Updated README

README.md

@@ -6,11 +6,47 @@ Many features are missing, this is still under development.
 
 
 # Features
+ - Open-source
  - Extremely high precision
-   - Uses a rational datatype when possible,
-   - Uses a high-precision float when not.
- - Pretty printing in prompt
-   - Makes expressions shorter and easier to understand
- - Supports nearly all physical units
-   - Accounts for units in calculations
-   - Explicit conversion operator `->` or `to`
+   - Uses a rational datatype when possible, and a high-precision float when not.
+ - Pretty printing in prompt (with special substitutions)
+ - Supports many physical units, with metric and binary prefixes
+ - Supports exponential notation
+ - Clear syntax, parsed input is always re-printed as a sanity check.
+ - Useful, detailed error messages
+
+
+# Usage
+
+All documentation is built into the prompt. Use the `help` command to view it.
+
+## Evaluate expressions:
+ - Basic math: ``103 / 2 * 43``
+ - Functions: ``sqrt(1.4^3 + 4) * sin(pi / 4)``
+ - Scientific notation: ``1.2e12 * 1e-5``
+
+## Physical units
+ - Unit operations: ``2 day + 1 hour``
+ - Unit conversion: ``2 day + 1 hour to minutes``
+ - Compound units: ``10 m/s to mph``
+ - Conversion errors: ``1 liter to volt``
+
+## Varables
+ - Previous answer: `ans + 2`
+ - Variable assignment: `a = 143`
+
+
+# Notes and Tricks
+
+## Unit Conversion
+
+The conversion operator `to` converts its left argument to the *unit* of its right argument, ignoring its value. For example, `5m to mi` and `5m to 10mi` are identical.
+
+
+## Multiplication Order
+
+Implicit multiplication has a higher priority than division. `1/2 pi` will parse as `1/(2pi)`. Type `(1/2) pi` or `1/2 * pi` to get half of pi.
+
+## Inline Assignment
+
+The assignment operator `=` returns its value, and can thus be used inside of an expression. For example, `(a = 2) + 2` assigns `a` to `2` and returns `4`. This only works for variable assignment.