CSE-112 • Fall 2020 • Program 2 • Interpreter in Ocaml 1 of 3
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1. Overview
This project will repeat the Mini Basic interpreter, except this time the program will
be written in Ocaml but with Mini Basic programs untranslated from the original.
See the .score/ directory for sample input files. Output should be the same as for
the Scheme version of the program, except for minor variations in output due to dif-
ferences between the Scheme and Ocaml languages. Any results which would pro-
duce a complex value in Scheme should produce nan in this project.
2. Running ocaml interactively
Ocaml may be run interactively from the command line or as a compiled program.
The compiled program version, created using make is required for all submitted pro-
grams.
To run ocaml interactively, add the following to your $HOME/.bash_profile :
export PATH=$PATH:/afs/cats.ucsc.edu/courses/cse112-wm/usr/ocaml/bin
When running ocaml interactively, use the command rlwrap to gain access to the
readline arrow keys so that you can recover earlier typed lines. Example :
-bash-$ rlwrap ocaml
OCaml version 4.02.1
# let f x y = x +. y;;
val f : float -> float -> float =
# f 3.;;
- : float -> float =
# f 3. 4.;;
- : float = 7.
# ^D
To simplify typing, the following line might be added to your $HOME/.bash_profile :
alias wocaml="rlwrap ocaml"
The suggestions above assume you are using bash as your login shell. If not, use the
syntax appropriate for whatever shell you are using.
Some files that are useful when running interactively are :
using
A set of #use directives which can be used for interactive testing of the func-
tions. This file is not used in compilation. After starting Ocaml, type in the
following command to load your source code interactively :
#use "using";;
.ocamlinit
As an alternative to the using file, create the file .ocamlinit containing the
same information. The file .ocamlinit in the current directory is automati-
cally sourced when ocaml starts.
As an alternative, start up ocaml with the line
rlwrap ocaml -init using
which will start up the init file when needed, but avoid the automatic startup when
you don’t want it. If you have a .ocamlinit and want to ocassionally suppress it,
CSE-112 • Fall 2020 • Program 2 • Interpreter in Ocaml 2 of 3
you can use
rlwrap ocaml -init /dev/null
3. Source code
The following files and modules are provided in the code/ subdirectory :
etc.mli, etc.ml
Interface and implementation of the Etc module, which contains miscellaneous
functions not specifically tied to other purposes.
absyn.mli
Definition of the abstract syntax used by the interpreter. No implementation
file is needed.
tables.mli, tables.ml
Module for maintaining the five tables needed by the program. The interface
file is automatically generated from the implemenation, not entered manually.
The required tables and their types are :
label_table
Labels with pointers to the list of program statements.
type label_table_t = (string, Absyn.program) Hashtbl.t
unary_fn_table
The unary functions.
type unary_fn_table_t = (string, float -> float) Hashtbl.t
binary_fn_table
The binary functions.
type binary_fn_table_t = (string, float -> float -> float) Hashtbl.t
Because Ocaml is strongly typed, the unary and binary functions need to
be be in separate tables.
variable_table
The simple variables used by the program.
type variable_table_t = (string, float) Hashtbl.t
array_table
The arrays used by the program.
type array_table_t = (string, float array) Hashtbl.t
interp.mli, interp.ml
The interface and implementation of the interpreter. This is the major project
of this program and must be extensively modified.
main.ml
The main function which behaves differently, depending on whether the pro-
gram is run interactively or from the command line. Does the parsing to cre-
ate the abstract syntax structure, then calls the interpreter.
parser.mly
The parser reads a Mini Basic program, verify syntax, and create the abstract
syntax. Specifies the exact syntax of the language.
scanner.mll
The lexical specification for the language, and reads tokens from the source
file.
CSE-112 • Fall 2020 • Program 2 • Interpreter in Ocaml 3 of 3
Makefile
Since the Ocaml project is compiled into a binary executable, as is C++, a
Makefile is needed, as is required in any C, C++, or Java project.
4. What to submit
Submit all of the necessary source files so that the grader may perform the build.
That means submit Makefile, parser.mly, scanner.mll, and all *.mli and *.ml files.
If you are doing pair programming, also submit the files required by the pair-pro-
gramming document. Verify the grading criteria from the .score/ subdirectory.

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