Semantic Overview

  • Function application is call-by-need, except for primitive functions which are strict in every argument. Thus, if the value of a particular argument does not contribute to evaluating the body of a function, then the argument itself never gets evaluated (in the context where it appears). However, no single expression gets evaluated twice in the same (dynamic) scope.

  • Data structures are lazy, meaning that you’re welcome to express an infinite list as long as you don’t consume it all.

  • The logical connectives and and or use short-cut logic: if the expression on the left side determines the result, then the expression on the right side never gets evaluated.

  • case ... when ... then ... else ... esac branching clauses apply tests strictly in order, and evaluate only enough to decide which branch (then or else clause) to take.

  • Explicit lists like [this, that, the, other] are internally translated to nested cons(...) constructions.

  • Strings are considered atomic: they will not participate in a sequence protocol. However, functions may be provided to examine individual characters, take substrings, or iterate through characters.

  • The run-time is free to adjust the order of evaluation or internal representations of things, so long as it preserves the outwardly-observable behavior.

  • Right now, the begin: clause lists expressions. Depending on what sort of expression, Sophie will do different things:

    Simple things like numbers, text, and lists of these:

    Sophie will print these values to the console.

    Messages sent to actors:

    Sophie will work on that message and its consequences until finished, meaning there are neither any messages in flight nor any busy actors or tasks. An active input source (such as the SDL/game event system) is considered “busy” until something makes it shut down.

    Registered Data Types:

    A foreign-function interface module can register a run-time handler for specific types. The turtle-graphics library does this for its drawing type, and the result is a turtle-graphics drawing.

  • Module imports may not form a cycle.