What is a "Domain-specific language" (DSL)?

Examples:

* dates:

* Syntax: "2015-11-18", "third Wednesday in October", "next Saturday"

* Semantic type: |Date|, or perhaps a function type |Date -> Date|

* excel-formulas:

* Syntax: "SUM(A1:A9)", "RIGHT(LEFT(C7,4),2)", ...

* Semantic type: |[ [ Cell ] ] -> Value|

* integrals: [drawing needed]

* (note where variables are bound)

* Heraldry:

https://pyvideo.org/pycon-us-2019/a-medieval-dsl-parsing-heraldic-blazons-with-python.html

Syntax example: "Sable, on a fesse or three lions gules"

Semantics: the resulting drawing?

----------------------------------------------------------------

Surface syntax (mostly ignored in this course)

Abstract syntax (usually a recursive Haskell datatype)

Semantic type (a type of values)

Semantics: a function from AbsSyn -> Sem

eval : AbsSyn -> Sem

Example:

Plus : Syn -> Syn -> Syn -- syntactic constr.

smart constructors:

plus : Sem -> Sem -> Sem -- semantic constr.

-- later on

MySem s => s -> s -> s