Coral language specification

Coral is a simple language for learning programming. Coral has a code (text) version and a flowcharts version, representing the same underlying language. This spec is for the code version. Coral’s spec is brief, because the language is simple, but includes the constructs taught in most introductory programming classes (variables, assignments, branches, loops, arrays, functions). Language design decisions are discussed on our philosophy page. See http://corallanguage.org for more.

Declaration and statement constructs

Construct Form
Variable declaration 
[type] [identifier]
Input statement 
[var] = Get next input
Output statement 
Put [item] to output
Assignment statement 
[var] = [arithexpr]
Branch statements 
if [condexpr]
   [substatements]
elseif [condexpr]
   [substatements]
else
   [substatements]
While loop statement 
while [condexpr]
   [substatements]
For loop statement 
for [init]; [condexpr]; [update]
   [substatements]

Declaration/statement examples and notes

Construct Examples and notes
Variable declaration 
integer numCoins
float numInches
  • Valid types: integer, float
  • Identifier: Letter followed by any letters, numbers, or underscores
  • Can only be at top of function
Input 
x = Get next input
  • x must be a variable
Output 
Put "Hi all" to output
Put x to output
  • Output item is usually a string literal or variable (but may be an arithmetic expression)
Assignment 
x = (y + z) / 2
  • Left must be a variable, right an arithmetic expression. Arithmetic operators: +, -, *, /, %
  • Precedence: (), unary -, * / %, + -, left-to-right
Branch 
if (y - z) < 10
   Put "Close" to output
if x < 10
   Put "Small" to output
elseif x < 20
   Put "Med" to output
else
   Put "Large" to output
  • elseif is optional, any number OK
  • else is optional, must be last
  • Conditional expression’s operators: (), ==, !=, , =, and, or, not
  • Precedence (high to low): (), not, * / % + -, < >=, == !=, and, or
While loop 
while userInput > 0
   Put userInput to output
   userInput = Get next input
For loop 
for i = 0; i < 4; i = i + 1
   Put i to output

Other constructs

Construct Form
Comments 
// [any text]
Arrays 
[type] array([size]) [identifier]
Functions 
Function [identifier]([parameters]) returns [type] [identifier]
   [substatements]
Built-in math functions 
SquareRoot
RaiseToPower
AbsoluteValue
Built-in random functions 
RandomNumber
SeedRandomNumbers
More output features 
Put floatvar to output with 3 decimal places

Other constructs examples and notes

Construct Examples and notes
Comments 
// Read data
x = Get next input
  • Must appear on own line
Arrays 
integer array(5) userNums
float array(5) userVals
x = userNums[3]
y = userNums.size
  • Type is integer or float, size must be > 0
  • Access uses [ ] notation. Indices are 0 to size-1
  • userVals.size attribute available.
  • size of ? OK, must set size before access. Ex:
integer array(?) userNums
userNums.size = 5
Functions 
Function FtInchToCm(float numFt, float numInch) returns float numCm
   numCm = ((numFt * 12) + numInch) * 2.54
  • 0 or more parameters. 2 or more separated by comma
  • 0 or 1 return variable. If 0, use: returns nothing
  • Last value in return variable is returned
Built-in math functions SquareRoot(9.0) evaluates to 3.0
RaiseToPower(2.0, 4.0) evaluates to 16.0
x = AbsoluteValue(-15.2) evaluates to 15.2
Built-in random functions 
SeedRandomNumbers(5)
x = RandomNumber()
  • Setting seed first is optional (default seed is 0)
  • Seed typically only set once, at start of program (if at all)
Output 
float f
f = 99.13579
Put f to output with 3 decimal places

yields: 99.136

More language details

  • All sub-statements are indented 3 spaces.
  • Do not need to specify functions, in which case the program is implicitly in a Main function definition having no parameters and returning nothing. However, if any function is specified, then all code must be in functions, with Main explicitly defined. No global code allowed.
  • Arithmetic type conversions
    • For an arithmetic operator, if either operand is a float, the other is automatically converted to float, and then a floating-point operation is performed.
    • For assignments, the right side type is converted to the left side type.
    • integer-to-float conversion is straightforward: 25 becomes 25.0.
    • float-to-integer conversion just drops the fraction: 4.9 becomes 4.
  • Conditional type conversions are not allowed. Ex: not 1 is not allowed.