], dim.unit())) {
+                            scale = sca;
+                            active_dim = dim;
+                            found_scale = true;
+                            break;
+                        }
+                    }
+                },
+            }
+        }
+        if (found_scale) break;
+    }
+
+    // 2. If no scale prefix was found, try identifying as a pure Dimension (e.g., "m", "s")
+    if (!found_scale) {
+        inline for (std.enums.values(Dimensions.Dimension)) |dim| {
+            if (std.mem.startsWith(u8, segment, dim.unit())) {
+                active_dim = dim;
+                break;
+            }
+        }
+    }
+
+    const dimen = active_dim orelse return UnitParseError.UnknownBaseUnit;
+
+    // 3. Determine where the exponent starts
+    // If it was a Time Scale (like 'h'), the exponent starts after 'h'
+    // If it was a Prefix + Dim (like 'km'), it starts after 'km'
+    const unit_part_len = if (found_scale)
+        (if (scale == .hour or scale == .min or scale == .year) scale.str().len else scale.str().len + dimen.unit().len)
+    else
+        dimen.unit().len;
+
+    const expo_str = segment[unit_part_len..];
+
+    // 4. Parse Exponent
+    var expo: i32 = 1;
+    if (expo_str.len > 0) {
+        const cleaned_expo = if (expo_str[0] == '^') expo_str[1..] else expo_str;
+        expo = std.fmt.parseInt(i32, cleaned_expo, 10) catch return UnitParseError.InvalidExponent;
+    }
+
+    if (is_denominator) expo *= -1;
+
+    // 5. Assign to struct
+    inline for (std.meta.fields(Dimensions.ArgOpts)) |f| {
+        if (std.mem.eql(u8, f.name, @tagName(dimen))) {
+            @field(parsed.dims, f.name) += expo;
+            @field(parsed.scales, f.name) = scale;
+        }
+    }
+}
+
+inline fn testParser(
+    comptime str: []const u8,
+    comptime expected_dims: Dimensions.ArgOpts,
+    comptime expected_scales: Scales.ArgOpts,
+) !void {
+    const unit = comptime try parseUnit(str);
+    if (comptime !Dimensions.init(expected_dims).eql(Dimensions.init(unit.dims))) return error.WrongDims;
+    if (comptime !Scales.init(expected_scales).eql(Scales.init(unit.scales))) return error.WrongScales;
+}
+
+test "parseUnit" {
+    @setEvalBranchQuota(10000);
+    try testParser("m", .{ .L = 1 }, .{});
+    try testParser("s", .{ .T = 1 }, .{});
+    try testParser("mm", .{ .L = 1 }, .{ .L = .m });
+    try testParser("m/s", .{ .L = 1, .T = -1 }, .{});
+    try testParser("m1/s2/kg", .{ .L = 1, .T = -2, .M = -1 }, .{ .M = .k });
+    try testParser("km/h", .{ .L = 1, .T = -1 }, .{ .L = .k, .T = .hour });
+    try testParser("m.s^-1", .{ .L = 1, .T = -1 }, .{});
+}

src/main.zig

@@ -4,10 +4,12 @@ pub const Tensor = @import("Tensor.zig").Tensor;
 pub const Dimensions = @import("Dimensions.zig");
 pub const Scales = @import("Scales.zig");
 pub const Base = @import("Base.zig");
+pub const UnitParser = @import("UnitParser.zig");
 
 test {
     _ = @import("Tensor.zig");
     _ = @import("Dimensions.zig");
     _ = @import("Scales.zig");
     _ = @import("Base.zig");
+    _ = @import("UnitParser.zig");
 }