Mere - A Minimal Explicit Language

Mere is a minimal, explicit programming language with both Node.js and browser runtimes. It embodies the following design principles:

Design Principles

• Minimal: Minimal keywords, no syntax sugar, no implicit behavior
• Explicit: No hidden behavior, no automatic cleanup, no default values
• Concrete: No user-defined generics, all types are concrete
• Deterministic: Each structure does one thing, each token has a clear role
• Locally Checkable: Errors detected in local scope
• Closure-free: Functions capture no scope; all dependencies are explicit parameters

Language Features

Keywords

fn let mut if elif else while return type import export from true false unit ok err and or not

Types

• Built-in: Number, String, Boolean, Unit, List<T>, Result<T>, Map<K,V>, Task<T>, Fn<A,B,...,R>
• User-defined: Records only (type Point = { x: Number, y: Number })

Variables

• let x = expr — immutable binding
• let mut x = expr — mutable binding
• x = newExpr — reassignment (mutable only)

Control Flow

• if / elif / else — both as statements and as expressions (returns a value)
• while condition { body } — loops
• No exceptions — use Result<T> for error handling

Functions

• Last expression in function body is the return value
• Explicit return for early returns
• Parameters and return types are explicitly annotated
• Named functions with fn, lambda expressions with fn(args) expr
• Tail-call optimization (TCO) for recursive calls

Error Handling

• All fallible operations return Result<T>
• Explicit field access with r.isOk, r.value, r.errMessage
• No try-catch, no ? operator

Concurrency

• join waits for async task completion
• Cooperative scheduling (synchronous appearance)

Browser / Canvas API

Mere supports browser-based 2D drawing via built-in canvas_* functions:

| Category | Function | Params | Description | |----------|----------|--------|-------------| | Clear | canvas_clear | — | Clear entire canvas | | Size | canvas_get_width | — | Canvas width in logical px | | | canvas_get_height | — | Canvas height in logical px | | Color | canvas_set_fill_color | String | Fill color (CSS string) | | | canvas_set_stroke_color | String | Stroke color | | Gradient | canvas_create_linear_gradient | Number x4 | Create linear gradient, returns id | | | canvas_create_radial_gradient | Number x6 | Create radial gradient, returns id | | | canvas_add_color_stop | Number, Number, String | Add color stop to gradient | | | canvas_set_fill_gradient | Number | Use gradient as fill | | | canvas_set_stroke_gradient | Number | Use gradient as stroke | | Font | canvas_set_font | String | Font spec (e.g. "bold 48px sans-serif") | | Text | canvas_fill_text | String, Number, Number | Filled text at (x, y) | | | canvas_stroke_text | String, Number, Number | Outlined text | | | canvas_measure_text | String | Text width in px | | | canvas_set_text_align | String | "left"/"center"/"right" | | | canvas_set_text_baseline | String | "top"/"middle"/"bottom" | | Rect | canvas_fill_rect | Number x4 | Filled rectangle (x, y, w, h) | | | canvas_stroke_rect | Number x4 | Outlined rectangle | | | canvas_clear_rect | Number x4 | Clear rectangle area | | Path | canvas_begin_path | — | Start path | | | canvas_close_path | — | Close path | | | canvas_move_to | Number, Number | Move pen to (x, y) | | | canvas_line_to | Number, Number | Line to (x, y) | | | canvas_arc | Number x5 | Arc (x, y, r, startAngle, endAngle) | | | canvas_arc_to | Number x5 | Arc with control points | | | canvas_stroke | — | Stroke current path | | | canvas_fill | — | Fill current path | | | canvas_set_line_width | Number | Line thickness | | | canvas_set_line_dash | List<Number> | Line dash pattern | | Shadow | canvas_set_shadow_color | String | Shadow color | | | canvas_set_shadow_blur | Number | Shadow blur radius | | | canvas_set_shadow_offset_x | Number | Shadow X offset | | | canvas_set_shadow_offset_y | Number | Shadow Y offset | | Transform | canvas_save | — | Save state stack | | | canvas_restore | — | Restore state | | | canvas_rotate | Number | Rotate (radians) | | | canvas_translate | Number, Number | Translate origin | | | canvas_scale | Number, Number | Scale transform | | Image | canvas_load_image | String | Load image from URL, returns id | | | canvas_draw_image | Number x5 | Draw image (id, x, y, w, h) | | | canvas_image_loaded | Number | Check if image is loaded | | Audio | audio_load | String | Load audio from URL, returns id | | | audio_play | Number | Play audio | | | audio_pause | Number | Pause audio | | | audio_resume | Number | Resume audio | | | audio_stop | Number | Stop and reset audio | | | audio_set_volume | Number, Number | Set volume (id, 0-1) | | | audio_set_loop | Number, Boolean | Set loop mode | | Events | canvas_on_click | Fn | Register click handler (x, y) | | | canvas_on_drag | Fn | Register hover/mousemove handler (x, y) | | | canvas_on_dblclick | Fn | Register double-click handler (x, y) | | | canvas_wait_click | — | Wait for click, returns Task<Map> | | | canvas_wait_drag | — | Wait for drag, returns Task<Map> | | Cursor | canvas_set_cursor | String | Set CSS cursor style | | Math | sin | Number | Sine | | | floor | Number | Floor | | | round | Number | Round | | | pi | — | Pi constant | | | now | — | Current timestamp (ms) | | | random | Number | Random int in [0, n) | | Await | await_font_loaded | — | Wait for font loading | | | next_frame | — | Wait until next animation frame |

Use mere build to produce a standalone HTML file that inlines the runtime and your .mere code.

Module System

• Flat modules (no nesting)
• Explicit export and import
• File name = module name

Installation

cd mere
npm install
npm run build            # Compile TypeScript + build browser bundle

Usage

# Run a Mere program (Node.js)
mere examples/hello.mere

# Run tests
npm test

# Build for browser — produces standalone HTML
mere build examples/browser/rectangles.mere
open rectangles.html   # Works directly in browser

# Options
mere build input.mere -o output.html --width 1024 --height 768

Examples

| File | Description | |------|-------------| | examples/hello.mere | Hello World | | examples/factorial.mere | Recursive factorial | | examples/fibonacci.mere | Recursive Fibonacci | | examples/error_handling.mere | Result-based error handling | | examples/data_structures.mere | Lists and Maps | | examples/records.mere | Custom record types | | examples/browser/rectangles.mere | Canvas drawing (browser target) | | examples/browser/game.html | Browser game (Touhou-themed card game) | | examples/browser/events.mere | Click/drag event handling |

Language Specification

See docs/usage.md for the complete language reference.

Limitations (Intentional)

• No user-defined generics
• No pattern matching
• No exceptions
• No automatic resource management
• No inheritance/interfaces/polymorphism
• No operator overloading
• No reflection/metaprogramming
• No channels (use file I/O)

License

MIT