hera-py 0.4.0

Interpreter for the Haverford Educational RISC Architecture (HERA) assembly language

hera-py

An interpreter for the Haverford Educational RISC Architecture (HERA) assembly language.

Installation

You can install hera-py with pip:

$ pip3 install hera-py

Usage

After installation, hera-py can be invoked with the hera command to run a HERA program:

$ hera my-hera-file.hera

You can also preprocess a HERA program without running it, to see how pseudo-instructions and labels are resolved to HERA code:

$ hera preprocess my-hera-file.hera

Comparison with HERA-C

HERA-C is the current HERA interpreter used as Haverford. It is implemented as a shell-script wrapper around a set of C++ macros that expand HERA instructions into C++ code. hera-py aims to improve on HERA-C in the following areas:

• Ease of use
  • Cross-platform and easy to install
  • Configurable with command-line options
  • Does not create temporary files
  • Can read programs from stdin
  • Command name has six fewer letters than HERA-C-Run
• Helpful error messages
• Simple debugging

hera-py also supports several features that HERA-C does not:

• Multi-precision multiplication
• Relative branching by a fixed integer value (e.g., BRR(10))
• Branching by the value of a register (e.g., SET(R1, 20); BR(R1))
• Setting registers to the value of a label

HERA-C has a few features that hera-py does not:

• C-style #define macros (and more generally the ability to embed arbitrary C++ code in HERA programs)
• Relative branching to labels (though the same outcome can be achieved with register-mode branching)

Design

Running a HERA program takes a few steps:

1. The text of the program is parsed into a list of instruction objects. (hera/parser.py)
2. The symbol table for the program is generated. (hera/symtab.py)
3. The program is type-checked to ensure that all operations take the proper number and type of operands. (hera/typechecker.py)
4. Pseudo-instructions are converted into actual instructions, and labels and constants are substituted for their values. (hera/preprocessor.py)
5. The instructions are executed on a virtual HERA machine. (hera/vm.py)

For more details about the implementation, see the docstrings in each module.