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Compiling and Loading the micro-SML Compiler

Chapter 13 presents the micro-SML language, a subset of Core Standard ML and an extension of micro-ML. This rounds off the topic of functional languages by putting together many of the previously discussed topics of higher-order functions, polymorphic type inference, heap allocation, garbage collection, continuations and local optimization techniques previously applied to micro-C.

Building the micro-SML command line compiler

The compiler has been tested on .NET 8, .NET 9 and .NET 10**.

Choose the desired .NET version in the microsmlc.fsprog file by changing:

<TargetFramework>net10.0</TargetFramework>

to one of

  • net8.0
  • net9.0
  • net10.0

Make MicroSML current directory.

To build the compiler, run:

dotnet build microsmlc.fsproj

or simply:

dotnet build

For example:

dotnet build
Restore complete (0,1s)
microsmlc net10.0 succeeded (0,1s) → bin/Debug/net10.0/microsmlc.dll

Build succeeded in 0,4s

The build process automatically runs the lexer and parser generators whenever either FunLex.fsl or FunPar.fsy has changed.

The compiled compiler executable is placed in:

bin/Debug/net10.0/microsmlc.dll

Compiling a micro-SML program

To compile a micro-SML program, for example SmlEx/ex01.sml, run:

dotnet run SmlEx/ex01.sml

This compiles ex01.sml from the SmlEx directory and generates the output file:

SmlEx/ex01.out

Example:

dotnet run SmlEx/ex01.sml
Micro-SML compiler v 2.0 of 2026-05-30
Compiling SmlEx/ex01.sml to SmlEx/ex01.out.

Compiler options

The compiler supports below options:

Option Description
-debug outputs intermediate AST and other debug information on terminal
-verbose outputs intermediate program transformations on terminal
-eval Interpretates the program and outputs result on terminal.
-alpha Performs alpha conversion, left as exercise.
-opt Performs local peephole optimizations.

Example:

dotnet run -eval -verbose SmlEx/ex01.sml

Options can be combined arbitrarily.

The Micro virtual machine

The micro virtual machine, micro-VM, is located in the MicroVM directory, where the file README.md explains how to build and use it.

The result is an executable named:

  • microvm (Unix/macOS)
  • microvm.exe (Windows)

located in the MicroVM directory.

A complete example

The following example demonstrates compiling and executing queens.sml.

  1. Change to the MicroSMLdirectory.

  2. Compile the program

dotnet run SmlEx/queens.sml
Micro-SML compiler v 2.0 of 2026-05-30
Compiling SmlEx/queens.sml to SmlEx/queens.out.
  1. Run the compiled program using micro-VM:
../MicroVM/microvm SmlEx/queens.out
[[[6,5] ,[5,3] ,[4,1] ,[3,6] ,[2,4] ,[1,2] ] ,
  [[5,4] ,[4,2] ,[3,5] ,[2,3] ,[1,1] ] ,
  [[4,3] ,[3,1] ,[2,4] ,[1,2] ] ,[] ,[] ,[[1,1] ] ]

Result value: #33629982712
Used 1 cpu milli-seconds
Number of GC: 0

Micro-SML example programs

The micro-SML compiler comes with a test suite of 50 test programs covering both static and dynamic semantics.

The test programs are in the SmlEx directory.

  • Programs named exXX.sml compiles and run with micro-SML. The program queens.sml used above is an example.

  • Programs named exFXX.sml demonstrate expected compile time errors, such as type errors.

For example, exF02.sml demonstrates a problem unifying two types that cannot be unified.

Example:

dotnet run SmlEx/exF02.sml
Micro-SML compiler v 2.0 of 2026-05-30
Compiling SmlEx/exF02.sml to SmlEx/exF02.out.

Type error: bool and int

Micro-SML test suite

Micro-SML includes an automated test suite located in:

SmlEx/test.fsx

The test suite consists of three categories of test programs:

  1. Programs that compile and run with Micro-SML, exXX.sml.

These verify static and dynamic semantic compliance.

  1. Same as 1), but focus on generative exceptions, exnXX.sml.

  2. Programs that fail to compile with micro-SML due to type errors.

These verify the static semantics.

Run the test suite from the SmlEx directory:

dotnet fsi test.fsx
Setting current directory to MicroSML
Delete all *.out files in SmlEx directory.
Compiling file with options -eval: ex01.sml
outMatch: [5]

Compiling file with options : ex01.sml

micro-SML out: [5]
 5

...

Result of test.
ex01.sml(Eval): OK
ex01.sml(Comp): OK
ex01.sml(Comp+Opt): OK
ex02.sml(Eval): OK
ex02.sml(Comp): OK
ex02.sml(Comp+Opt): OK
ex03.sml(Eval): OK
...

The test script

  • compiles and runs all test programs.
  • compiles with different combinations of compiler options. See test.fsx for the combinations used.
  • compares each execution with the expected output.
  • summarizes the results at the end.
  • works across multiple platforms.

Note The test suite runs relatively slow because it launches external system processes to compile and execute the programs.